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Does refractive surgeries (PRK VS.

LASIK) reduces the Contrast

Sensitivity while enhancing the VA?

TOKA ALMINYAWY

Supervisor:

NOHA ALSALEEM.

2015‏

OPTOMETRY DOCTOR

APPLIED MEDICAL SCIENCE

KING SAUD UNIVERSITY

Does refractive surgeries (PRK VS. LASIK) reduces the Contrast Sensitivity while enhancing the VA?

1

Aknowledgement

I thank all my family and friends who supported me through all my studying

years, through ups and downs, i wouldn’t be anything without you.

Special Thanks

MS. Noha Alsaleem , you was my guidance , i appreciate your efforts,

without you this project wouldn’t see the light.

Gratufully, your student.

Toka


2

Didication

DAD

My guardian , Mentor and Protector, you created the passion for me to enter this

major, i didicate all my success to you honor,

You had a vision i will make it true, because i am sure when you don’t have my

hands, you have my back..

For All these times you stood by me

For all the joy you brought to my life

For all the wrong you made right

For every dream you made come true

You are the who held me up

Never let me fall

You were my strength when i was weak

Lifted me up when i couldn’t reach

You gave me faith cause you believed

You said no star was out of reach

Im grateful for each day you gave me

Maybe i don’t know that much

But i now this much is true

I was blessed because i was born by you..


3

MOM

spending every moment in my life wouldn’t be enough, you are the cause of

my presence, may you live in joy infinity .

you were always there for me

the tender wind that carried me

a light in the dark shining your love into my life

you have been my inspiration

through the lies you were the truth

my world is a better place because of you..


4

Table of Contents

ABSTRACT ..................................................................................................................................... 3

CHAPTER ONE :

1.1 INTRODUCTION ......................................................................................................................... 8

1.2 LITERATURE REVIEW .................................................................................................... 10

CHAPTER TWO :

2.1 METHODOLOGY .................................................................................................................. 15

2.2 MATERIALS ........................................................................................................................... 16

2.3 CONTRAST SINSITIVITY TESTING ............................................................................. 18

CHAPTER THREE:

3.1 RESULTS .................................................................................................................................. 25

3.2 DISCUSSION ............................................................................................................................ 36

3.3 STUDY LIMITATIONS .......................................................................................................... 37

CHAPTER FOUR:

4.1 CONCLUSION ........................................................................................................................ 38


5

REFERENCES .............................................................................................................................. 40

INDEX ............................................................................................................................................. 44

Concent of participation and agreement INDEX ........................................................................ 47


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Figures table:

1. Figure1: LASIK and PRK procedures .......................................................................... 8

2. Figure2: The foggy vision quality after LAISK. .......................................................... 9

3. Figure3: Pelli-Robson testing chart ........................................................................... 18

4. Figure 4: A sample of the results sheet ...................................................................... 19

5. Figure 5: Mars contrast Sensitivity (letters and numbers) Test Chart ......... 20

6. Figure 6: The Automated CSV-1000 Chart ............................................................... 21

7. Figure 7: CSV-1000E chart ....................................................................................... 23

8. Figure 8: CSV-1000RS chart ..................................................................................... 23

9. Figure 9: CSV-1000S chart ....................................................................................... 24

10. Figure 10: CSV-1000LanC chart .............................................................................. 24

11. Figure 11: the percentage of surgery duration between candidates. ....................... 26

12. Figure 12: the presence of any ocular pathology pre-surgical intervention. ............. 27

13. Figure 13: all the candidates were myopic. ............................................................... 27

14. Figure 14: the variability of results between the three tests (Pelli-Robson, CSV-1000,

and MARS), most in PRK, than post-LASIK and normal group. ............................. 29

15. Figure 15: scattergram shows the correlation between this study groups, using the

three CS tests .............................................................................................................. 31

16. Figure 16: shows the comparison of the mean contrast sensitivity for the three tests,

in the three sample groups. ........................................................................................ 32

17. Figure 17: variations of side effects in post-surgical patients. ................................. 33

18. Figure 18: percentage of people who was told about the vision reduction. .............. 34

19. Figure 19: number of people who done CSF tests before. ....................................... 34

20. Figure 20: satisfaction rate among patients. ............................................................. 35

21. Figure 21: changes occurred in vision post-surgery; most of them are good changes.

.................................................................................................................................... 35

22. Figure 22: none of the patients back to wearing conventional correction, except for

two wearing cosmetic CL. ......................................................................................... 36


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Abstract:

Introduction:

The ability to distinguish the different contrast level is a very important function of the visual system that indicates

a healthy visual system. Furthermore, Contrast sensitivity plays a very important role in everyday tasks such as

reading and driving car at night time. However, patients after LASIK surgery, which it supposed to make the vision

better, complain of reduce vision quality even after the healing period. Therefore, this research aims to evaluate the

quality of vision after the surgery by measuring contrast sensitivity level in comparison with visual acuity.

Knowing that the activity of daily vision scale (ADVS) Show that VA of 6/12 is equivalent to CS of 60 or less.

Purpose:

To determine whether the contrast sensitivity reduces after the refractive surgeries in comparison to the VA.

Methods:

Study design: a prospective study.

Participants: 100 adult patients of post PRK &LASIK candidates, from the ophthalmology and optometry clinic, of

an age of 18 and above due to the circumstances of the surgery, in duration of 3 months. Thecomparisons will be

between the patient’s values and information before the surgery and after it; if no retro information was

available the comparison will be to the normal values. A questionnaire will be given to see the reflection of the

patients. The contrast sensitivity was analysed with 3 types of charts were designed for that cause. They are

MARS letter contrast sensitivity chart, PELLI-ROBSON chart, and CSV-1000 with a viewer.

Results:

There is no significance change was found in the contrast sensitivity functions , post LASIK( P < 0.0001), unlike

the first hypothesis there was normal people having worse contrast sensitivity scores than the post-LASIK

candidates due to the statistical analysis, and the clinical results, however, PRK candidates had a lower contrast

sensitivity outcomes (P = 0.0004).

Conclusion:

LASIK refractive surgery had a little if any significance on the CSF, unlike the other type, PRK which had an

influential decreasing effect on the CSF, and that was concluded with the utilization of various tests, although one

test has proven its affectivity and reliability in differentiating the results between the candidate’s groups.

Setting:

Department of optometry, Applied Medical Science, King Saud University, Riyadh, KSA.


8

Chapter one:

Introduction


9

Chapter one: introduction and literature review.

1.1 Introduction

In the era of technology all the preceding problems aimed to overcome, the science is developing and likewise the

medical field. One of the most accountable organs is the eye, we account on our sight in dailylifeandhaving a

pleasant sight is essential. Therefore, the scientists started long time ago to offer alternatives one can avail of to

overcome sight problems.

One of the major interventions inophthalmology is refractive surgeries, which is a surgical procedure to correct

refractive errors such as, hyperopia, myopiaand astigmatism. Thisoperation provides the patient with a 20/20 vision

without the need fora correction such as glasses and contact lenses.

Figure1: LASIK and PRK procedures. (The dissection is done on the cornea)

1. 1 Laser in situ Keratomileusis (LASIK) is one of the utmost popular refractive surgery done currently all

over the world, is a surgical procedure to correct myopia by corneal stroma deduction. It embracing the use

of a microkeratome to create a lamellar dissection of the cornea creating a flap with intact corneal

epithelium. After the flap lifting, the underlying midstroma is reshaped with an Excimer Laser and the flap

is returned to its original position.(Year introduced: 2000)

1. 2 Photorefractive Keratectomy (PRK) it is a refractive surgery type, also to correct the refractive errors

in myopic, hyperopic and astigmatic patients, it is the introductory step in vision correction field, it differ

than LASIK in the procedural technique, it’s basically removing a portion of the anterior corneal epithelial

by Excimer laser, to produce a new radius of curvature.


10

However, one of many people who done this surgery complain of reduction on the quality of the vision. Therefore,

this research project aims toinvestigate if whether indeed, LASIK reduces the quality of vision? This will be

evaluated by measuring a related visual function which is contrast sensitivity.

1. 3Contrast sensitivity (CS) is defined as the ability to distinguish details at low contrast stages. CS overt

visual analyser ability to perceive differences in brightness between adjacent fields. Visual system’s ability

to realize the difference between objects and background at the level of finest details can be expressed as

the maximum level of contrast sensitivity. Used for decades, contrast sensitivity testing was commonly

used in experiments and clinical trials. Use of it as routine examination had relatively limited application.

Lately it has been reconsidered the importance of contrast sensitivity in assessing visual performance. Its

usefulness as a method for examining visual function was demonstrated in situations where impaired visual

function is not expressed by changes in usual indicators: visual acuity or visual field, so simply itsThe

ability to detect sharp boundaries (stimuli) and to detect slight changes in luminance at regions without

distinct contours .(VLAD RUSU,AMT, v. II, no. 3, 2014).

Patients with decreased Contrast Sensitivity frequently report decreases in the sharpness of their vision. Patients

may describe this as a “foggy” blur vision as seen in (figure 2). Visual acuity measurements may not be the reason

for the patient’s complaints. Contrast sensitivity testing can explain this reduction in vision better than visual acuity

screening. The real world is made of delicate variations in contrast, not the constant contrast of black on white as in

the visual acuity chart. Furthermore, a number of studies have proposed that impaired contrast sensitivity

contributes with increased crash risk in driving.

Figure2: The foggy vision quality after LAISK.


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1.2 Literature review

It was hard to find a lot of studies and articles about reduction of contrast sensitivity as a side effect of LAISK

surgery. The searching process was done on PubMed website in addition to other medical and researching journals.

The literature found was a plenty of researches about the effectiveness of LASIK, satisfaction and dissatisfaction

patients about LASIK results, the reliability of the utilized tests. Asummary of the literature found in table below.

Table 1: literature review in detailes.

Author and

year

Contrast

sensitivity

test

Type of

refractive

surgery

Results

Gary

Heiting, OD

Pelli-

robson.

-

Even if you have 20/20 visual acuity, you can have eye or health

conditions that may diminish your contrast sensitivity and make

you feel that you are not seeing well.

MaijaMänty

järvi, MD,

Tarja

Laitinen,

MD

Pelli-

Robson

contrast

sensitivity

test.

-

The Pelli-Robson contrast sensitivity test is a quick and reliable

method in a clinical setting. Normal values of the test can be of

help in evaluating cataract patients or patients having refractive

surgery.

Melki SA

Azar DT

2001

-

LASIK

(LASIK) is a rapidly evolving ophthalmic surgical procedure.

Refractive complications include unexpected refractive

outcomes, irregular astigmatism, decentration, visual aberrations,

and loss of vision with decreased CS.

Sridhar MS,

Rao SK

Vajpayee

RB

2002

-

LASIK

Laser-in-situ-keratomileusis (LASIK) has become a popular

technique of refractive surgery because of lower postoperative

discomfort, early visual rehabilitation and decreased

postoperative haze. The refractive complications include under

correction, regression in CS, irregular astigmatism, decentration

and visual aberrations.

http://www.allaboutvision.com/masthead-gary-heiting.htm


http://www.sciencedirect.com/science/article/pii/S0886335000005629





12

Jay

McLaren

,William M

Bourne ,Leo

J

Maguire201

5

-

LASIK

High-order wavefront aberrations increased and uncorrected

visual acuity improved immediately after surgery but these

variables did not change further to five years. There were no

differences in any variables between treatments.

A sustained reduction in keratocyte density does not affect vision

or optical properties of the cornea through 5 years after LASIK.

Charles qian

yu, Edward

E

Manche201

5

- LASIK

Higher-order aberrations were overall not increased at day 1 but

increased significantly by year 1. Objective aberrometric

refractions at postoperative day 1 can be useful in prediction of

long-term refractive outcomes.

There is a small myopic shift and an increase in higher-order

aberrations when comparing wavefront aberrometry results at

postoperative day 1 with those at postoperative 1 year.

Mahfouth A

Bamashmus

,Khammash

Hubaish,Mo

hammed

Alawad2015

- LASIK

Many myopic patients may have night time driving difficulties or

glare prior to surgery; thus, such symptoms postoperatively may

have less effect on satisfaction than surgeons might presume.

However, difficulties with nighttime driving can be a significant

problem for a minority of patients and should not be understated

during the informed consent procedure. The variation in

subjective assessment of functional and satisfaction parameters,

ophthalmologists, should look for other variables in addition to

the UCVA and residual refractive error, as the benchmarks for

assessing the outcome of refractive surgery.

J Donald , J

Li, M

Sarossy, A

Weymouth2

014

- -

Contrast sensitivity testing is an important part of visual

assessment and can identify visual deficits that go undetected by

measuring visual acuity (VA) alone. Despite this, contrast

sensitivity testing is rarely performed clinically due to the

expensive processes required and limited test availability, with

few spatial frequencies used. Further, gratings can be difficult for


13

subjects to learn and results are often not standardized.

Deirdre

Townley,

Caitriona

Kirwan,

Michael

O’Keefe.

2012

Pelli-

robson.

CSV

1000.

LASIK

One year postoperatively, there was no difference in CS between

both treatment groups using the Pelli-Robson and CSV-1000E

tests. CS was reduced postoperatively in the LASIK group at the

lower spatial frequencies under photopic conditions. No

postoperative change was detected in CS following LASIK or

LASEK using the Pelli-Robson test.

Roanne E

Flom,

Bradley E

Dougherty,

Mark A

Ballimore.

2005

Mars. -

Mars Letter Contrast Sensitivity Test shows excellent agreement

with the Pelli-Robson test and has similar repeatability. There are

subtle differences in the actual contrast levels on different forms

of the Mars test, and adjusting for these differences leads to

superior repeatability of the Mars test. Thus, the Mars test may

be a useful alternative to the Pelli-Robson test offering several

advantages.

Fatemeh

Heidary,

Roghayeh

Heidary,

Reza

Gharebaghi

2014

Pelli-

robson. -

This contrast sensitivity test has been used to examine vision in

different clinical circumstances. Moreover, as contrast sensitivity

is affected by several ocular states, its measurement has been

considered practically for monitoring and assessment of a wide

range of visual functions, predicting vision related abilities,

diagnosing several ophthalmic conditions, and evaluating many

ocular disorders including glaucoma, cataracts, diabetic

retinopathy, optic neuritis and age-related degeneration.


14

It was hard to find a lot of studies and articles about this topic, due to many factors, such as the lack of the

information, the newness of the procedures, and the tests recreations. The searching process was done on PubMed

website and other medical and researching journals. The outcome was a plenty of researches about the

effectiveness of LASIK (laser in situ Keratomileusis) and PRK, satisfaction and dissatisfaction patients about

LASIK results, the reliability of the utilized tests, moreover to comparing.

Its known internationally that LASIK procedures are the most utilized technique to correct the refractive errors,

many studies was done on their effect on incrementing the Visual Acuity and the percentage of patient satisfaction

after the surgery was at maximum levels.

A review by Sridhar MS shows that Laser-in-situ-keratomileusis (LASIK) has become a popular technique of

refractive surgery because of lower postoperative inconvenience, early visual reformation and detracted hereafter

operation haze. Approached to photorefractive keratectomy (PRK), LASIK includes an additional procedure of

creating a corneal flap. This might generates an elaborations related to the flap, ligature and underlying stromal

bed. Compared to PRK, there is less inflammation and faster recovery after LASIK, but there is an extended period

of sensory denervation leading to the elaboration of dry eyes. The refractive complications include undercorrection,

retraction, patchy astigmatism, decentration and optical aberrations. Genuine and impartial reporting is crucial to

understand the aetiology and redefine the management.

Another study about the amount of resentment patients agrees with the previous review, it

reviewed complications associated with the management options for dissatisfied patients seeking a consultation

after refractive surgery performing.

The result was a spectrum of complications associated with refractive surgery may result in patient displeasure.

Compatible patient selection, preservation strategies, and spontaneous diagnosis and medical or operative

intervention may be beneficial in managing complications and improving patient satisfaction.

Furthermore, a study by Melki SAwas done in Massachusetts Eye & Ear Infirmary, Boston, MA 02114, USA, and

states that Laser in situ keratomileusis (LASIK) is a rapidly evolving ophthalmic surgical procedure. Several

refractive and anatomic ramifications have been specified. Anatomic complications include corneal flap anomalies,

epithelial ingrowth, and corneal ectasia. Refractive complications include unforseen visual aberrations, irregular

astigmatism, refractive outcomes, decentration, and vision doom, withContrast Sensitivity diminution. Contagious

keratitis, curt eyes, and prevalent lamellar keratitis may also occur following LASIK. By examining the

aetiology, handling, and banning of these ramifications, the refractive surgeon may be able to ameliorate visual

http://www.ncbi.nlm.nih.gov/pubmed/?term=Sridhar%20MS%5BAuthor%5D&cauthor=true&cauthor_uid=12532491


15

outcomes and prevent vision-menacing issues. Recording outcomes and mishaps of LASIK surgery will help refine

our approach to the management of emerging complications. This means that there are complications and side

effects of this particular surgery, and neglected side effect of the operation is the Contrast Sensitivity.

Another related study by Deirdre Townley, determines the effect of conventional laser in situ keratomileusis

(LASIK) and laser epithelial keratomileusis (LASEK) for myopia on contrast sensitivity (CS) using the Pelli-

Robson and Vector Vision CSV-1000E CS tests. Deirdrededuced that CS was diminished postoperatively in the

LASIK group at the lower spatial frequencies sunder photopic conditions, which indeed agrees with Charles

Qianyu study, who had a similar results, Charles Qian yustated that Higher-order aberrations were overall not

increased at day one but increased significantly by year one.

Another study done by Gary Heiting, an optometry doctor says that the people who have low contrast sensitivity

may have problems at night driving, even a difficulty seeing pedestrians walking alongside poorly lit streets. They

might notice that their eyes tire more easily while reading or watching television. Patients who have LASIK may

be able to see 20/20 after the surgery but complains from decreased night vision. The surgery could cause a loss of

contrast sensitivity. Conversely, after LASIK, some patients achieve better contrast sensitivity and night vision

compared with their vision with glasses or contact lenses before the surgery.

For all these studies this research paper aimed to approve these results here in Saudi Arabia by examining the

contrast sensitivity function among post LASIK patients by using the most decisive tests. As well, there was a

plenty of researches about the available tests reliability and their capability to inspect an accurate Contrast

Sensitivity values. One of these studies is study by J Donald who found that Contrast sensitivity testing is an

important part of visual assessment and can identify visual deficits that go undetected by measuring visual acuity

(VA) alone. Despite this, contrast sensitivity testing is rarely performed clinically due to the expensive processes

required and limited test obtainability, with slight spatial frequencies utilized. Moreover, gratings can be risque for

candidates to learn and results are often not standardized. Pelli-robson, Mars, and CSV-1000 were used in this

study upon many tests due to their validation and reliable results.

Maija Mäntyjärvi assures this by his study about Pelli-robson who stated, The Pelli-Robson contrast sensitivity

test is a quick and reliable method in a practice tuning. Average rates of the test can be of aid in evaluating cataract

patients or patients having refractive surgery.




16

As well as,Roanne E Flomwho studied Mars CS test and deduced that, Mars Letter Contrast Sensitivity Test

demonstrates excellent agreement with the Pelli-Robson test and has similar recurrence. There are tender variations

in the current contrast levels on different forms of the Mars test, and adapting for these differences progress to

superior repeatability of the Mars test. Thus, the Mars test may be a beneficial alternative to the Pelli-Robson test

offering several advantages. After guidance of all the previous studies, this research was launched.

Chapter two

Methodology


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Chapter two: the Methodology.

2.1Methods

The aimwas to examine a sample of 100 patients or more. The adopted method in this research was a prospective

and retrospective cross-sectional study. This has been done to compare the contrast sensitivity function in normal

andpatient of LASIK surgery. Furthermore, these results were compared with the visual acuity after the surgery. If

the patient’sfilesdid not include contrast sensitivity results, we will do it by three different tests; Pelli-Robson test,

Mars Chart and CSV 1000.All of these tests are used worldwide because of their high level of accuracy. All of the

tests have been done after standard visual acuity testing and before pupil’sdilation.

1.1 Statistical analysis was done using graphpad prisms to compare between results of contrast sensitivity post

LASIK &PRK with the Visual Acuity values, and the normal people. Coefficient correlation and linear

regression was used to examine the difference between the two groups. Using the analysis of variance

(ANOVA) the p-value was calculated and P=0.05 or lesswill consider statistically significant.

1.2 A questionnaire was given to the patients, to evaluate their vision quality.

2.2 Materials:

As previously mentioned, candidates for this study were students of king Saud University, divided into two groups:

normal group which used as control group (n=20), and patients who previously done refractive surgery (n=31)),

those also were divided into two sub-groups , post-LASIK (n=25) and post PRK (n=6) . Each one was examined

for the contrast sensitivity function by the three different tests (table 2), after going under visual acuity examination

earlier using the Auto-Refractometer, and conventional VA via Snellen chart. Then they were asked to fill the

questionnaire and sign the participation consent form.


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Table 2 shows the advantages and disadvantages of each test used in the research:

Test Advantages: Disadvantages:

Pelli-Robson

1. Widely used test world and it uses the ability

to detect letters that are gradually less

contrasted with the white background.

2. Good repeatability.

3. Is easily understood by patients and no

special examination conditions required.

4. Is carried out quickly (up to 8 min.)

1. they are not of equal legibility, the legibility

of these letters to differ by less than

20%.

2. Explore the low frequency of contras.

MARS

1. Hand-held, and designed for convenient

near-vision testing.

2. Testing is rapid generally under a minute

per eye for testing and scoring.

3. Smaller size, enhanced stability, and use

facilitation.

1. Not ideal for low vision patients.

2. Smaller angular substance of the letters

when compared with pelli-test. (Optometry,

Mark Rosenfield)

CSV-1000

1. Auto-calibration.

2. Ease of use.

3. Standardized measurement of contrast

sensitivity.

1. Needs effort to move.

2. Not available in all medical institutions.


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2.3 Contrast sensitivity testing:

A. PELLI-ROBSON contrast sensitivity chart:

It was designed by DG Pelli, JG Robson and A J Wilkins, in the aim to put a realistic assessment of how well the

patient sees large faint objects.

It is the most widely used test world and it uses the ability to detect letters that are gradually less contrasted with

the white background.

It’s like the standard Snellen chart in importance, it consists of horizontal lines of capital litters, and the contrast of

the letters is decreasing downwards with each line. It is different from common visual acuity testing in a regular

eye; it measures the ability to recognize smaller and smaller letters on a standard eye chart.

For many reasons and in different situations Contrast sensitivity is a very important measure of visual function,

especially in situations of fog or glare, and low light. An example of an activity that requires good contrast

sensitivity for safety is driving at night.People, who have 20/20 visual acuity, can have eye or health conditions

that may diminish the contrast sensitivity and make them feel that they are not seeing well.

It was applied at a distance of 40 inches (1m) and an illumination of 85 cd/m².The lowest contrast at which 2 or 3

of the letters in a group can be read determines a log contrast sensitivity result. An outcome of 2.0 indicates

average contrast sensitivity (100 percent), whereas a score below 1.5 submits sensitivity impairment

Figure 3: Pelli-Robson testing chart.

http://www.allaboutvision.com/eye-test/


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Figure 4: A sample of the results sheet.

B. Mars Contrast Sensitivity Tests...

It is the choice of eye care professionals, occupational testers, and clinical researchers around the globe,

because of the accurate results and rapidly-administered contrast sensitivity measurements.

Unlike other contrast tests that assess visual acuity using low contrast marks, the Mars tests are proper contrast

sensitivity tests that assess the lowest contrasts your patients enable to observe, instead than the smallest

letters they can sympathize at some low, arbitrarily chosen contrast. With the Mars tests, it is the contrast, and

not the letter (or numeral) size, which minimizes from the outset to the end of the chart.

http://www.marsperceptrix.com/mars-contrast-sensitivity-tests


21

Figure 5: Mars contrast Sensitivity (letters and numbers) Test Chart .(A)the letter type &(B)the

numerical type.

It is commonly carried out to observe functional effects of disease progression, Assess contrast sensitivity

pre and after an intervention, Occupational testing and licensing, identify functional losses in low contrast

perception and Clinical trials for cataract, refractive surgery and ophthalmic pharmacologic agents.

It asses the contrast sensitivity at near distant, Comes with three charts, for the left eye, right eye and

binocular testing, or for repeated testing.

Due to of many advantages of Mars test, it was chose to be one of the tests in this study. It is a Hand-held, and

designed for convenient near-vision testing. Each chart is printed with 48 different contrast scales, descending

gradually in 0.04 log unit paces the finest steps available in any printed contrast test. Furthermore, Testing is

rapid generally under a minute per eye for testing and scoring. Finally, it is Available in both letter

and numeral versions.

It is done by placing the patient around 50 cm (20 inches), apart off the chart. And the near viewing distancemay

range from the standard distance of 40 cm (15.75 inches) to 59 cm (23 inches). Patients should wear their habitual

distance correction, or their near correction, with add of +2.00 D and covering the untested eye. The test should be

performed with the eyes un-dilated.


22

C. CSV-1000:

It is the most recognized world-wide leader for standardized contrast sensitivity.

This auto-calibration circuitry provides for standard and consistent test conditions without a hassle. It’s

automatically controls the test lighting to a level of 85 cd/m2, which is the illumination level admonished for vision

testing by the National Academy of Sciences and adopted by the FDA as the required testing light level for clinical

trials.

Ease of use is one reason why the CSV-1000 is used in eye clinics in more than 60 countries. All what is required

is to turn on the device and it is ready to evaluate patients using standardized and highly accurate tests.

A review of (Glenn Pomerance, MD Chattanooga, TN) says: I have a CSV-1000 in every examination lane. There

are no moving parts that can break, and I’ve been so satisfied with the technology that I wouldn’t hesitate to buy

(these) devices if I needed to replace one. However, that has been a moot point because the units have continued to

work reliably day after day for years.”

A B

Figure 6: (A) It usually comes on a stand with lights. (B) The Automated CSV-1000 Chart.


23

Further than 100 released papers have expounded the usefulness of the CSV-1000 for a variety of applications

including Measurement of the IOLs and refractive surgery technology.

It is been used as a clinical tool in more than 5,000 eye care practices around the world, CSV-1000 also it is

routinely used for research and to evaluate visual performance.

It has been selected for use in numerous multi-centre trials in the United States and around the world for the

standardized measurement of contrast sensitivity, ETDRS acuity, low contrast severity and glare sensitivity. These

surveys implicate those for the estimation of LASIK surgery.

There are various contrast sensitivity tests that can be used with the CSV-1000: E, RS, S and SLanc.

Some of these tests are widely used in the world, because they provide a full contrast sensitivity curve, and some

are more often used because the capability of using them for the evaluation of the ocular diseases. Other types are

specially used for out-of-office screening, some of them serve the same purpose but with a change in the form of

the test.

CSV-1000E:

The CSV-1000E chart test face is the most globally used contrast sensitivity test. At advised test distance of 8 ft

(2.5 meters), the test supplies four (4) rows of sine-wave gratings, these scales evaluate the spatial frequencies of

18, 12, 6 and 3 cycles/degree (CPD). It alsoequips a wholecurve of contrast sensitivity, in which is very helpful in

the screening of ocular disease (in particular,cataracts,glaucoma, macular degeneration and diabetes), refractive

operationandcontact lenses. In cataract appraisal/instrumentation, a functional acuity outcome can be gained

directly from the test scoring sheet.

For those interested in using the CSV-1000E in studies, the test face is available in two versions. The Contrast

Sensitivity CSV-1000E Chart 1 supplies randomized locations for the grating targets.


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Figure 7: CSV-1000E chart. (Different shades of contrast filters)

CSV-1000RS:

The CSV-1000RS test face is used widely for screening patients who have done refractive surgery. The test

precedes ETDRS LogMAR acuity from 20/100 to 20/10 and one row of spatial frequency at 12 cycles/degree.

The patient can be readily evaluated in the examination seat for ETDRS acuity and contrast sensitivity. If a contrast

sensitivity deficiencywasdetected, reevaluating the patient with all four spatial frequencies using the CSV-1000E is

admonished.

Figure 8: CSV-1000RS chart. (Descending acuity charts are involved in addition to the filters)


25

CSV-1000S:

The CSV-1000S test face is widely used for in or out-of-office and for cataract screenings. This test displays a

standard visual acuity from 20/15 to 20/200, two rows of spatial frequencies (6 and 12 cycles/degree) and a real-

world driver’s scene.

Figure 9: CSV-1000S chart. (Different than the previous two by adding sections to an advances

screening)

CSV-1000SLanC

The CSV-l000SLanC test face equips the same tests as the standard CSV-1000S, except that the acuity test is

presented in Landolt C format. This test is very beneficial when screening patients who cannot read the English

alphabet.

Figure 10: CSV-1000LanC chart. (Same as the previous one test but with landolt C format)


26

Chapter three

Results


27

chapter three:

3.1 Result

3.1.1 Summary of the sample from the questioner: Q1, 3 and 4.

While the results was recorded by the examiner, all the candidates (except for the control group) had to fill out a

questionnaire monitoring crucial subjective information about the surgery and its correlation to the CSF results,

most of the patients had done the surgery short time ago, which may contribute inversely and explain the good CSF

after adaptation as shown in graph 11.

No other ocular pathology was present, this also help in maintaining a good CSF after the surgery, graph 12.

Figure 11: shows a graph the percentage of surgery duration between candidates.

26%

35%

16%

23%

surgery done before

0-3 MON. 3-6 MON. 6 M - 1 Y 1-3 YEARS


28

Figure 12: shows the presence of any ocular pathology pre-surgical intervention.

Fourth question was to know if the,at the beginning of the study we wanted to know the relation between the type

of the refractive error and the results, and witherrefractive error could have an effective change on the vision

quality, or the kind of the surgery, but what discovered later that all the candidates were near sightedness (myopes)

Figure 13.

Figure 13: all the candidates were myopic.

0%

100%

presence of any ocular condition

yes

no

100%

0%

refractive error present before the surgey

myopic

hyperopic


29

3.1.2 Anova

There is no significance change was found in the contrast sensitivity functions , post LASIK( P < 0.0001), unlike

the first hypothesis there was normal people having worse contrast sensitivity scores than the post-LASIK

candidates due to the statistical analysis, and the clinical results, however, PRK candidates had a lower contrast

sensitivity outcomes (P = 0.0004).

Table 3 shows the statistical analysis of post-LASIK results.

Table Analysed LASIK

ANOVA table SS DF MS F (DFn, DFd) P value

Treatment (between CS tests) 1.431 2 0.7157 F (1.608, 36.98) = 60.05 P < 0.0001

Individual (between subjects) 0.3048 23 0.01325 F (23, 46) = 1.112 P = 0.3695

Residual (random) 0.5483 46 0.01192

Total 2.285 71

Number of treatments (columns) 3

Number of subjects (rows) 24

Table 4 shows statistical analysis of post-PRK results.

Table Analyzed PRK

ANOVA table

SS DF MS F (DFn, DFd) P value

Treatment (between CS tests) 1.556 2 0.7780 F (1.061, 5.303) = 18.87 P = 0.0062

Individual (between Subjects) 0.1590 5 0.03180 F (5, 10) = 0.7712 P = 0.5915

Residual (random) 0.4123 10 0.04123

Total 2.127 17



Table 5 shows statistical analysis of normal candidates (control group).

Table Analyzed Normal


Treatment (between CS test) 1.024 2 0.5122 F (1.243, 23.62) = 53.81 P < 0.0001

Individual (between Subjects) 0.3108 19 0.01636 F (19, 38) = 1.719 P = 0.0765

Residual (random) 0.3617 38 0.009518

Total 1.697 59




30

However, other than the statistical base, the three tests had a variations in the outcomes as shown in figure 13, the

first group was post-LASIK group, which dissected into three section, Pelli-Robson which had a CSF of 1.95 in

most of the candidates, the minimal degree was obtained was 1.65 OU, along with the normal candidates (control

group), and post-PRK pts. The same was obtained. While in MARS test there were a little higher variation in

scores varied between 1.4 as a minimum in post-PRK pt. and 1.7 in normal healthy candidates. Last but not least

the ultimate distinction was noticed in CSV-1000 where we got a result as low as 0.61 in post-PRK patients and as

high as 1.84 in normal candidates (control group).

N o r m a l

S u b j e c t s

Lo

g c

on

tr

as

t s

en

sit

iv

it

y

0 5 1 0 1 5 2 0 2 5

0 . 0

0 . 5

1 . 0

1 . 5

2 . 0

2 . 5

P - R

M A R S

C S V

L A S I K

S u b j e c t s

Lo

g c

on

tr

as

t s

en

sit

iv

it

y

0 1 0 2 0 3 0

0 . 0

0 . 5

1 . 0

1 . 5

2 . 0

2 . 5

P - R

M A R S

C S V

P R K

S u b j e c t s

Lo

g c

on

tr

as

t s

en

sit

iv

it

y

0 2 4 6 8

0 . 0

0 . 5

1 . 0

1 . 5

2 . 0

2 . 5

P - R

M A R S

C S V

Figure 14: scattergram shows the variability of results between the three tests (Pelli-Robson, CSV-1000, and

MARS), most in PRK, than post-LASIK and normal group.


31

Table 6: shows the correlation between the two surgeries, utilizing CSV-1000 test.

Table Analyzed CSV-1000 WITH TWO

SURGERY

Column B PRK

vs. vs.

Column A LASIK

Paired t test

P value 0.0331

P value summary *

Significantly different? (P < 0.05) Yes

One- or two-tailed P value? Two-tailed

t, df t=2.917 df=5

Number of pairs 6

Table 7: shows the correlation between the two surgeries using Pelli-Robson.

Table Analyzed P-R two surgery

Column B PRK

vs. vs.

Column A LASIK

Paired t test

P value 0.6952

P value summary ns

Significantly different? (P < 0.05) No


t, df t=0.4152 df=5

Number of pairs 6


32

Table 8: shows the correlation between the two surgeries using MARS test.

Table Analysed MARS two surgery

Column B PRK

vs. vs.

Column A LASIK

Paired t test

P value 0.0199

P value summary *

Significantly different? (P < 0.05) Yes


t, df t=3.371 df=5

Number of pairs 6

0 2 4 6 8

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

C S V -1 0 0 0

S u b je c ts

Lo

g c

on

tr

as

t s

en

sit

ivit

y L A S IK

P R K

N o rm a l

M A R S

S u b je c ts

Lo

g c

on

tr

as

t s

en

sit

ivit

y

0 2 4 6 8

1 .4

1 .5

1 .6

1 .7

1 .8

1 .9

L A S IK

P R K

N o rm a l

P -R

S u b je c ts

Lo

g c

on

tr

as

t s

en

sit

ivit

y

0 2 4 6 8

1 .4

1 .6

1 .8

2 .0

2 .2

2 .4

L A S IK

P R K

N o rm a l

Figure 15: a scattergram shows the correlation between this study groups, using the three CS tests.


33

Table 9: shows the statistical P value between all the groups.

C o m p a r e s e io n o f th e m e a n c o n tr a s t s e n s it iv ity

fo r th e th re e te s t in th e th re e s a m p le g ro u p s .

C o n tra s t S e n s it iv ity T e s t

Lo

g c

on

tr

as

t s

en

sit

ivit

y

0 4

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

L A S IK

P R K

N O R m al

P -R M a rs C S V 1 0 0 0

Figure 16: shows the comparison of the mean contrast sensitivity for the three tests, in the three sample groups.

Quality of vision from the questionnaire: Q 2, 5,6,7,8,9,10.

Post-surgery complications was the most annoying symptoms in the whole process, said one of the patients, which

made us concern in what exactly the patient complaint, because not everyone is a suitable candidate for the

surgery. A large aspect of them reported having dry eye syndrome; the cause could be either a decrease in the tear

production, or another systemic cause, although most of doctors positively assure the patients that it’s only a

temporary condition, some of them still complaining so, they are using hydrating drops prescribed previously by

their doctor.

Secondly, the most frequent complaint was poor night vision, and halos, this problem could be permanent or

temporary, most of the cases experienced this side effect because of the corneal swelling, post-surgical, figure 17.


Treatment (between groups) 0.08482 2 0.04241 F (1.005, 2.011) = 2.388 P = 0.2620

Individual (between contrast sensitivity tests) 0.2996 2 0.1498 F (2, 4) = 8.435 P = 0.0367


34

Figure 17: shows the variations of side effects in post-surgical patients.

As what will be mentioned in the study limitation, few candidates done the CSF evaluation, some of them were

confused about the tests, and mentioned never seeing them before, which made it hard to take an idea on what was

their CSF pre surgery,as shown in figure 18.

A crucial issue should be discussed, is the patient – doctor relationship, it should be built on honesty and

confidentiality, but that wasn’t the exactly scenario in this study, cause a large amount of people reported, that even

their doctor who suggested the surgery for them, didn’t let them have the acknowledge that their vision may be

diminution or they may develop astigmatism, which is un proper, figure 19.

22%

34%

17%

27%

complications post surgery

poor V. at night

dry eye

glare or haloes

more than one


35

Figure 18: shows the number of people who done CSF tests before.

Figure19: shows the percentage of people who was told about the vision reduction.

All in all, most of the patients, reported the gratification about their quality of vision post-surgery, andhaving a

minimal unfavourable visual changes, despite the fact that none of them returned back to wearing the old

conventional, heavy glasses or contact lenses, figure 20, 21 and 22.

0%

32%

68%

0%

have you done CS test before

have you done CS test before the surgery

yes (pre or post)

no

I don’t known

yes39%

No61%

patients aknowledge of post surgery vision reduction


36

Figure 20: shows the satisfaction rate among patients.

Figure 21: shows the changes occurred in vision post-surgery, most of them are good changes.

2%

4%5%

7%

9%

11%

13%15%

16%

18%

satisfaction scale rate

1 2 3 4 5 6 7 8 9 10

0%

48%

13%

39%

changes noticed in vision with time

yes, good

yes, bad

No


37

Figure 22: shows that no one of the patients back to wearing conventional correction, except for two wearing cosmetic

CL.

3.2 Discussion:

According to the literature review, many studies suggested that there is a reduction in the contrast sensitivity due to

the laser procedure, in this clinical experiment many variables was noticed that hasn’t been mentioned before in

any clinical trial or study, post-LASIK candidates were having a good contrast sensitivity in contrast to the other

group, maybe this because of the different surgical procedure, for the admonition purpose, LASIK procedure don’t

include any tissue extraction, it only make a flap which will be returned after laser exposure, surprisingly, in

comparison to the normal candidates (control group) some of the first mentioned had a better contrast sensitivity.

Post-PRK patients had the most contrast sensitivity function diminution, likewise earlier suggested because of the

surgical technique, unlike LASIK, PRK mainly depends on removing the whole anterior corneal epithelium,

making the patient more prone to the reduction of the quality post operation, which denies our supposition that the

LASIK have a dramatically reduction effect on the CSF. Coming to the gold standard in measuring the CSF many

studies suggested the previously mentioned tests, by visiting the local clinics it was discovered that the only test is

using is Pelli-Robson, by candidacy of many eye specialists, it has the most famous reputation, yet when clinically

experimented it gave almost a unified results for all the cases, despite the fact that all candidates have different

corneal curvature, and there must be a change in the quality of the CSF, thus this test reliability level reduced.

6%

94%

back to refractive error correction

yes

no


38

in the other hand, the CSV-1000 was the least test used in the studies, even though it’s not available in most of the

eye clinics, when utilized in this clinical study it have been found that it gives an accurate results in contrast with

other tests, as shown in figure 13, so its suggested to be replaced by Pelli-Robson in clinics, due to its high

reliability and variability. When analysing questionnaire data collected from the patients, important aspects was

noticed, one of them was the unawareness of the surgery effects, wither the advantages or disadvantages, according

to the questionnaire more than half of the patients denied that their doctor educated them about the surgery prior to

it, figure 15.

3.3 study limitation:

This study had various limitations; first one was the inability to do pre-operation evaluation of the contrast

sensitivity to compare it to the post-surgery results, because most of them had already done the surgery before

coming to the clinic to participate in the study. In addition it was hard to handle the study in a hospital due to lack

of the appropriate equipment’s, the wanted equipment’s were only found in the university clinics with no ability to

take them to the hospitals location. Due to the previously mentioned problem it was likewise impossible to reach

candidates previous files to check wither they have done any CSF tests before the surgery or not, adding the lack

of reaching all colleges in the university, in order to complete the wanted number of patients which led to only

reaching half of the wanted quantity.


39

Chapter four

Conclusion


40

4.1 Conclusion:

Based on this study, over 70% of the candidates were satisfied of the post-surgery results and the offered vision

either quantitative by correcting their refractive error or quantitative by the quality of the vision, LASIK turned to

have a minimal diminution effect on the CSF, while PRK had the worst sequels, that makes us confused if the PRK

really should be discontinued in the clinics due to its effects on the CSF. After clinically practicing the three tests

on the given population, CSV-1000 have proven its efficacy in obtaining an accurate measurement of the required

CSF, unlike Pelli-Robson test which was the standardized contrast sensitivity screener. Nevertheless, little pieces

are still missing in this study due to the inability to obtain a greater quantity, unreachable post CSF evaluations,

and the lack of reaching other trials,further inspection still should be done.


41

References


42

References:

1-A Bamashmus, M., Hubaish, K., Alawad, M., & Alakhlee, H. (2015, January 1). Functional Outcome and Patient

Satisfaction after Laser In Situ Keratomileusis for Correction of Myopia and Myopic Astigmatism. Retrieved May

5, 2015.

2- CSV-1000 - Standardized Vision Testing Instrument. (n.d.). Retrieved April 26, 2015, from

3- Contrast Sensitivity Testing. (2015, January 1). Retrieved May 2, 2015.

4- Cobo-Soriano R, Calvo MA, Beltran J, Llovet FL & Baviera J (2005): Thin flap laser in situ keratomileusis:

analysis of contrast sensitivity, visual and refractive outcomes. J Cataract Refract Surg 31: 1357–1365.

5- Donald, J., Li, J., & Sarossy, M. (2014, September 1). Developing a clinically viable protocol for measuring and

analysing the human contrast sensitivity function on a standard computerised chart. Retrieved April 23, 2015.

6- Dougherty, B., Flom, R., & Bullimore, M. (2005, December 1). An evaluation of the Mars Letter Contrast

Sensitivity Test. Retrieved May 3, 2015.

7- Hadavand, M., Heidary, F., Heidary, R., & Gharebaghi, R. (2014, January 1). A modified middle eastern

contrast sensitivity chart. Retrieved April 20, 2015.

8- Mclaren, J. (2015, April 1). Changes in Keratocyte Density and Visual Function Five Years after Laser in situ

Keratomileusis: Femtosecond Laser vs Mechanical Microkeratome. Retrieved April 5, 2015.

9- NLM Controlled Vocabulary. (n.d.). Retrieved May 2, 2015.

10- Optometry: Science, Techniques and Clinical Management..

By Mark Rosenfield, Nicola Logan, Keith H. Edwards.

Rosenfield, M., & Logan, N. (n.d.). Optometry. Retrieved May 5, 2015.


43

11- N, Y., K, M., & T, S. (2004, November 1). Ocular higher-order aberrations and contrast sensitivity after

conventional laser in situ keratomileusis. Retrieved May 16, 2015.

12- Qian yu, C., & E Manche, E. (2015, March 1). Day 1 Wavefront Aberrometry for Prediction of Refractive

Outcomes at Year 1 in Myopic LASIK. Retrieved May 1, 2015.

13- Result Filters. (n.d.). Retrieved April 18, 2015.

14- RUSU, V., MIHAI, E., & STĂNILĂ, A. (2014, August 25). CONTRAST SENSITIVITY IN DIABETIC

RETINOPATHY. Retrieved May 11, 2015.

15- Townley, D., Kirwan, C., & O'Keefe, M. (2012, February 1). One year follow-up of contrast sensitivity

following conventional laser in situ keratomileusis and laser epithelial keratomileusis. Retrieved May 3, 2015.

16- The reliability of the pelli-robson contrast sensitivity chart. (n.d.). Retrieved May 1, 2015.

Index:

Questionnaire:

Name:………………………………… age:……………………………. Sex:……………………………….

1- When have you done the surgery:

A- Less than 3 months.

B- 3 – 6 months.

C- 6 – 1 year.

D- More than year.

2- Did your doctor tell you that the quality of vision may reduce :

A- Yes.

B- No.

3- Do you have any ocular disease :

A- Cataract.


44

B- Glaucoma.

C- Age related macular retinopathy.

D- Other.

………………………………………………………………………………………………………………………………………………

4- Before the surgery you was:

A- Myopic.

B- Hyperopic.

C- Have astigmatism.

5- Do you noticed any of those complications after the surgery:

A- Difficulty at night-time driving.

B- Dry eye.

C- Glare or haloes.

D- Other.

………………………………………………………………………………………………………………………………………………

6- On a scale of 10 what is the rate of post operation satisfaction:

Not satisfied (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) Satisfied

7- Are you back to wearing glasses (distance – near):

A- Yes (distance – near).

B- No.

.......................................................................................................................................................

8- Post-operative quality of vision :

A- Increased.

B- Decreased.

C- Remains the same.

9- Have you done the contrast sensitivity test pre or post operation :


45

A- Yes, (pre, or post operation).

B- No.

10- is there changes with time (good or bad) :

A- Yes Good.

B- Yes Bad.

C- No.


46

Consent of participation and agreement.

Does lasik reduces the quality of vision while enhancing the VA ?

We invite you to participate in this study, to approve or deny whether the Contrast Sensitivity

Function decreases after the LASIK surgery or not. We will evaluate the vision by many tests by

taking first the Visual acuity then the Contrast Sensitivity by 3 different tests, and comparing the

results to see the difference and weather it increasing or decreasing indeed.

The patients selection will be based on those who have previously done the surgery and if there is

any possibility, we will chick their file to see if there is a previous contrast sensitivity testing, and

compare the results.

If you decided to participate in this study, so the optometrist will evaluate the vital signs of the

vision, which is VA in addition to the contrast sensitivity, the tests will be based on evaluating the

patient vision quality, and the dissatisfaction he may have after the LASIK, in contrast to his status

before the surgery.

This may take up to 30 minutes; in addition there is a questioner you have to fill to evaluate his

acceptance and the comfort after the LASIK in aim to reach the maximum degree of comfort and

vision quality provided.


47

The information, results and complaints will remain confidential and no one have the access to it

unless on the patient request.

If you agree to participate in this study then you have accepted the conditions of it, and the

probability to discuss the results, in the current research, conferences and any other medical

institution, with the knowledge that your identity will remain confidential.

Your decision to accept the participation or not will not put you in any harms or a bad situation,

and if accepted to participate, you have the right to withdraw under any circumstance.

You have made the decision to accept or refuse the participation in this trial,

along with your signature you admit that you have read the participation

statement information, and decided to be a part from this study:

Name:

……………………………………………………………………………………………………………..

Signature:

…………………………………………………………………………………………………………….

Date of beginning:

……………………………………………………………………………………………………………

Date of ending:

……………………………………………………………………………………………………………

Researcher signature:

………………………………………………………………………………………………………….

Researcher Name:

Toka alminyawy .


48

Documents

Does refractive surgeries (PRK VS. LASIK) reduces the Contrast …fac.ksu.edu.sa/sites/default/files/2-does_refractive... · 2019-02-16 · refractive surgery Results Gary Heiting,