Advanced Ocular

Assessment

Prepared by

Prof. Dr. Mohamed Khafagy

A.Professor of Ophthalmology Faculty of Medicine,

Cairo University

Second Year

2018-2019

Acknowledgments

This two-year curriculum was developed through a participatory and collaborative approach between the

Academic faculty staff affiliated to Egyptian Universities as Alexandria University, Ain Shams University, Cairo

University , Mansoura University, Al-Azhar University, Tanta University, Beni Souef University , Port Said

University, Suez Canal University and MTI University and the Ministry of Health and Population(General

Directorate of Technical Health Education (THE). The design of this course draws on rich discussions through

workshops. The outcome of the workshop was course specification with Indented learning outcomes and the

course contents, which served as a guide to the initial design.

We would like to thank Prof.Sabah Al- Sharkawi the General Coordinator of General Directorate of Technical

Health Education, Dr. Azza Dosoky the Head of Central Administration of HR Development, Dr. Seada

Farghly the General Director of THE and all share persons working at General Administration of the THE for

their time and critical feedback during the development of this course.

Special thanks to the Minister of Health and Population Dr. Hala Zayed and Former Minister of Health

Prof. Ahmed Emad Edin Rady for their decision to recognize and professionalize health education by issuing a

decree to develop and strengthen the technical health education curriculum for pre-service training within the

technical health institutes.

ذىصف هقشس دساس

تااخ الوقشس -1

القاساخ الورطىسج لوشض العىى اسن الوقشس : الشهض الكىدي :

Advanced Ocular Assessment

الثاح الفشقح /الوسرىي :

الرخصص : الثصشاخ

عول 6ظشي 3عذد الىحذاخ الذساسح :

To provide training for the Ophthalmic Technician in advanced هذف الوقشس: -2

ophthalmic assessment procedures to perform them in a clinical

setting under the appropriate supervision of an Ophthalmology

specialist.

الوسرهذف هي ذذسس الوقشس : -3

ا. الوعلىهاخ

:والوفاهن

By the end of this course the trainee will be able to:

Describe the equipment used in advanced assessment of eye

patients and explain its value in patient service.

Identify different sources of errors affecting the results of

ophthalmic equipment and how to minimize them.

Know the different types of low vision aids equipment and

their proper use with the patients.

الزهح : الوهاساخ -ب

By the end of this course the trainee will be able to:

Apply the advanced ocular assessment techniques accurately

and guide the patient properly during examination.

Compare the different methods used to examine the eye and

interpret their results accordingly.

Confirm the results of different ocular assessment techniques

and report them correctly.

الوهاساخ الوهح -ج

الخاصح تالوقشس:

By the end of this course the trainee will be able to:

Assess visual acuity of a low vision patient and recommend

Low vison aid use accordingly.

Perform and record in-office ocular assessments such as:

Tonometry, color vision, pachymetry, Amsler Grid, automated

or manual lensemeter and automated or manual Keratometer.

Carry out ocular ultrasound and Biometry and IOL

calculations and document it accurately.

Investigate and analyze the eye suing corneal topography,

automated perimetry, fundus photography and optical

coherence tomography (OCT).

الوهاساخ -د

العاهح :

By the end of this course the trainee will be able to:

Operate computers and medical software.

Respond to patients‟ inquiries and frequent questions.

Provide proper advice concerning advanced ocular testing.

هحرىي الوقشس: -4

1. Low Vision

Definition of low vision

Measuring visual acuity of a low vision patient

Calculation of required magnification

Types of low vision devices (optical and non-optical)

Advantages and disadvantages of different low vision

devices

2. Supplementary Tests

Color Vision

Stereoacuity and glare

Tonometry

Pachymetry

Lensometry

Keratometry

Manual perimetry, Tangent screens and confrontation field

tests.

Automated perimetry

Internal eye examination:

direct ophthalmoscopy

indirect ophthalmoscopy

slit lamp lenses

3. Ophthalmic Imaging:

external eye and slit lamp photography

A-scan Ocular Ultrasound and IOL calculation

B-scan Ocular Ultrasound

corneal topography

fundus photography

Scanning computer ophthalmic diagnostic imaging

(optical coherence tomography [OCT], GDx, HRT)

ة الرعلن والرعلنأساا -5

Academic Lectures.

Assignments.

Practical hands–on training.

أسالة الرعلن والرعلن -6

للطالب روي القذساخ

.الوحذودج

Extra tutoring hours.

Small number training sessions.

Supportive feed-back.

Involve in projects and helpful assignments.

Forming peer support groups.

اخرثاساخ ظشح ذقىن الطالب -7

اخرثاساخ عولح

األسالة الوسرخذهح -أ

(Essay & MCQاخرثاساخ ظشح )

(Slide show) اخرثاس عول عل صىس وسائط هرعذدج

عل االجهضج ارظام حضىس الرذسثاخ العولح

Mid-term assessment (MCQ) by 7 الرىقد -بth

week

Final assessment (Essay, MCQ & Slide show) by 15th

week

ذىصع الذسجاخ -ج

دسجح 90دسجح والصغشي 150الهاح العظو

دسجح 20اعوال سح

دسجح 40العول

دسجح 90اخرثاس ذحشش

الذساسح والوشاجع :قائوح الكرة -8

Ophthalmic Medical Assisting, An Independent Study Course, (E. Newmark &

M.A. O’Hara, 6th Edition, 2012, AAO).

The Ophthalmic Assistant, 9th Edition, (H.A. Stein, R.M. Stein and M.I.

Freeman, Eighth Edition, 2013, Elsevier Inc.)

Fundamentals for Ophthalmic Technical Personnel, (B. Cassin, 1995, W.B.

Sanders Company.

----- هزكشاخ -أ

----- كرة هلضهح -ب

. Certified Ophthalmic Assistant Exam Review Manual, (J كرة هقرشحح -ج

K. Ledford, Slack.)

دوساخ علوح أو -د

ششاخ ...... الخ

International Council of Ophthalmology website:

www.icoph.org/resources.html

American Academy of Ophthalmology website:

Eyewiki.aao.org

American Academy of Optometry website and journal:

www.aaopt.org

Course Description .............................................................................................. vi

Chapter 1: Low Vision..........................................................................................9

Chapter 2: Supplementary Vision Testing.........................................................22

Chapter 3: Ophthalmic Imaging ......................................................................... 47

Bibliography and Recommended Readings......................................................60

Appendices ....................................................................................................... 61

لىصاسج الصحح والسكاى وحزس تعهحقىق الشش والرألف

Contents

This course aims to provide training for the Ophthalmic Technician in advanced ophthalmic

assessment procedures to perform them in a clinical setting under the appropriate supervision of an

Ophthalmology specialist.

Core Knowledge

By the end of this course, students should be able to:

Describe the equipment used in advanced assessment of eye patients and explain its value in

patient service.

Identify different sources of errors affecting the results of ophthalmic equipment and how to

minimize them.

Know the different types of low vision aids equipment and their proper use with the patients.

Investigate and analyze the eye suing corneal topography, automated perimetry, fundus

photography and optical coherence tomography (OCT).

Core Skills

By the end of this course, students should be able to:

Apply the advanced ocular assessment techniques accurately and guide the patient properly

during examination.

Compare the different methods used to examine the eye and interpret their results accordingly.

Confirm the results of different ocular assessment techniques and report them correctly.

Assess visual acuity of a low vision patient and recommend Low vison aid use accordingly.

Perform and record in-office ocular assessments such as: Tonometry, color vision,

pachymetry, Amsler Grid, automated or manual lensemeter and automated or manual

Keratometer.

Course Description

Course Overview

Methods of Teaching/Training with

Number of Total Hours per Topic

ID

Topics

Inte

ract

ive

Lec

ture

Fie

ld W

ork

Cla

ss

Ass

ign

men

ts

Res

earch

Lab

1 Low Vision

21 2 4 8

2 Supplementary Vision Testing

21 10 8 8

3 Ophthalmic Imaging

21 12 12 8

TOTAL HOURS (108) 63 24

24 24

Objectives

Defining low vision

Measuring visual acuity of a low vision patient

Calculation of required magnification

Types and advantages of different low vision devices (optical and non-optical)

Introduction and Definition of Low Vision

Low Vision

Because of disease, developmental abnormalities or trauma, certain patients do not obtain satisfactory

vision even when their ametropia is fully corrected. A low vision patient is a patient with subnormal

visual acuity or abnormal visual field, that can‟t be corrected by spectacles or contact lenses (usually less

than 6/24).

Vision rehabilitation is a necessary part of complete eye care. Many patients have been told that their

vision cannot be improved, which has caused them to believe that they will be forced to leave their work

or their special interests, or both. Seeing a visually impaired person reading after losing hope that

something can be done is a more striking event than seeing a postoperative cataract patient read the 6/6

line. To an adult, this may mean the opportunity for resuming or gaining work. Children can be given the

opportunity to have proper education and allow them to participate with other children in the classroom.

For the elderly person can prevent depression because of inability to read, write, or keep up hobbies. The

rehabilitation of a low vision patient could be very satisfying, for both the patient and the provider.

Low Vision Aids are prescribed to patients who cannot carry out their routine activities even with

glasses. These are special types of spectacles, which are prescribed to patients with very poor vision.

Low Vision

Low vision aids are usually indicated in the following conditions:

A. Retinal and optic nerve diseases such as:

1. Macular lesions and dystrophies.

2. Advanced glaucoma.

3. Diabetic retinopathy.

4. Optic atrophy.

5. Pathological myopia.

6. Toxic and strabismic amblyopia.

B. Corneal diseases as in:

1. Corneal opacities.

2. Irregular astigmatism.

Measuring Visual acuity of a Low Vision Patient

Visual Acuity testing:

It is important in the eye examination to test visual acuity accurately. Low vision patients are

better tested using specific low vision eye charts for both distance and near acuity (Figure 1)

that are different from the eye charts used in a regular eye examination as most charts and

projectors have no test print between 6/30 and 6/60 or beyond 6/60. Hence, the partially

sighted patient should be tested at 3 m instead of at 6 m with Snellen charts or specially

designed test charts (ETDRS). Afterwards the result is multiplied by 2 to convert it to standard

notations; for example, 3/24 = 6/48. If the acuity is less than 3/60 (i.e. 6/120), the chart is

brought closer to the patient until the 60 letter is identified (2/60, 1/60). „Counting fingers‟ is

not preferable to be used as a visual acuity test. (See appendix 1 for details on how to measure

visual acuity in a low vision patient).

Refraction:

A careful refraction is important because correction of a basic refractive error will improve the

patient‟s vision and will also work as baseline acuity for the prescription of other optical

magnifying devices. A good refraction and an increase in a bifocal add is often the best

solution for a patient with early vision loss. A patient with high myopia may be able to read

without glasses, but need a new prescription for distance. Once a good refraction is obtained,

the reading add is determined.

In a patient with a visual impairment, every small improvement in vision offers the

opportunity for improved function. Refracting a low-vision patient may require more patience

than with other patients, but the principles are the same. It is important for the patient to see

the chart and more than one letter or number. When checking between two lenses, give the

patient more time to see and answer than a patient with normal vision; patients with

nystagmus need extra time to focus before determining their choice.

Bailey-Lovie Acuity Chart Early Treatment of Diabetic Retinopathy Study (ETDRS) Chart

MN Read Low Vision Acuity Chart Lighthouse Near Visual Acuity Chart

Figure 1: Examples of specialized Low vision charts.

Advantages of Spectacles:

Spectacles allow the patient to function hands free.

They provide a large reading field, but with a close and fixed working distance.

Spectacles allow the inclusion of shades to reduce glare and improve contrast.

They allow adding prisms to assist the patient in finding an area of the retina

that offers improved vision.

They can offer the incorporation of high adds for magnification. These lenses

need base-in prism to reduce the demand on convergence.

Field of vision testing (chapter 2 ): (Central & peripheral)

The Amsler Grid Test (Central field): The Amsler Grid test looks like a

piece of white graph paper with darker horizontal and vertical lines that form a

square grid (Figure 2-left). Wavy, distorted, missing or broken lines, or holes

or black spots in the grid can indicate macular problems (figure 2- right).

The Amsler Grid The Amsler Grid of a patient with macular degeneration

Figure 2: Amsler Grid.

Automated Visual Field Testing: (Central & peripheral) To determine accurately

the visual field of the patient, using a computerized visual field analyzer, such as the

Humphrey Visual Field Analyzer (Figure 3- left), or a non-computerized visual field

test, such as the tangent screen or the Goldmann Perimeter (Figure 3- right).

Humphrey Field Analyzer Goldmann Perimeter

Figure 3: different types of perimeters.

Other advanced vision assessment Tests: (see chapter 2)

Depth perception

Color vision

Glare sensitivity and Response to different lighting conditions and ocular filters.

Calculation of required magnification

Kestenbaum's rule

A. In Kestenbaum's rule, first we calculate the power of the lens required by the patient by

dividing the denominator of the Snellen acuity by the numerator. For example, a person

with 6/60 vision needs a +10 (60/6) diopter lens to read J5 (6/18) print. If we need the

patient to read J1 (6/6) print this number is doubled i.e. the same patient will need +20 D

for J1 print.

B. Magnification achieved is calculated by multiplying the reading distance in meters by the

power of the lens.

If we chose a focal length of 25 cm (0.25 meters) the magnification achieved with

a + 10 diopter lens would be 2.5x (10 x 0.25= 2.5), i.e. divide the power of the

lens by 4 for a focal length of 25 cm. Thus , the degree of magnification achieved

by a + 10 D lens would be 10/4 or 2.5x, a +8 D lens gives 2x magnification and a

+20 D lens 5x magnification.

C. This could be used as a rule of thumb, with further refinement for a specific task

requirement by a patient. Children and young adults would need less than a +5.00 lens

because of accommodation, and usually the weakest lens that would enable reading of J5

on the near-vision chart is added to his spectacle distance correction. In addition, word

and text charts are helpful in assessing magnification requirements of these patients.

D. For viewing distant objects, telescopes or binoculars can be useful. Although

Kestenbaum‟s rule is helpful, the patient usually will have to try two or three aids before

matching an aid to the desired activity or task.

Types and advantages of different low vision devices (optical and non-optical)

Many vision rehabilitation devices are now available to assist patients with glare, photophobia,

mobility, and normal daily functioning. Any device that improves a patient‟s vision, even a small

improvement, should be considered for patient use as it may help him return to normal daily activities.

These devices could be optical or non-optical.

Optical Low vision Aids:

A. Magnifying glasses:

Principle: The convex lens acts as a magnifying loupe.

The object is placed inside F1 of the lens with a magnified virtual image is viewed

by the eye (figure 4).

Figure 4: Magnification by a convex lens.

Types of magnifying glasses: (Figure 5)

Hand-held magnifiers:

o Magnifying lenses: A biconvex or planoconvex reading lenses of different sizes and

powers (from +4 D to +20 D usually).

Advantages:

Easy to carry and use.

Increased reading range: The distance between the eye and the lens can be varied

quickly depending on the reading distance and the magnification needed.

Disadvantages:

Small visual field: as the lens power increase, the field of view decreases).

Distortion of image by optical aberration.

o Press-on membrane Fresnel lens (stepped lens): Thin plastic flexible membrane.

Advantages: Very thin lens with no decreased diameter at higher magnifications.

Disadvantage: mild image distortion from increased diffraction of the little prisms on

the Fresnel lens.

Stand magnifiers :

o Stand magnifiers rest the magnifier directly on the material to be seen.

o The power of these magnifiers can be up to 60 D and some are illuminated.

o The stand magnifier helps the patient in writing by placing the pen or pencil under the

magnifier between the legs of the stand (Figure 5- upper right).

o It is best for older patients with tremors, and for younger children trying to keep their

position while reading.

Neck-held magnifiers: Are resting on the chest leaving the hands free (Figure 5- lower

left).

Spectacle-born high-plus reading lenses: (+4 D to +20 D.)

o Forms:

Single vision forms: Monocular or binocular.

Bifocal forms: Bifocals with high powers up to +32 D (8x). Lens decentration or add a

prism base-in is usually needed especially in case of powers higher than 5 D.

Dome convex lens: Dome-shaped convex lens which has high converging power that

is laid on print and produces magnification of the letters (Figure 5- upper left).

Convex cylindrical lenses: a Bar-shaped lens which has no refractive power or only a

low converging power in its long axis and high converging power in cross section is

laid on a line of print and produces vertical magnification of the letters (Figure 5-

lower right).

Figure 5: different types of optical low visual aids.

B. Telescopic lenses: Galilean or Astronomical telescopic system (Figure 5-upper left).

o Principle: Telescopes allow magnification of an object in the distance by

increasing the retinal image size.

o Forms:

Hand-held or spectacle-mounted.

Binocular or monocular.

Some are fixed but most can be focused.

o Advantages:

Allow the magnification at a greater distance than ordinary magnifying

lenses so could provide vital support for distance viewing, giving the

patient greater flexibility.

A simple telescopic spectacle without a casing is available and is

lightweight and relatively inexpensive.

Telescopes allow the spotting of street signs, classroom materials, bus

signs, shows and movies and speakers in a classroom or lecture.

o Disadvantages:

Small field of view (patients cannot wear a telescopic device when

walking).

Poor contrast or illumination

Limited depth of focus.

C. Projection devices: They are useful for reading and writing (Figure 6)

Principles:

Projection magnifiers: form an enlarged image on a translucent screen at

a variable distance.

Closed-circuit television magnification system (CC-TV): Project a

magnified image onto a screen.

Advantages:

They are easily adopted by the patient.

High relative distance magnification in addition to the relative size

magnification by projection (up to 60x).

Image with greater brightness and more contrast than the original object.

Greater magnification range up to 40 times with reduced aberrations.

A more normal viewing or reading distance.

Reversed polarity (with white print on black with improved contrast).

Figure 6: Projection low vision aid (CCTV).

D. Non-magnifying low vision aids:

Pinhole spectacles:

Indications:

o To improve reading vision in opacities of ocular media.

o To determine the potential vision if retinoscopy is not possible.

Reading slit (typoscope):

Black device with a rectangular opening to read one or more lines at a time

in: Early cataracts due to increased contrast.

Training of centric viewing in macular diseases.

Colored Filters (figure 5 – upper left):

Could be used for patients with glare and Photo-sensitivity problems such

as in Albinism and Cone dystrophy.

Non-optical low vision aids:

These are aids other than lenses especially writing aids as black ink marking pens,

large type books, signature guides and telephone dials (Figure 7).

Figure 7: Non-Optical low visual aids.

Lighting:

Good lighting is an important visual aid for everyone. Lighting increases contrast

between print and the background, thereby making details more clear.

The best contrast is achieved by good type with black print on a white or near-

white background.

The failure of an optical or non-optical visual aid to work in the patient‟s home

when success was shown in office testing often means that the home setting has

inadequate lighting.

Selection of low-vision aids:

No single visual aid is best, because each patient must be considered in terms of

functional loss, age, interests, motivation, and the type of activity for which the aid is

intended.

For example; an old person with a tremor may benefit from a stand magnifier or

spectacles. High-tech devices might be essential for someone at work to keep his job.

Patients who have recently lost vision may need time to accept this. A multidisciplinary

approach to the care of these patients is very helpful.

Low-vision rehabilitation includes besides low visual aids orientation and mobility

(O&M) training (learning how to work in the kitchen safely, and how to navigate the

home) and Psychological and social support through psychologists and social workers to

educate the patient, his family and social circles to deal with the new environment of this

disability.

22

Objectives

Describe different ancillary ocular testing technique

Know the basics of Operation of different clinical equipment in eye clinic.

Overview

Advanced ocular assessment techniques studied in this chapter include:

Color Vision

Stereoacuity and glare

Tonometry

Pachymetry

Lensometry

Keratometry

Perimetry.

Ophthalmoscopy:

• direct ophthalmoscopy

• indirect ophthalmoscopy

• Slit lamp lenses

Color Vision

Color depends on:

o Hue: object will have a particular hue because it reflects or transmits light of a certain

wavelength.

o Saturation: it is an index of the purity of a hue i.e. the shade or the amount of black

color given to a hue.

o Brightness: this depends on the light intensity.

Color is perceived by the cones Located mainly in the central retina i.e macula.

Normal cones have three photosensitive pigments: red, green, blue.

Supplementary Ocular Testing

23

Color vision defects arise from a deficiency or absence of one or more visual pigments. Defects

in color vision may be congenital or acquired.

o Congenital color defects occur in about 8–10% of males and in only 0.4% of females.

This defect is transmitted through the female and appears predominantly in the male (X-

linked pattern of inheritance).

o Acquired color blindness may occur after diseases of the optic nerve or central retina.

Clinically, persons with abnormal color vision fall into three major categories:

o The trichromat has all three cone pigments intact and has normal color vision. The

anomalous trichromat has a partial deficiency of one of the three cone pigments:

Protanomaly: deficient mainly in red visual pigment and poor red-green

discrimination.

Deuteranomaly: deficient mainly in green visual pigment and poor purple-green

discrimination.

Tritanomaly: deficient mainly in blue visual pigment and poor blue-yellow

discrimination.

o The dichromat has a complete deficiency in one cone pigment but the other two visual

pigments are intact. Also three types

Protanopia: in which red is absent.

Deuteranopia: in which green is absent.

Tritanopia: in which blue is absent.

o The monochromat has only one type of cone pigment (e.g blue monochromatism has

only the blue visual pigment) (very rare).

In the majority of patients, the color deficiency is in the red–green area of the spectrum. With

the deficiency in red, this color appears less bright than for the normal individual and thus

mixtures of colors containing red are often confused with other colors.

24

Color vision testing is important to assess the following:

o Evaluate color blindness and degrees of color blindness

o Macular diseases.

o Chloroquine Toxicity

o Cone Dystrophy

o Optic nerve diseases e.g. in Multiple Sclerosis.

Color Vision is tested by a group of specialized test:

o Color plates (easy to use but crude): (Appendix 2)

Ishahara color plates test (Figure 8- above): These are a series of

pseudoisochromatic plates that determine total color blindness and red-green

blindness. They consist of dotted numbers of one color against a background of

another color.

Hardy-Rand-Ritter plates (Figure 8- below): Same concept as Ishahra plates but

more accurate in determining red-green and yellow-blue anomalies.

o Color matching tests (difficult to apply but more accurate):

Fransworth-Munsell 100-Hue test (FM-100) (Figure 9-above): Has 85 rainbow

colored caps in four trays. Patients are asked to arrange the caps and then the

trays are scored. It is time consuming and difficult to score.

FM D-15 test (figure 8-right): same as FM-100 but with 15 pastel chips to be

arranged in a color sequence and scored. It is easier to score and less time

consuming than FM-100.

25

Ishihara pseudoisochromatic plates

Hardy-Rand-Ritter plates

Figure 8: Color vision testing plates.

26

Fransworth-Munsell 100-Hue test

Fransworth –Munsell D-15 test

Figure 9: matching Color vision tests.

Stereoacuity and Glare testing

Stereoacuity testing:

o It measures depth perception.

o Depth perception requires: good vision in both eyes, normal alignment of both eyes and

overlapping visual fields.

o Titmus Fly Stereotest (figure 10):

Consists of various vectograms seen through polarized glasses.

It includes one with a stereoscopic pattern representing a housefly (figure 10).

The patient wears the polarized lenses and asked to touch the wings of a fly. If

the patient has depth perception, the wings will appear to stand out before the

27

picture.This patient will have gross stereopsis of approximately 200 seconds of

arc.

Wirt stereo tests: (Figure 10)

This is suitable to young school-aged children and older. Animals in three

lines are shown. If all three lines of animals are correctly selected, the

patient has stereopsis of approximately 100 seconds of arc.

The raised rings in nine frames are shown to older children, adults, or

even younger children, if possible, depending on the alertness of the

child. If all nine groups are correctly selected, it may be assumed that the

patient has normal stereopsis of approximately 40 seconds of arc. In this

portion of the test, two groups must be missed in succession for the

examiner to stop the test. For example, if the patient correctly selects

groups 1 through 6 and misses groups 4, 7, and 8, number 6 would be

counted as the patient‟s maximum amount of stereopsis.

Figure 10: Titmus Fly test.

28

o Worth 4-dot test:

A clinical test for suppression that tests fusion and binocularity.

The test involves an illuminated target and a pair of modified eyeglasses (figure

below). The flashlight target has 4 lighted dots: 1 white, 1 red and 2 green.

The eyeglasses have a red filter on the right side and a green filter on the other

side.

The patient wears the spectacles and views the 4-dot target. In this configuration,

the right eye will see 2 red dots, the left eye will see 3 green dots.

Patients capable of fusion will fuse the 2 images and report a total of 4 dots, with

the fourth white dot perceived as either green or red. Sometimes it is perceived

as alternating between red and green. Either way, the patient sees only 4 dots

because he or she is "fusing" the white dot with both eyes.

Patients with suppression will report either 2 dots (left eye suppression) or 3 dots

(right eye suppression). Suppression causes the brain to ignore images from one

eye. Therefore, patients with suppression will only see the dots with the non-

suppressed eye.

Five dots is the diplopic or double vision response unless the patient has

alternating suppression. To distinguish between diplopia and alternating

suppression, ask the patient if all 5 dots are seen simultaneously. A person with

rapidly alternating suppression will see 3 then 2 then 3 then 2 dots.

29

Figure 11: Worth 4-dot Test. (RE= Right eye. LE = Left eye)

Glare Testing:

o Corneal and Lenticular opacities may induce glare (Figure 12).

o The effects of glare on vision can be measured by Halogen Glare test (figure 13-left) or

by BAT (Brightness Acuity Test) (figure 13-right):

The patient looks at Snellen charts arranged on a halogen light chart either

directly or through a specific BAT machine.

The patient reads the letters and his visual acuity (VA) is recorded.

The examiner then turns on the lights that shine directly into the patient‟s eyes.

With the lights on, the patient is instructed to read the letters on the chart.

The acuity is measured after glare testing is recorded.

With high-beam light, this usually falls off considerably if there are glare-causing

opacities present.

30

o Other: Miller-Nadler glare tester, transilluminator.

Vision with glare and halos Normal vision

Figure 12: Effect of glare on vision.

Halogen Glare test Brightness Acuity test (BAT)

Figure 13: Glare Testing.

31

Tonometry

Measuring intraocular pressure (IOP), or tonometry, is an essential part of all eye examinations for

adults and children to detect undiagnosed glaucoma. Intraocular pressure (IOP) is determined largely by

the outflow of aqueous humor from the eye: the greater the resistance to outflow, the higher the IOP.

IOP varies among individuals within a range from 10 to 21 mm Hg and the mean IOP is 15 mm Hg. The

tools used to measure the IOP are called tonometers.

Types of Tonometers (Figure 14): (Appendix 3)

o Applanation Tonometer (The Gold standard):

A specific known area of the cornea is flattened and the amount of force needed

to flatten this area is measured.

Examples: Goldmann Applanation Tonometer (Figure 15), Perkins hand held

tonometer.

o Indentation Tonometers:

Measures the force necessary to indent the surface of the central cornea.

Schiøtz tonometry tends to be less accurate in myopic patients or patients with

thyroid eye disease due to poor scleral rigidty; applanation tonometry is more

accurate in these patients.

Examples: Schiøtz Indentation Tonometer (figure 16). The Tonopen (Figure 14-

right).

o Non-contact Tonometer:

Measures the jet of air needed to flatten the central cornea.

Examples: Air-puff tonometer, Ocular Response Analyzer (ORA).

32

Figure 14: different types of tonometers.

Figure 15: Goldmann applanation tonometry. A, Basic features of tonometer, shown in contact with patient‟s

cornea. B, Enlargement of A shows tear film meniscus created by contact of biprism and cornea. C, Split half

circles at beginning of applanation. D, Intraocular pressure is read when the inner half circles touch one another

(end point).

33

Figure 16: Schiøtz Indentation Tonometer. Right: Principle of indentation tonometer. A, Plunger to indent

cornea. B, Frame resting on cornea. Left: measurement of IOP by Schiøtz tonometer, the indicator on the

tonometer points to the scale readings of the tonometer. Converting from scale readings with Schiøtz tonometry to

millimeters of mercury requires a conversion table or graph.

Pachymetry

A pachymetry test is a simple non-invasive test to measure the thickness of the cornea. Normal central

corneal thickness is 520 to 540 microns, and is 630 to 670 microns peripherally.

Indications of pachymetry:

o Glaucoma screening.

o Keratoconus screening.

o Corneal evaluation prior to laser refractive surgery.

Types of Pachymeters:

o Ultrasound pachymeter (Figure 17)

Easy to use, portable.

Minimize errors of optical pachymeter (tilt)

Periphery measurements are difficult.

34

o Optical pachymeter

Slit-lamp attachment, non-portable.

Reliable.

Require experience

Inter-observer variability

More recent methods to obtain corneal thickness through Anterior segment Imaging and

analysis available:

o Technology in newer devices:

Orbscan corneal topographer

Scheimpflug camera (pentacam).

Anterior segment Optical Coherence Tomography (AS-OCT).

o advantages OF Pachymetric mapping over single measurements:

Mapping can reveal abnormal patterns such as a pellucid marginal degeneration

or keratoconus.

Allows better planning of for surgeries that include the peripheral cornea, such as

astigmatic keratotomy.

Figure 17: Ultrasound Pachymeter.

35

Lensometry

A lensemeter (Vertexometer, Focimeter) measures the power of a spherocylinderical lens, records its

optical center of the lens, the power and axis of the correcting cylinder. It can also measure the prism

and bifocal or trifocal adds to a lens. Lensometry performed on a patient's eyeglasses before refraction

can provide a starting point for the current refraction. This information is also useful in revealing

changes in refractive error. Lensometry also serves to confirm that a patient's new glasses have been

made in accordance with the doctor's prescription.

Types of Lensemeter:

o Automated and digital lensemeter: quick, easy to use and accurate (Figure 18-left).

o Manual lensemeter: are accurate but require some skill (Figure 18-right) (Appendix 4).

Automated lensemeter Manual lensemeter

Figure 18: Lensemeter.

36

Keratometry

A Keratometer (or the Ophthalmometer) measures the central curvature of the anterior cornea. It

provides an objective, quantitative measurement of corneal astigmatism, measuring the curvature. It

measures the corneal power in two meridians in diopters. These readings are called K-readings. The

average cornea has a power of 42-44 D.

Principle of keratometry

The Keratometer uses the first Purkinje image and consists essentially of a target that is

imaged by the cornea and telescoped to observe this image. It measures the size of image

reflected from corneal surface, because cornea acts as convex mirror.

The size of the image depends on the distance of the object and the curvature of the cornea.

For a fixed distance of the object the size of the image depends on the curvature of the cornea.

Similarly for a given size of the image distance of the object is different depending on the

curvature of the cornea.

Keratometry determines corneal curvature by measuring the size of a reflected “mire” (Figure

19-right). Doubling of image avoids problems from eye movements. Radius scale is

determined and diopter scale is derived from the radius using the formula for surface power

D= (n-l)/r

Where n=1.3375, the “standardized” refractive index for the cornea.

Keratometer measures only the central 3mm of the corneal diameter.

Indications of Keratometry:

o Contact lens fitting.

o IOL calculations

o Keratoconus screening

o Irregular cornea detection.

37

Types of Keratometer:

o Automated Keratometer:

Portable, stand alone or as part of newest models of autorefractometers.

Easy to use, quick and accurate.

o Manual Keratometer (Figure 19):

Several models, Bausch & Lomb is the most common model, another common

model is the javal schoitz model (Figur 19-right).

Accurate but require some training.

Operating the machine differs according to model; however the principle is to

properly align two images reflected from the anterior corneal surface in two

perpendicular meridian (details on the set-up and technique in appendix 5).

o Automated keratometry of the IOL Master/ Lenstar:

These measures the central 2.5 mm of the cornea.

About 60 data points are measured with each attempt and an averaging is done.

Accurate and reliable.

o Topographic Keratometry : when a topographic service is available, topobased K values

will aid accuracy.

Figure 19: Manual Keratometer. Left: the Keratometer machine Right: Javal Keratometer mires.

38

Perimetry

Visual field is the portion of space in which objects are visible at the same moment during steady

fixation of gaze in one direction.

Normal Visual Field

The normal monocular visual field is a slightly irregular oval, which measures, from fixation,

approximately 60° upward and 60° inward, 70° downward and 100° to 110° outward.

The field of the two eyes together or the binocular field is a combination of the right and left

monocular fields. The whole binocular field forms a rough oval extending to about 200° laterally

and 130° vertically (Figure 20).

the normal field may be considered from a practical point of view as being made up of two

portions:

The central field: that portion of the visual field within 30° radius of fixation

The peripheral field: The peripheral field makes up the remainder of the visual field

Physiological blind spot

This is an area of absolute scotoma (non-seeing area) within the boundaries of the normal visual

field, and it corresponds to the region of the optic nerve head. It is located approximately 15°

temporal to the fixation point and about 1.5° below the horizontal meridian. The normal

measurement of the blind spot is approximately 5.5mm horizontally and 7.5mm vertically.

Traquair's concept

Traquair's definition of the visual field is that it is an island of vision in the sea of Blindness. The

peak of the island represents the point of highest acuity, the fovea, while the 'bottomless pit '

represents the blind spot, the optic disc.

39

Figure 20: The binocular field of vision

We refer to Traquair's concept as the “hill of vision”, the outline of the various contours of this

hill may be projected upon a map as contour lines, which, in the nomenclature of perimetry are

termed isopters. The central point from which these isopters are measured corresponds to the

visual axis and is known as the point of fixation.

The isopters or contour lines are designated by the size and brightness of the stimulus and the

distance at which it is viewed by the observer, expressed as a fraction. Thus isopter for a 1 mm.

test object observed by the patient at a distance of 2 meters is expressed by the fraction 1/2000

and designates the specific area of the visual field within which the normal person should be able

to see this stimulus.

The visual pathways

The receptor: Is the neural epithelium of the rods and cones

The first-order neuron: Is the bipolar cell with its axons in the inner layers of retina

The second order neuron: Is the ganglion cell of the retina. Its axon passes into the nerve-fiber

layer and along the optic nerve to the lateral geniculate body.

The third-order neuron: Originates in the cells of lateral geniculate body, and then travels by

way of the optic radiations to the occipital cortex (Area 17).

40

The visual pathways thus consist of:

o Two optic nerves

o An optic chiasma

o Two optic tracts

o Two lateral geniculate bodies

o Two optic radiations

o Visual cortex on each side

Figure 21: the Visual Pathway

Principle

The nasal field represents the temporal retina and the temporal field represents the nasal retina.

In general, the fibers from the peripheral retina enter the periphery of the optic nerve, and the

fibers near the optic disc enter the central part of the nerve.

The fibers from the macular area forms the papillo-macular bundle, which has a separate course,

partial decussation occurs where the nasal fibres cross at the chiasm.

The fibers of the temporal half enter the chiasm and pass to the optic tract on the same side, and

then to the lateral geniculate body. The fibers from the nasal half enter the chiasm, decussate, and

then pass to the optic tract of the opposite side, then to the lateral geniculate body.

41

The third-order neurons pass by the optic radiation into the corresponding occipital lobe. It

follows that a lesion of the optic radiation, optic tract, or occipital lobe will cause blindness of the

temporal half of the opposite side. Projecting this outward, such lesion will cause loss of vision in

the opposite half of the visual field, a condition known as hemianopia.

Indications for visual field testing:

o Glaucoma screening and management

o Diagnosis and monitoring of retina, optic nerve and visual pathway diseases.

Methods for visual field testing:

o Clinical Methods (Appendix 6) :

Amsler grid (Central field).

Confrontation method (Peripheral field).

These methods are easy and need no special equipment, but may miss subtle

lesions

o Perimetry (systematic measurement of visual field function):

Manual (kinetic) Goldmann perimetry:

a trained examiner moves the stimulus;

stimulus brightness is held constant.

The limits of the visual field are mapped to lights of different sizes and

brightness.

Automated threshold static perimetry:

A computer program controls the test.

It keeps the size and location of a target constant.

It varies the brightness until the dimmest target the patient can see at

each of the test locations is determined.

The automated program tests the central 24° or 30° of the visual field

using a six degree spaced grid (figure 22).

Sources of error during testing for visual field:

o Machine related errors:

Calibration error.

Recording and printing results problems.

42

o Patient related problems:

Problems with positioning and comfort.

Special situation, e.g. low vision, wheelchairs.

Patient concentration problem: following instructions, errors in catch trials,

fixation losses, & fluctuation.

o Operator related problems:

Error in correcting lens (power and positioning)

Error in stimulus selection

Error in Patient preparation e.g. pupillary dilatation affects the results.

Error in test selection

Abnormal Visual Field

Three basic defects of visual fields are:

Contraction

Depression (Generalized or localized depression)

Scotoma:

o An area of partial or complete blindness within the confines of a normal or a

relatively normal visual field (i.e.). it is a defective field surrounded by a normal

field.

- Types of scotoma

Absolute scotoma: An absolute scotoma will have the same field defect

size regardless of the target size and brightness.

Relative scotoma: Relative scotoma has field defects that change with the

target size and have sloping borders that indicates an active or on going

field defect.

Positive scotoma: Patient complaints of non-seeing area (e.g.)

Central scotomata.

Negative scotoma: Examiner detects the non-seeing area (e.g.)

blind spot enlargement

- Scotomata may be unilateral or bilateral.

43

Common perimetry patterns: (figure 23)

o Retinal disease:

Rod-Cone Dystrophy (Retinitis pigmentosa): Concentric field contraction.

o Glaucoma:

Generalized depression

Enlarged blind spot

Arcuate defects

Nasal step

o Neurological diseases:

Papilledema–enlarged blind spot

Optic Neuritis –any defect possible

Pituitary Tumor –asymmetric or symmetric bitemporal defects.

Figure 22: Automated perimetry output (Above), Goldman Kinetic

perimetry output (below).

44

Figure 23: Automated perimetry defects with corresponding visual

pathway lesions.

45

Ophthalmoscopy

The Ophthalmoscopy is examination of the interior of the eye i.e. the fundus. This is usually done by

eye specialists.

Types of Ophthalmoscopy:

o Direct ophthalmoscopy: (Figure 24)

A satisfactory examination of the posterior pole (Macula & Optic Nerve) can

usually be made through an undilated pupil, provided that the media (aqueous,

lens, vitreous) are clear.

A greater extent of the peripheral posterior segment can be examined through a

dilated pupil.

Ophthalmoscopy is best done in a darkened room.

Advantages:

Greater magnification (x15)

Easier to use with small or undilated pupils

Mechanically easier to use (handheld device).

o Indirect Ophthalmoscopy:

The Indirect binocular Ophthalmoscope with +20 D lens (Figure 25-right):

a head-mounted, prism-directed light source is used coupled with use of

double aspheric (+14, +20, or +28) diopter condensing lenses to see an

inverted retinal image.

Allows binocular vision and depth perception.

Wider field of view of a given retinal area.

Easy to use in the operating room.

Better view of the periphery of the fundus (with scleral indentation).

Strong illumination.

Slit lamp Biomicroscopy: (figure 25-left)

By +78 or +90 D lens (figure 20-right)

Easy with undilated pupil and convenient to both doctor and patient.

Best for examining the macula and posterior pole.

46

Figure 24: Direct Ophthalmoscopy.

Slit lamp Biomicroscopy indirect ophthalmoscopy lenses

Figure 25: Indirect ophthalmoscopy.

47

Objectives

By the end of this chapter the student will be able to:

Recognize different ophthalmic imaging equipment.

Describe the application of each test in clinical settings

Overview

Common Ophthalmic imaging techniques that will be discussed in this chapter includes:

External eye and slit lamp photography

Ocular Ultrasound and IOL calculation

Corneal topography

Fundus photography

Optical coherence tomography (OCT)

Slit lamp photography

Slit Lamp Photography is a specialized ophthalmic imaging technique used for imaging the

anterior segment of the eye. An adapted slit lamp is used with a camera or video imaging

system connected to capture the image created; the image is then usually saved to by special

software.

Ophthalmic Imaging

48

Photo slit lamps available today may be film based or digital. Desirable features include coaxial

viewing (viewing and photography through the same lens system) and a flash source for both

the slit and diffuse illuminators.

Slit lamps not designed for photography may produce reasonable photographs with the proper

add-ons. Of these additions, electronic flash illumination is the most important to provide the

short exposures required to „hold‟ eye movements. Another important accessory for a non-

photographic slit lamp is a diffuse illuminator to provide overview photos of the anterior

segment.

Recently smartphone cameras were used in combination with conventional slit lamp to perform

the same function in case of lack of the mounted slit lamp camera with some success.

Ophthalmic Ultrasound

Ultrasound is a necessary tool in medical imaging and plays an important role in ophthalmologic

diagnoses. It is the most important imaging technique in eyes with anterior segment opacities.

Ultrasound is an acoustic wave with a frequency greater than 20 kHz. The frequencies used in

diagnostic ophthalmic ultrasonography are 8 to 25 MHz for imaging the posterior segment of the eye

and orbit and 50 MHz for imaging the anterior segment.

Indications of Ophthalmic Ultrasound:

o For the anterior segment

In opaque media: for detection of Cataract or Dislocated / subluxated lens.

In clear ocular media: for diagnosis of iris and ciliary body tumours

o For the posterior segment

In opaque media: detection of

vitreous hemorrhage

retinal detachment

intraocular foreign body

In clear ocular media:

Tumors (size/site/post-treatment follow-up)

RD

49

o Biometry

Pre-operative scanning is done to determine IOL power (Ocular biometry).

Post-operative verification is done to determine the eye length when the

refraction differs from surgeon's expectations.

o Orbital examination

Exophthalmos

Palpable orbital mass

Principle:

o It is based on the physical principles of pulse-echo technology:

It uses piezoelectric crystal transducers to produce ultrasonic wave-front pulses

and recover echoes for electronic display and processing.

The sound waves, like light waves, pass through certain tissues and are reflected

by others. When the sound wave meets firm tissue, the waves are reflected off its

surface.

The longer an impulse takes to return, the further it is placed on the display. This

time can be converted to distance with a known speed of sound in the tissue

through which the sound is traveling. Each tissue has a characteristic speed at

which the sound travels through it. The height of the spike on the graph relates to

the intensity of the returned echo.

o The frequency most commonly used in ocular imaging is 10 MHz. the higher-frequency

ultrasound provides higher resolution with decreased penetration. The maximum

penetration that can be achieved for a 10 MHz system is approximately 50 mm. For a

60 MHz system, penetration is only 5 mm.

o The rebounding waves are received by a transducer, which turns the sound energy into

electrical impulses that are amplified and displayed on an oscilloscope in a visible

pattern called an ultrasonogram or echogram.

Types of Ophthalmic ultrasound:

o A-scan ultrasound (Ocular biometry)

A-scan is a single-beam, linear wave that is directed in a probing manner to detect

interference along its pathway (Figure 26).

It is used in combination of B-scans and to measure the axial length of the eye

(length of the eye from front of cornea to front of retina in mm) in IOL calculation

(Biometry) (see Appendix 7 for more details on ocular biometry and IOL

calculation).

50

o B-scan Ultrasound:

Ultrasound Image of the eye allowing imaging of the vitreous, choroid, and retina.

A B-scan consists of a series of A-scan impulses sent out by a moving transducer

that are combined into a two dimensional image.

This minimizes possible missed areas and gives a clearer picture of the underlying

pathologic condition.

Homogeneous tissue, such as normal lens vitreous or aqueous humor, does not

reflect ultrasound and produces no echoes (figure 27-left).

Retina and sclera gives high amplitude echoes which is seen in the 2 D image.

B-scan is useful in posterior segment evaluation such as in cases of retinal

detachment, vitreous hemorrhage, intraocular tumors and foreign body, posterior

uveitis and scleritis (figure 27-right).

Figure 26: A-scan Ocular Ultrasound.

51

Normal B-scan Ultrasound Retinal detachment

Figure 27: B-scan Ocular Ultrasound.

Corneal Topography

Topography provides a color-coded representation of the cornea‟s shape and monitors corneal

curvature changes from the apex to the periphery.

Principle:

o It is based on the principles of keratometry and photokeratoscopy combined with the

capability of modern computers and software technology.

o It accurately analyzes the radius of curvature (mm) and corresponding refractive power

(diopter) at 6000–8000 points on the corneal surface from inside the 1 mm optical zone to

outside the 9–11 mm optical zone.

o a complete color-coded map is obtained (figure 28):

Cool colors such as blue and green represent flatter areas of the cornea

Warmer colors of orange and red represent steeper areas.

o Newer machines like Orbscan or Pentacam are able to provide a map of the anterior and

posterior cornea, white to white measurement, anterior chamber depth and corneal

pachymetry:

The Orbscan:

It takes multiple cross-sectional scans of the cornea with an advanced

placido disc system

It is able to analyze:

a. The elevation and curvature measurements on both the anterior and

posterior surfaces of the cornea

52

b. White to white measurement

c. Anterior chamber depth

d. Angle kappa

e. Corneal pachymetry values.

Galilei G2:

It merges two technologies – the rotating Schempflug and the Placido– into

one measurement, leading to accurate values of the posterior and anterior

surfaces.

The dual Scheimpflug approach offers very accurate pachymetry readings

and needs to rotate only 180 degrees.

The Oculus Pentacam (Figure 29):

It is a rotating Scheimpflug camera that generates Scheimpflug images in

three dimensions, with the dot matrix fine-meshed in the center due to the

rotation.

It takes a maximum of 2 seconds to generate a complete image of the

anterior segment.

Any eye movement is detected by a second camera and corrected in the

process.

The topography and pachymetry of the entire anterior and posterior

surfaces of the cornea from limbus to limbus are calculated.

The analysis of the anterior eye segment includes calculation of the

chamber angle, chamber volume and height.

Images of the iris, anterior and posterior surfaces of the lens are also

generated. The densitometry of the lens is automatically qualified.

Value:

o The topographic maps provide the ability to monitor corneal curvature changes from the

apex to the periphery that helps in:

Pre-operative preparation for refractive surgery.

Screening and diagnosis of a corneal pathology.

Contact lens fitting.

53

Most corneal topographer systems available today can generate various map displays, the most

commonly used maps include the following:

o Axial or sagittal map (Figure 29):

The most widely used and simplest of all topographical displays.

It shows the curvature of the anterior surface of the cornea as a topographical map

in dioptric values and measures it in axial direction relative to the center.

The analysis should include the keratometric values and should not be interpreted

based on the colors alone.

o Elevation maps (Figure 29):

This is the difference in height between the measurements of the cornea and a

reference shape called best fit.

This value can be negative if the measurement is below the reference and positive

if it is above the reference.

The reference shape could be a best-fit sphere, best-fit ellipsoid, or a toric

reference shape.

Other types of topography displays include a tangential map, true net power, refractive map,

keratometry map, Multiview map, differential map, photokeratoscopic view, profile view, etc.

Figure 28: corneal topography.

54

Figure 28: Oculus Pentacam, normal four-map selectable showing: (top left) anterior elevation, (top right)

posterior elevation, (bottom left) sagittal, and (bottom right) pachymetry (corneal thickness).

Fundus Photography

Fundus photography involves capturing a photograph of the back of the eye i.e. fundus. Specialized

fundus cameras that consist of a complicated microscope attached to a flash enabled camera are used

in fundus photography. The main structures that can be visualized on a fundus photo are the central

and peripheral retina, optic disc and macula (Figure 23). Fundus photography can be performed with

colored filters, or with specialized dyes including fluorescein and indocyanine green.

Indications of Fundus photography:

o Documentation and monitoring of retinal and optic nerve conditions e.g. Papilledema,

Optic nerve cupping in glaucoma… etc.

o Aid in diagnosis and follow up of retinal, and choroidal diseases e.g. Retinal vascular

disease, posterior uveitis, Macular degenerations, Intraocular tumors.

55

Intravenous Fluorescein Angiography (IVFA):

o It is a diagnostic test that is used to capture the blood flow in the back of the eye,

allowing physicians to diagnose different types of retinal disease.

o Principle:

For fluorescein angiography, a fundus camera must be equipped with a rapid-

recycling, high-output power supply and an exciter and barrier filter

combination.

The exciter filter is placed in the path of the light and allows only a specific

wavelength of blue light (approximately 490 nm) to strike the fundus.

When fluorescein is introduced into the circulation of the eye, the blue light

excites the fluorescein molecules to a higher state of activity, causing them to

emit a greenish-yellow light of a higher wavelength (approximately 520 nm),

creating the fluorescence that we record.

The barrier filter is positioned to filter out the blue exciter light and allow only

the excited yellow-green light of actual fluorescence to strike the image sensor.

o It is particularly helpful in the diagnosis and management of Diabetic Retinopathy,

Macular Degeneration, and Vein/Artery Occlusions.

o Phases of IVFA: (Figure 24) (steps of the procedure in Appendix 8)

Early phase: 10-20 seconds after injection, choroidal circulation appear in this

phase as well as the transit of blood flow from arteries to veins.

Middle phase: 1-2 minutes after injection, the fluorescein dye fills the veins and

then its brightness starts to fade away

Late phase: after 3 minutes from injection, shows elimination of the dye from

the eye gradually.

Sources of Error or hazards during Photography:

o Factors related to the patient:

Poor dilatation of the pupil

Media opacity (corneal or lenticular opacity)

Uncooperative patient (Excessive blinking, poor centration or alignment)

o Factors related to the dye:

Extravasation of the dye (improper injection into vein)

Side effects (nausea/ vomiting).

Rash and dermatitis.

Dark color of sweat and body fluids.

Allergic reaction (most serious).

56

o Factors related to the machine:

Dust/material on lenses.

Shutter/synch off.

Software problems.

o Factors related to the operator:

Improper focus-eyepiece; too close/not close enough

Inappropriate filtration

Wrong flash setting or capture speed for best image

Figure 23: Fundus photography.

57

Figure 24: Fluorescein Fundus Angiography (early and late phases).

Optical Coherence Tomography

Optical Coherence Tomography (OCT) (figure 25) is a diagnostic imaging device that provides

non-contact direct high-resolution cross-sectional images of the retina (Axial resolution 1–

15 µm) to aid in the clinical evaluation and detection of macular and optic nerve diseases.

Principle:

o OCT is an optical imaging technique that uses light instead of sound, so the optical

imaging is limited to tissues that are optically assessable.

o OCT performs cross-sectional imaging by measuring the time delay and intensity of

back-scattered or back-reflected light from structures inside tissue

o The OCT images and analyzes macular thickness, the retinal nerve fiber layer and the

optic disc utilizing low-coherence interferometry, which permits the measurement of

tissue within 10 microns (µm) resolution.

o The instrument rapidly scans the retina with an 820nm near infrared light beam from a

diode. The delay of the light echo back-scattered from different layers in the retina is

used to determine the retinal and nerve fiber layer thickness.

Applications of OCT in ophthalmology:

o Anterior segment imaging: An anterior segment OCT can image the anterior structures

of the cornea, measure the corneal thickness, and allow visualization of the anterior

chamber angle and related internal structures.

o Posterior segment imaging: Imaging of the retina can evaluate the optic disc, nerve fiber

layer, vitreoretinal interface, and macula.

o The high-resolution images allow for a diagnosis and monitoring of glaucoma, an

58

epiretinal membrane, cystoid macular edema, macular hole, macular degeneration,

macular complications of diabetic retinopathy, and other conditions.

o A measurement of the thickness of the nerve fiber layer is a diagnostic indicator for

early glaucoma and disease progression. These values are compared over time to

analyze the patient‟s individual measurements to reference values of a normative

database.

o OCT imaging is useful in determining the effectiveness or adequacy of treatment in

disease conditions like glaucoma, macular edema, central serous retinopathy, macular

holes, and exudative age-related macular degeneration.

Role of technician regarding OCT machine:

o There are many OCT devices with variable software and hardware, but the basic

principles are similar.

o Proper training should come from the distributor of the machine if it is brand new or

from a knowledgeable in-house technician if the machine was in work for a while.

o The role of ophthalmic assistant or technician is to care for the machine properly

according to the general and the manufacturer‟s rules and may perform the scan

according to the establishment‟s policy and regulations.

Normal Macular OCT scan Optic nerve head OCT scans

Figure 25: Optical coherence tomography (OCT).

59

Figure 25: Above: OCT of Pigment epithelial detachment in Exudative Age related macular degeneration Below:

OCT of Cystoid macular edema with subfoveal neurosensory retinal detachment.

60

Ophthalmic Medical Assisting, An Independent Study Course, E. Newmark & M.A.

O’Hara, 6th Edition, 2012, AAO.

The Ophthalmic Assistant, 9th Edition, H.A. Stein, R.M. Stein and M.I. Freeman, Eighth

Edition, 2013, Elsevier Inc.

Fundamentals for Ophthalmic Technical Personnel, B. Cassin, 1995, W.B. Sanders

Company.

Clinical Optics, 3rd

edition, AR. Elkington et al., 1999, Blackwell Science, Tokyo, Japan.

Introducing ophthalmology: a primer for office staff. American Academy of Ophthalmology,

2013.

Duane's Clinical Ophthalmology, W. Tasman, & EA. Jaeger (Eds.), 2007 Ed. New York:

Lippincott-Raven.

Delmar's comprehensive medical assisting: administrative and clinical competencies. Lindh,

Wilburta Q., Marilyn Pooler, Carol D. Tamparo, Barbara M. Dahl, and Julie

Morris. Cengage Learning, 2013.

Today's Medical Assistant: Clinical and Administrative Procedures. Bonewit-West, Kathy, Sue

A. Hunt, and Edith Applegate. Elsevier Health Sciences, 2012.

Practical Ophthalmology-A Manual for Beginning Residents, 7ed. American Academy of

Ophthalmology, 2015.

Book Coordinator ; Mostafa Fathallah

General Directorate of Technical Education for Healt

لىصاسج الصحح والسكاى وحزس تعهحقىق الشش والرألف

Biblography and Recommended Readings

61

Appendix 1 - Testing Acuity for Patients with Low Vision

1. If the patient is unable to resolve the largest optotype on the distance acuity chart from the

standard testing distance, ask the patient to stand or sit 3 meters from the well-illuminated test

chart.

2. A projected chart is less desirable to use in this situation than a printed wall chart. A low-

vision test chart, if available, is preferable for these patients.

3. Occlude the eye not being tested.

4. Repeatedly halve the testing distance (up to 1 meter) and retest the distance visual acuity at

each stage until the patient successfully identifies half the optotypes on a line.

5. Note the corresponding acuity measurement shown at that line of the chart.

6. Record the acuity value for each eye separately, with correction and without correction, as

would be done for standard distance acuity testing, recording the distance at which the patient

successfully reads the chart as the numerator of the Snellen acuity designation; for example,

5/60.

7. If the patient is unable to resolve the largest optotypes on the chart from a distance of 1 meter,

display 2 or more fingers of 1 hand and ask the patient to count the number of fingers

displayed. Record the longest distance at which counting is done accurately; for example, CF

at 50 cm.

8. If the patient cannot count fingers, move your hand horizontally or vertically before the

patient at a distance of approximately 50 cm. Record the distance at which the patient

reported seeing your hand movement; for example, HM at 50 cm. If the patient cannot detect

your hand motion, shine a penlight toward the patient's face from approximately 30 cm and

turn it on and off to determine if light perception is present.

9. If the patient cannot see the light, dim the room lights and shine the brightest light available

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(usually the indirect ophthalmoscope) toward the patient's eye again. If the patient cannot see

even the brightest light, record the response as NLP (no light percept ion). If the patient can

see the light, record the response as LP (light percept ion). No record of distance is required.

10. If light is perceived from straight ahead, move the light sequentially into each of the 4

quadrants of the visual field. Turn the penlight on and off in each field, and ask if the patient

can see the light. If the patient correctly identifies the direction from which the light is

coming, record the response as LP with projection. Specify the quadrant(s) in which light

projection is present. If the patient is unable to identify any direct ion but is able to discern

light in the straight-ahead position, record the response as LP without projection.

11. If the light can be seen from straight ahead, colored filters can be placed in front of the light

and the patient is asked to identify the color of the light. Record whether color percept ion is

present.

12. Repeat steps 1-10 for the fellow eye, as appropriate.

Appendix 2 – Color vision testing

1. Evaluation of color vision is often performed with pseudoisochromatic color plates.

2. The patient should wear glasses during color vision testing if they are normally worn for near

vision.

3. Each eye is tested separately.

4. Patients are instructed to look at a book of these plates, which display patterns of colored and

gray dots.

5. The color plates are presented consecutively under good illumination, preferably natural light.

6. Patients with normal color vision can easily detect numbers and figures composed of, and

embedded in, the multicolored dots.

7. Patients with color vision deficits cannot distinguish the numbers and figures.

8. Results are recorded according to the detailed instructions provided with the plates. Usually, a

fraction is specified, with the numerator equivalent to the number of correct responses and the

denominator the total plates presented.

9. The type of color defect can be determined by recording the specific errors and using the

instructions provided with the plates.

10. Various combinations of colors are used to identify the nature of the color vision deficit.

Appendix 3 – Technique of Tonometry

1. Technique of Schiøtz tonometry:

o After the instillation of local anesthesia, such as one drop of Benoxinate, the patient is

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placed in a supine position and asked to look directly upward.

o The physician separates the lids to keep them from contacting the eyeball, taking care not

to exert pressure on the globe.

o The instrument is placed gently in a vertical position directly over the cornea, and the

plunger is allowed to exert its full weight.

o With the instrument held steady, the pointer will stay fixed at a single scale, with slight

oscillations 0.5 mm in either direction because of alterations in the internal pressure caused

by the arterial pulse in the eye.

o If the reading with the 5.5-g weight is between 3 and 6 on the scale, this reading may be

used. Readings below 3 with this instrument are inaccurate, and a 7.5-g weight should be

added and the reading taken again.

o If the reading is still below 3, the 10-g weight should be used.

o If the patient squeezes his or her lids, this will raise the IOP; note should be made of this,

because a falsely high pressure may be recorded.

2. Applanation tonometry:

o This very accurate method for measuring IOP may be performed with a Goldmann

applanation tonometer mounted on a routine slit lamp biomicroscope or with a handheld

applanation tonometer (Perkins Tonometer).

o After local anesthesia is introduced, fluorescein paper strips are inserted into the lower

conjunctival sac to place dye in the tear film.

o The tonometer scale is set at 10 and the head is then brought gently against the anterior

corneal surface with the patient looking straight ahead.

o On contact and with the cobalt blue light in place, two fluorescein semicircles are seen

through the microscope, one higher than the other; the top with the outer curve up and the

bottom with the outer curve down.

o The semicircles should be equal in size and in the middle of the field of view. Their steady

pulsation indicates that the instrument is in the correct position.

o Pressure on the eye is increased by turning the calibrated dial of the tonometer until the

inner border of each semicircle just touches and overlaps with each pulsation.

o The pressure reading is determined directly by reading from the measuring drum and

multiplied by 10 (in mm Hg).

3. The Tonopen:

o It is an electronic tonometer that has its greatest use in patients with corneal scarring or

altered corneal shape such that conventional Schiøtz or applanation tonometers cannot be

employed with any accuracy.

o The soft tip of a blunt pencil-like device connected by wire to an electronic recorder is

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quickly touched to the anesthetized cornea.

o Pressure is calculated by the jump in scale readings from baseline noncontact curve to that

of the momentary touch flattening the cornea or indicated directly on a digital screen.

o The tonopen is portable and battery operated, but expensive to buy.

4. The air puff noncontact tonometer:

o It is a reasonably accurate electronic tonometer.

o It has the advantage of use without topical anesthetic.

o The patient sits with the head in a slitlamp-like device, and a 3 ms (millisecond) puff of air

(a blink takes 10 ms) is blown against the cornea.

o The indentation pattern is detected by the tonometer eye.

o The pressure is calculated by the amount of corneal flattening by the fixed air puff pressure

and displayed on digital readout.

o This machine can be used in glaucoma-screening programs.

Appendix 4 – Manual Lensometry

o The lens to be measured is placed on the lensometer stage, and the power wheel is turned

until the target mires are in focus.

o The mires cross each other at right angles; there are three lines in one meridian and one in

the other (Figure below).

o If the mires all focus simultaneously at a given power, no cylinder is present and the lens is

completely spherical. The power is read directly off of the power wheel.

o The second wheel on the lensometer is an axis wheel, which can be rotated to turn the

mires until they are lined up along the principal meridians of a lens containing a cylinder.

o Alignment is correct when the crossing lines are perfectly straight (not broken).

o The power wheel is then turned to focus the strongest plus power of the lens (single line

meridian). When this is focused using the greatest plus power (or least minus power), the

spherical power component is recorded.

o The power wheel is turned again to bring the weaker (more minus) meridian into focus

(three-line target) and the cylindrical power component is noted as well as the axis of that

meridian, which is read directly from the axis wheel.

o The lens prescription is the strongest plus power minus the difference in power between

the two settings, and the axis of the cylinder is that of the more minus meridian, as

indicated on the axis of the wheel.

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Photo credit: Ophthnotes.com

o Example 1 of lensometer calculations

Strongest plus meridian reading: +5

Weaker plus meridian reading: +3.50

Axis of weaker meridian: 80 degrees

Final power: +5 / -1.50 @ 80 degrees.

o Example 1 of lensometer calculations

Strongest plus (weakest minus) meridian reading: -3

Weaker plus (stronger minus) meridian reading: -4

Axis of weaker plus meridian: 40 degrees

Final power: -3 / -1 @ 40 degrees.

o Plus cylinder prescriptions are less frequently used, but may be done by reversing the

above technique. For example:

Weakest plus meridian: +2

Strongest plus meridian: +3.50

Axis of strongest plus meridian: 50 degrees

Final power: +2 / +1.50 @ 50 degrees.

o Conversion of minus cylinder prescriptions to plus or the opposite is carried out by

reversing the sign of the cylinder, adding the difference between the two lenses, and adding

90 degrees to its axis, e.g., +3 / -2 @ 20 degrees converts to +1 / +2 @ 110 degrees.

o Prism power is measured in the lensometer by reading the amount of decentration from the

optical center cross mires. This is determined by counting the number of circles or lines on

the eyepiece reticule away from center (figure below).

For ground in prism, base-in is noted if the power center is located on the nasal side

of the lens; base-out is noted if temporal.

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For induced prism, the difference between the patient's pupillary distance and the

lens optical centers determines the amount of induced prismatic effect. Prentice's

rule calculates the amount of induced prism.

Appendix 5 – Manual keratometry

The object used is an illuminated circle with plus and minus images as shown in figure (figures below).

The two prisms inside the instrument give two additional images one displaced horizontally and another

displaced vertically. Three images are seen as in figure while taking the reading the pluses and minuses

coincide.

Keratometer set-up

1. Focus the eye piece

- Set the adjustable eye piece so that it extends as for as possible

- Place a white paper in front of the instrument objective to retro

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- illuminates the reticle

- Adjust the eye piece until the reticle is first seen in sharp focus

2. Ask the patient to remove his glasses

3. Adjust height of chair and instrument to a comfortable position for both patients and examiner

4. Unlock instrument controls (B& L. Keratometry)

5. Instruct patient to palace his chin in the chin rest and forehead against the forehead rest

6. Raise or lower the chin rest until the patient‟s outer canthus is aligned with the hash mark on

upright support or the pointer on the side of the instrument

Step- by-step procedure

1. From outside the instrument, roughly align the telescope with the patient‟s eye.

2. Instruct the patient to look at the image of his eye in the keratometer.

3. Look into the keratometer and align it by moving it from side to side or up and down until you can

see the image of the mires (circle with plus and minus) on the patient‟s cornea.

4. Focus the mires and align them with the reticle in the lower right and head circle.

5. Lock the instrument (B&L Keratometer only).

6. Adjust horizontal and vertical power wheels until mires are in close apposition.

7. Rotate the telescope to align spurs ( plus and minus signs) on the mires to 2 major meridians of the

patient‟s cornea.

8. Adjust the horizontal power wheel until the vertical mires are co-incident.

9. Adjust the vertical power wheel until the horizontal mires are co- incident.

10. Readjust focus and / re-center reticle as needed.

11. When mires are not clear lubricating drops can be used aand Keratometry can be performed again.

Recording

1. Recording for each eye separately

2. Record the power and meridian for horizontal meridian first (the primary meridan)

3. Write a slash mark after the primary meridian and record the power and meridian for the vertical

meridian (the secondary meridian)

4. Record the amount of corneal astigmatism in diopters

5. Record the type of astigmatism:

WR-With the rule

AR-Against the rule

OBL-Oblique

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6. Record the conditions of the mires e.g. MCAR- Mires Clear And Regular / MIAD- Mires Irregular

And Distorted

Example:

OD 42.50 at 180/ 43.50 at 90; 1.0D WR,MCAR

OS 47.37 at 180/ 41.37 at 90; 6.0D AR, Mires distorted

OD 41.75 at 180 / 43.75 at 70; 2.0D irregular astig; mires distorted

OS 43.12 at 135 / 41.87 at 45; 1.25D OBL; MCAR

OD 42.00/43.00 at 90; 1.0D WR MCAR

OS 42.00/42.00 at 90; sphere MCAR

(Meridia are expected to be 90 degree apart; therefore if only the meridian is recording the position of the

other can be assumed to be 90 degrees away).

To obtain proper focus, rotate the focus knob until the bottom-right circles converge to form a fused

image.(figure below)

To locate the proper axis, rotate the keratometer until the pluses between the two bottom circles are in the

same plane.(fig 10.8)

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Appendix 6 – Perimetry

Confrontation method

The confrontation field test compares the boundaries of the patient‟s field of vision with that of the

examiner, who is presumed to have a normal field. It is a rough, but very useful clinical test, which

should be applied in every case, if there is any suspicion of a defect in visual field.

Performing the confrontation test

o Seat the patient at a distance of 2 to 3 feet from you. Confront (face) the patient, cover or

close your left eye, and have the patient cover the right eye. You and the patient should fixate

on each other's uncovered eye

o Extend your arm to the side at shoulder height and slowly bring two fingers from beyond

your peripheral vision toward your nose into the field of vision midway between the patient

and yourself. Ask the patient to state when the fingers are visible

Repeat the process of moving fingers into the visual field from four different directions. If

you picture a clock face in front of the patient's eyes, you perform the hand movement from

about 2 O'clock, 4 O'clock, 8 O'clock, and 10 O'clock, each time bringing the fingers toward

the center of the clock face

o The patient should see the fingers at the same moment you do in each of the four quadrants

(upper-left, upper-right, lower-right and lower-left quarters) of the visual field. (Note: A

quadrant of vision described from the patient's point of view). If the patient does not see your

fingers at the same time you do, the breadth of patient's visual field in that quadrant is

considered to be smaller than normal and additional perimetric studies are performed

o Record the patient's responses in the patient's chart by indicating simply that the visual field

is comparable to yours or that it is reduced in any of the four quadrants for that eye

o Repeat the procedure as described with the patient's other eye and record the results similarly

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Tangent Screen (Bjerrum screen)

Estimation of defects of central fields using tangent screen is termed as campimetry or scotometry. It

is done to evaluate the central and para central area (30 degree) of the visual field. The tangent screen

is 1 metre or 2 metres square. Accordingly the patient is seated at a distance of 1m or 2m

respectively.

The screen has a white object for fixation in its centre, around which are marked concentric circles

from 5 degree to 30 degree. The patient fixates on the central dot with one eye occluded.

A white target (1-10 mm diameter) is brought in from the periphery towards the centre in various

meridians. Initially, the blind spot is charted, which is normally located about 15 degree temporal to

the fixation point on a 1 m tangent screen. It will fall outside the 1m tangent screen at 2m. Doubling

the testing distance and doubling the target size will double the scotoma size.

Note: Fixation targets should be capable of variation from 1 to 100 mm. Circles of varying size are

used for fixation when testing for small central scotomas

White tape may be attached to the two upper corners of the screen so that they cross in the center

when testing the large, dense, central scotomas. The patient fixates where they think the tapes will

cross even though they cannot see the actual crossing point

Performing the tangent screen examination

o For a tangent screen examination, it is essential that the patient wears his glasses if he has a

refractive error. This is not essential in perimetric examinations

o The examiner usually stands to one side and keeps his/her eye on the patient's eye to ensure

that the fixation is absolutely maintained

o The test object, the size of which is correlated with the patient's visual acuity, is moved from

the periphery towards the centre

o The patient indicates when they see the test object either by making a verbal response, such

as ''yes'', or by tapping a coin

o At all times the fixation of the patient should be checked

o The easiest way is to map out the patient's blind spot first, which is smaller and closer to the

fixation point

o Check the patient's responses by rotating the test object out of view so that it is not visible to

the patient at all

o Be careful when transferring the information from the felt screen to the chart because errors

can occur

o Make sure you understand the proper degree of eccentricities and meridian placements on the

stitched chart and the recording diagrams

o Mark the areas of scatter with a cross hatch and record the target size

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o Evaluate each scotoma for depth with smaller and larger targets

Amsler grid test

The Amsler grid test determines the presence and location of defects in the central portion of the

visual field. The Amsler grid is a printed square of evenly spaced horizontal and vertical lines in a

grid pattern, with a dot in the centre. The chart grid and dot may be either white on a black

background or black on a white background.

Performing the Amsler grid test

o Have the patient hold a white-on-black test card about 16 inches away with one hand and

cover one eye with the other hand, an occluder, or a patch

o Direct the patient to stare at the centre dot and to report if any portions of the grid are

blurred, distorted, or absent. The patient should not move the gaze from the centre dot, so

that the presence of any distortion can be assessed

o If they answer yes, you may repeat the test with black-on-white Amsler recording chart, on

which you ask the patient to mark the location of visual difficulties.

o If test results are normal, state so in the patient's record. If abnormal, state so, and include

the Amsler recording chart in patient's record. The patient with abnormal findings is a

likely candidate for further studies. The patient may also repeat this convenient procedure

independently at home and report changes to the ophthalmologist's office (the patient

should perform the test monocularly, always at the same 16-inch distance and under the

same illumination)

Perimeters

The screen may be either an arc or a bowl of a radius of 330 mm.

Lister's perimeter: A rotatable arc, capable of being revolved round a pivot, and along which a

test object can be moved.

Goldmann perimeter:

o A hemispherical bowl over which a target (a spot of light of adjustable size and

illumination) can be directed.

o The Goldmann perimeter is more standardised and preferable for glaucoma examinations,

as, both the central and peripheral visual fields can be recorded.

o The targets of the perimeter consists of circular white discs (or a spot of light) of diameters

ranging from 1-10 mm. The isopters represent the limits of the field of vision with each

target, and are accordingly labeled 1/330 (1 mm target at 330 mm distance, the radius of

perimeter), 2/330. 10/330, etc.

o Coloured discs or coloured spots of light are especially used for estimation of a differential

field loss to colour. In normal conditions, the blue field is largest, slightly smaller is the

white, and then followed by the yellow, red and green.

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Automated perimeter

Automated perimetry was developed to standardize visual field testing and to increase the

reliability of visual tests. Various manufacturers make automated perimeters based upon

computerized projection systems and a LED (light emitting diodes) system. Automated perimeters

can perform screening and diagnostic field tests and can use kinetic and static methods. These

perimeters are most often used for static threshold testing.

The most widely used automated perimeter is the Humphrey Field Analyzer which has become the

standard for visual field testing.

Appendix 7 – Tips on Ocular biometry

Handling a scan

o Always check the instrument before usage

o Wash and dry hands before working

o Administer 1 drop of Benoxinate anesthetic eye drops.

o Allow 2 to 5 minutes for the local anesthetic to act

o Explain to the patient that you will be touching his/her eye with an instrument, but they

will not feel it. Ensure them the instrument will not hurt the eye

o Applanate the cornea using the hand held ultrasound transducer probe. This is repeated

three times.

o Ask the patient to look straight ahead (for IOL power calculation)

o Record the readings for each eye separately in the patient's chart

The technicians role is to

o Explain the procedure and its importance to the patient in their language

o Reassure the patient, if the patient is uncooperative

o Communicate well with the patient to reduce anxiety and clear their doubts

o Be gentle while applanating the cornea for A scan- too much pressure will give inaccurate

measurement

o Handle equipment with care

Maintenance

o Keep the instrument covered when not in use

o The instrument can be cleaned with a soft clean cloth

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Appendix 8 – Fluorescein Angiography

To produce an angiogram the following steps are recommended:

1. Set the image capture software to record for fluorescein angiography. This will set the camera and

computer to process the image in black and white, and it also raises the ISO setting, since the

fluorescein filters absorb a lot of light.

2. Set the flash intensity to the level used for color photography.

3. Introduce the green or „red-free‟ filter into the light path.

4. Position the patient at the camera and take a stereo photograph of the area to be studied with the

green filter in place.

5. Set the image capture software and the camera to its fluorescein angiography settings. This may

automatically increase the flash output to the level required for fluorescein angiography, or you

may have to do these setting changes manually.

6. When the needle is correctly inserted into the patient‟s vein, check the patient‟s head position and

viewing through the camera‟s viewfinder, to again ensure proper alignment and focus.

7. Initiate the rapid injection of the fluorescein and simultaneously activate the timer.

8. At 5–7 seconds following the start of the injection, the exposure sequence should commence. The

average arm-to-retina circulation time in an adult is between 8 and 15 seconds. In a child, it can

occur within 4–7 seconds and requires earlier initiation.

9. After the rapid-sequence documentation of the initial circulation of fluorescein through the full

arteriovenous phase, the frequency of exposures may be reduced considerably since further

development in the angiographic pattern will occur much more slowly beyond this point. (An

understanding of the hemodynamics of the choroidal and retinal circulation, as well as the

appearance of fluorescein angiographic characteristics of the various lesions studied, will improve

judgment.)

10. Intermediate or recirculation phase: photographs should be taken at approximately 1–3 minutes

after injection.

11. A late photograph, approximately 8 minutes after injection, is also recommended. Certain

conditions are not delineated until this point and the time interval can also be used to monitor the

patient for any signs of adverse effects from the fluorescein angiographic procedure. Stereo

fluorescein photography can be incorporated at any stage of the angiogram by use of the procedure

described for stereo photography.