Transcript The treasure of measure (Understanding the Clinical Assessment)

What do I see ?
Questions and tests
June 17th 2010
Mary Bairstow
Low Vision Services Implementation Officer
About the presentation
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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
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3
4
8
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The child 
2.
‘Synpedagog’, low
vision teacher
3.
1
5
1.
7
6
Swedish ‘model’
International Conference
on Low Vision 1990
Ophthalmologist
4. Optometrist
5.
Psychologist
6.
LV Counsellor
7.
Rehabilitation Officer
8.
Secretary
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
www.mdsupport.org/images/
retlayers.jpg
Diagram from
Rodieck, The first
steps in seeing
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?
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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 Spread
Snellen Progression
60
36
24
18
12
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 reserves
Fluent 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?
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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
60 (one eye)
100
75
Practice makes
Perfect
Cataract
What is it ?
Cloudiness of the human lens
Present at birth or may develop in
childhood
Causes/ Risk Factors
1/3 ‘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
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Congenital cataracts present at birth but may not be identified ‘til later
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Some cataracts are static, but some are progressive.
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Anterior polar cataract and nuclear cataract are usually static
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Cataracts that progress usually have better prognosis as only begin
to obstruct the vision after the critical period of visual development .
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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.
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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
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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 nonoptical devices
If Time ? Practice makes
Perfect
Skimming the surface
Local 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-Whatdoes-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 )
• [email protected]