What do I see ? Questions and tests

June 17th 2010

Mary Bairstow

Low Vision Services Implementation Officer

About the presentation

• Low Vision and integrated working

• Anatomy and its relation to disease

• Just a couple of eye ‘conditions’

• Some interludes - ‘practice makes perfect”

• Review and questions

Why work together ?

• Whole child view

• Assessment of function to determine need

• Provide additional advice on ‘medical questions’

• Check on change / monitor risks

• Work on (re)habilitation skills

Defining Low Vision

“A low vision service is a rehabilitative or habilitative process which provides a range of services…… to make use of …eyesight…to achieve maximum potential.”

“This is not just a technical process”

Low Vision Report

Child Centred

1

28

7

6

3

4

5

1. The child 2. ‘Synpedagog’, low

vision teacher

3. Ophthalmologist

4. Optometrist

5. Psychologist

6. LV Counsellor

7. Rehabilitation Officer

8. SecretarySwedish ‘model’International Conference

on Low Vision 1990

9. Parents

Come into the clinic

“History and symptoms”

• Birth history

• Medical history/ genetics

• General health - tablets/medication

• Eye health

• Parents /child’s impression of sight

• Tasks want to do

Its all about detection !

• We see between 380-700 nm

• U-V and I-R are invisible but may have affects on the eye due to absorption

The structure of the eye

The retina• 90% of light passes through the vitreous

gel to the retina

Diagram from Rodieck, The first steps in seeing

www.mdsupport.org/images/retlayers.jpg

Cones or gnomes

• 120 Million rods

• 6.3 million cones

Rods

• Bleached by normal light

• Can pick up small amounts of light energy which is amplified

• Not good at detail

• Reduce around the fovea with age

Cones

• Most densely populated at the macular

• Identified by the ‘yellow’ pigmented area

• Pigments Lutein and zeaxanthin

• Neuronal links give good resolution

So the foundation for….

• Looking at Stargardt’s

Stargardt’s

What is it?

Condition caused by excessive lipofuscin

storage characterised by flecks at the

macula and vermilion coloured fundus.

Causes

Most patients it is inherited (autosomal

recessively). Mutations in a gene called ABCA4

are responsible for the majority (75-90%)

Clinical Picture

• Back of eye (fundus) may appear normal -

misdiagnosis non-organic ('hysterical') loss• Flecks appear as elongated shapes. • Retinal atrophy - shimmering beaten metal• Colour vision may become affected. • Peripheral vision rarely affected

New Examination techniques – OCT (Optical Coherence Tomography)

© BMJ Publishing Group Limited 2007.

New Treatments

• Gene Therapy• Adeno-associated virus to sneak the corrected gene into affected

cells• No new genes - simply introduce a new gene.

• Reasons for hope• Has been successfully treated in mice• Diagnosed in young people where therapy would be most

effective.• Advances in screening allow selection of suitable patients for

clinical trials.

Symptoms

• Loss of detail in reading

• Colour vision loss

• Loss of eye contact – social/ emotional issues

• Photophobia

Help available?

• Advise on eccentric viewing.

• Magnification for near and distance.

• Localised illumination.

• Filters for glare (+ protection).

• Monitor progression. Condition progresses and usually stabilises in 20's.

What is visual acuity

• Vision is seeing

• Acuity is a measure of degree

• Visual acuity is a measure of the smallest detail a person can just see

“Snellen” I presume

• Visual acuity often is referred to as “Snellen” acuity.

• Chart / letters named after 19th-century Dutch ophthalmologist Hermann Snellen (1834–1908) who created in 1862

• “Acuity” comes from the Latin “acuitas,” which means sharpness

• Sharpness = resolving limit = ‘just seeing’

Copy from Dr Kathryn Saunder’s website @ University Ulster

Limit of sight

• It is the gap we can just see

• Make the same sized angle at different distances

It’s all numbers to me

• The first line of type is a size that means this angle is formed at a distance of 60 metres

• The second at 36 metres, then 24, 18, 12, 9 and 6 metres. Extra lines may be at 5 and 4 metres.

Tents and igloos

• Chart held at ‘convenient distance’- UK this is usually 6 metres (USA use 10 feet as they have testing rooms this long )

• Over 6 metres tests infinity as far as can see

The results are expressed as a fraction

• ‘Standard vision’ means someone could walk back to 36 metres and still see the second line

• Someone stuck on the 2nd line at 6m has 6/36 vision

Uneven SpreadSnellen Progression

60

36

24

18

129

6 5

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

6 0 3 6 2 4 1 8 1 2 9 6 5

The solution

• Logarithms

LogMar charts

– Most lines have similar level of visual difficulty – Equal numbers of letters on each line rather

than one single letter on the Snellen chart Distance VA chart

– Improved child confidence– Use accurately at different distances– Each letter has a value, most lines of letters

are all of similar visual demand

Choosing tests

• Accuracy and repeatability

• Pre-school and not ‘reading’ – Cardiff , LH shapes and ‘crowded’ Kays

• Letter readers – LogMAR acuity

Understand norms

Visual Acuity Norms

(Cardiff acuity test)

age (mths) binoc VA monoc VA

12 - 17.9 6/48 - 6/12 6/48 - 6/15

18 - 23.9 6/24 - 6/7.5 6/30 - 6/7.5

24 - 29.9 6/15 - 6/7.5 6/19 - 6/7.5

30 - 36 6/12 - 6/6 6/12 - 6/6

Visual Acuity Norms

(crowded optotype test)

age (years) binoc VA monoc VA

2.5-<3.5 6/12 6/12

3.5-<5.0 6/9 6/12

5.0-<6.0 6/9 6/9

6.0+ 6/6 6/9

90% of ‘visually normal’ children will have acuity of this level or better. Only when vision is below this level for age can it be said that there is evidence to say they have a significant visual acuity deficit.

Dr Kathryn Saunder’s @ University Ulster

‘Size’ reserves

• Acuity reservesFluent reading 160 words per minute 3:1 acuity reserve

Spot or survival reading 40 words per minute 1:1 acuity reserve

Practice makes

Perfect

Visual pathway

• Various neuronal connections transmit out of the eye via one million ganglion cell axons

• Blind spot no receptors

Visual pathway

• Nerves leave and cross over at the chiasm

• Cross- wiring to link visual world .

• Left half of brain interested in right side of world

The pathway

Right sight loss

• Where in the pathway?

• How do you know ?

What’s this

• Where has this happened?

• What could be wrong?

And where is the problem?

• This one ?

• So why can’t she read?

Haemianopia

Haemianopia

• What is it

• Loss of peripheral (half of vision)

• In both eyes

• Due to loss of nerve fibres in visual field

Clinical Picture

• Left Lesion

• Left Occipital lobe

• Right Haemianopia

Clinical picture

• Childhood Stroke

• Intercranial haemorrhage (birth trauma/prematurity/ head injury)

• Development issues

• Tumour - pituitary

Symptoms

• If new ‘loss’ may bump into objects

• Lack of awareness of one side

• Problems following lines, scanning

• Reading - from ‘blind’ area or into ‘blind’

side

Help available?

• Advise on scanning

• Practice change of lines

• Limited success with prisms

• Monitor progression - rarely in progressive conditions. Ensure effects to brain tissue not progressive

• ‘Hidden loss’ - emotional support

Extent of field

60

75

10060 (one eye)

Practice makes

Perfect

CataractWhat is it ?Cloudiness of the human lens

Present at birth or may develop in

childhood

Causes/ Risk Factors1/3 ‘just happen’

Genetics - family history

Infectious causes- rubella (the most common), chicken pox,

cytomegalovirus, herpes simplex, herpes zoster, poliomyelitis,

influenza, Epstein-Barr virus, syphilis, and toxoplasmosis

Syndromes - Downs , Edwards, Trisomy 13

Trauma - Physical, metabolic, substance related

Treatment

• Surgical treatment - if possible

under 2 months of age

• Children’s visual development is dependant on a good retinal image

• Correct vision - lens inside eye (IOL), contact lenses, glasses

• Success depends on ‘aggressive’ treatment

Is it or isn’t it• Congenital cataracts present at birth but may not be identified ‘til later

• Some cataracts are static, but some are progressive.

• Anterior polar cataract and nuclear cataract are usually static

• Cataracts that progress usually have better prognosis as only begin to obstruct the vision after the critical period of visual development .

• Not all cataracts are visually significant. If opacity is in the visual axis it usually significant and requires removal. > 3 mm in diameter are generally considered visually significant.

• A study by the Department of Pediatric Ophthalmology of the Wills Eye Hospital concluded that, in terms of the risk factor for amblyopia difference in refraction more important than the cataract size .Patients Anisometropia of 1 D or more are 6.5 X more likely to be amblyopic.1

Infant Aphakia Treatment Study

Symptoms

• If uncorrected or surgery complicated glare - note raising of hand to head and covering one eye.

• Difficulty with detail and mobility due to

generalised loss of vision (frosty window)• Dressing difficulty due to alteration of

colour perception.

Symptoms

• Uncorrected cataract may have limited effect on acuity but markedly affect contrast

• Contrast sensitivity measures the ability to see faded targets

Practical issues

• Support lens use and patching

• Good localised lighting - PL types

• Filters, tints - UV protection

• Sports caps - glare

• Look out for capsule formation and screen for glaucoma

Other long term issues

• Glaucoma ( up to 50% cases)

• Capsule clouding

• Retinal detachment

The world is not bold

We don’t just see in black and white

Contrast tests help us consider how well a person ‘see’.

Seeing disabilities

‘Normal’ Curve

Good acuity but reduced contrast

Reduced acuity and contrast

Pelli-Robson chart

• The chart consists of letters organised into groups of triplets.

• There are 2 triplets per line• The letters within a triplet all

have the same contrast• All letters are the same

‘spatial frequency’ ( in plain English - the same size !)

Pelli-Robson chart

• Valuable as records contrast %

• Enables estimate of function

• Reserves - 10:1 fluent or 3:1 ‘spotting’

• E.g.. Top two lines = – 90% to 31% severe loss, consider non-

optical devices

If Time ? Practice makes

Perfect

Skimming the surfaceLocal professionals• local optometrist• local hospital - Eye Clinic Liaison/ Consultant secretaries

Letter/ phone call to Orthoptic department

Web resources• http://biomed.science.ulster.ac.uk/vision/-Visual-Acuity-What-do

es-it-mean-.html

• www.rcophth.ac.uk/about/public/childrens-eye-info

• www.goodhope.org.uk/Departments/eyedept/

• www.cafamily.org.uk

That’s all ?

• Thank you for listening

• A list of websites that may be helpful is listed in your handouts (with some additional information )

• m.bairstow@vision2020.uk.org.uk