Transcript Topic 2: The Low Vision Evaluation - Learning

Low Vision Evaluation
Ms MB JAN- 24/01/2012
Content
1.
2.
3.
The difference between a low vision
exam and a regular exam
The Case History
Evaluating visual performance
4. Evaluating visual performance
i.
Visual acuity
ii. Visual field evaluation
iii. Contrast sensitivity
iv. Colour vision
5. Objective refraction
6. Subjective refraction
7. Ocular health evaluation
OUTCOMES
At the end of this lecture, learners should
be able to:
 Discuss
the importance of a case history
specifically for a low vision patient
 Discuss specific questions that will be asked
to a low vision patient
 Describe the different techniques and
charts used to measure a low vision VA
(near, distance, aided, unaided etc.)
 Discuss
the need for evaluating visual
fields in a LV patient
 Discuss methods and techniques for
evaluating visual fields in a LV patient
 Discuss the need for evaluating contrast
sensitivity in a LV patient
 Discuss
the need for evaluating colour vision in
a LV patient
 Discuss the methods and techniques used for
evaluating colour vision in a LV patient
 Discuss the objective refraction techniques
available to the low vision optometrist
 Discuss the technique and implications of
radical retinoscopy
 Discuss
the method used for refracting a low
vision patient
 Analyze a low vision case based on a history,
and then decide on and describe the most
appropriate evaluation routine for a specific
patient
 Distinguish between a low vision refraction
routine and a normal refraction routine
 Explain the concept of JND (just noticeable
difference) and be able to use it to test a low
vision patient
The pre-evaluation information sheet
It sets clear boundaries on what you will
be able to do
 Draw up your own sheet in practice

Information sheet
1.
2.
3.
The appointment duration
Schedule appointment around a time
when patient’s vision is stable
Bring with old glasses, magnifiers – even
if not usable anymore
4.
Think about specific problems the patient is
experiencing
5.
Start thinking in terms of goals – write down
what you would like to achieve
6.
Bring along special materials he/she want to
be able to use (E.g. books)
7.
Bring along a report from the
ophthalmologist
8.
Follow-up visits or training sessions with
equipment may be necessary
9.
State that there are no miracles, we will use
your remaining vision effectively
The difference between a low vision
examination and a regular exam
Give the differences and explain
each point given
Disadvantages of using phoropter

Why not phoropter?
Case History
NB.Very important, It has to be even more detailed
The patient interview

The successful patient interview has 3
functions (Cohen-Cole)
◦ Gathering data to learn about the patient’s
problem
◦ Developing rapport, and responding to the
patient’s emotions
◦ Educating patients about their problems, and
motivating them to adhere to the prescribed
treatment
Interview techniques
Both parties should be seated at eye-toeye height
 Seating should be comfortable
 Control lighting – not too dim or bright
 Carefully observe the patient

Use both open-ended and specific questions
 May be emotionally charged
 Note taking should be done subtly

Be alert to inconsistencies
 Take sufficient time that patient doesn’t feel
rushed
 BUT keep it brief – old people tire more
easily
 Use positive language
 Question in a friendly, enthusiastic manner

Adjust pace to that of patient.
 Don’t use medical jargon, explain patient’s
condition if they do not understand it
 Never give false reassurances
 Primary aim is to help patient – don’t fear to
be inquisitive – but respect privacy too!

The purpose of the case history
Why is it important to take LV
case history?
The real questions you want answered
are:
1.
2.
3.
What does the patient want?
What does the patient need?
What is the real reason for the patient’s
visit?
Information required
1.
Basic identifying information
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2.
Name, address etc
Who accompanied the patient?
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Support system / self-sufficient?
Relative, friend, counselor, teacher etc
Contact person
Provide insight into history
3.
Referral source
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4.
Send thank you note
Reports
Diagnosis of eye condition
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In patient’s own words
See if patient understands condition
Begin with patient education on problems.
Visual history
a. Duration
b. Previous care
c. Nature of vision loss (congenital or acquired?
Stable or progressive?)
d. Fluctuation of vision
e.
f.
g.
h.
i.
Problems with color vision
Is there a preferred eye?
Problem with glare or lighting?
Current glasses / low vision aid
Current visual capability (specific task-related
questions)
i.
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Smallest print read?
Newsprint
Headlines
Large print
ii.
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iii.
iv.
j)
Able to watch television?
What viewing distance?
Size screen?
Can you recognize faces at a distance?
Can you see well enough to get around?
Family visual history
5. Medical history
a) Undergoing treatment for medical condition?
b) Does the patient have a disease with known
ocular implications?
c) Is there medical problems that might affect
the use of a LVA? (stroke)
d) Family history
e) Allergies and drug sensitivities
f) Medications (many systemic drugs have
ocular side-effects)
6. Employment or school history
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7.
Investigate the effect the visual loss has on the
work/school performance
Investigate the use of appropriate devices to
alleviate problems
Some older people might want to continue their
education
Avocations
◦
Hobbies or activities
8. Social assessment
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Does the patient live alone or with family?
How is daily life affected by the vision problem?
Does the patient have a support network?
Is the patient’s independence threatened?
10. General appearance of patient
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Well groomed, clean or untidy?
Food stains – cannot see that level of detail
Poor grooming - emotional disorders such as depression
Walk without assistance?
Mobility
Does the patient look ill?
11.
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Patient goals (Chief complaint)
Possibly the most important part of the case
history
Allow a full elaboration of the visual
disabilities
Patient’s new problem should be fully
investigated

After the patient has completed a list of
complaints, several issues should be
addressed regardless of the patient’s failure
to mention them
a.
b.
c.
d.
e.
Distance vision
Near vision
Orientation and mobility skills
Glare
Lifestyle
External evaluation
Some do this just after VA’s, but depends
on circumstances. Give an example
 Brief look into the eyes, do not shine
bright lights into the eye
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Note the following about the eyes:
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Position of eyes (strabismus)
Pupil – size, reaction to light, appearance,
Cornea – opacities: size, density, position
Lens – opacities, position (especially IOL)
Motility – strabismus, nystagmus, restrictions
Binocular dysfunction is usually of secondary
importance
Evaluating visual performance
Why?
Compare with normal performance, or
accepted standard (eg driving regulations)
 Set a baseline for monitoring the
condition
 Quantify the patient’s own subjective
impression of visual performance

Early detection and diagnosis of (other) visual
disorders
 Assessment of the benefits of an intervention
(medical, surgical, rehabilitation) program
 Predicting visual function in every day tasks

Visual acuity
Visual acuity
1.Why do we want to accurately measure acuity?
2. Limitations of VA measurement
3. Factors affecting VA measurements
4. Distance Visual Acuity
5. Near Visual Acuity
Why do we want to accurately
measure acuity?
i.
ii.
iii.
It establishes a baseline from which to
monitor pathology
Used to predict the magnification level
of the optical devices that will be
required to achieve the patient’s goals
Often requested by other agencies to
establish legal blindness, driving
privileges, job eligibility etc.
Limitations of VA measurement
i.
ii.
iii.
The clinical acuity does not give an
accurate indication of the functional
acuity. Explain
Clinical measure of person’s ability to
read letters under controlled
circumstances
It doesn’t always correlate with daily
activities
iv.
v.
Function can be influenced by differences in
contrast sensitivity, glare sensitivity,
motivation and numerous other factors
VA can vary due to test setting, illumination,
doctor-patient relationship and target
contrast
Factors affecting VA measurements
How does each of the following factors
affect VA measurement?
i.
ii.
iii.
iv.
v.
vi.
vii.
viii.
Lighting
Optotype
Mental state of the patient
Instructions to patient/attitude /
encouragement
Glare recovery
Educational level
Recognition/memory/speech
Motivation
Distance Visual Acuity
a.
b.
c.
d.
VA Notations
Acuity chart design
Currently used charts
Measuring distance VA
a. VA Notations
1.
Snellen
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2.
3.
4.
Either metric or imperial
We use imperial (feet)
LogMar (logarithm of the minimum angle of
resolution)
Decimal: Snellen fraction
Angular (specified in minutes of arc)
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Not used clinically
b. Acuity chart design
The following aspects of chart design can be
considered
i.
Optotype –
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style of print and selection of letters
Should yield equivalent results to Landolt C
Number of letters per row
ii.
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Equivalent – equal task progression
5 good clinically
Sequence of Letters
iii.
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not form words/part of words
Optotype Size
iv.
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0.1 logarithmic progression of character size
Accurate measurements at both standard and
non-standard test distance
Letter spacing
v.
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systematic
c. Commonly used charts
1.
Feinbloom Number Chart
Refer to your notes for advantages and disadvantages
Of this chart
2. Bailey-Lovie
Advantages
 logMar format
 Equal number of
letters at each line
 Can be used at any
test distance
3.
4.
Projected cards
Other
1. Lighthouse distance acuity card (available in our
clinic)
2. Lighthouse symbol cards
3. Designs for vision pediatric picture chart
4. University of Waterloo Chart
5. ETDRS chart
d. Measuring Visual Acuity
Use special low vision charts
 Use a 10feet / 3 m working distance, or
less
 Emphasize residual vision
 Offer encouragement and realistic
feedback

Watch for and encourage eccentric viewing
 Let the patient attempt to read all letters on
the chart, and look for scotomas
 Record as Snellen fraction, e.g 10/700
 To convert between feet and meter, divide by
3.25 (feet to meter) or multiply by 0.3 (meter
to feet)
 Always measure the acuity correctly: “less than
6/60” is unacceptable

Recording VA Measurements
Can have a measurement recorded as
BEO (both eyes open) – distinguish from
OU
 Record the fractions read:
 10/240 + 2 of 10/200 + 1 of 10 / 180

If the patient is unable to identify any
optotypes, which designations are
you going to use?
Near VA
The measurement of Near VA is a very
important part of low vision
 Most low vision patients struggle with
reading, so magnification for near tasks is
vital.

Near VA
a.
b.
Specification of Nearpoint acuity
Measuring near acuity with the M
system
a.
Specification of Nearpoint
acuity
M notation
i.
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Method of choice
Metric notation
Represents the distance in meters at which the
target subtends an angle of 5’ of arc
1.00M subtends 5’ at 1m
Consistent, meaningful, flexible testing distance
N notation
ii.
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Point size of lower case Time Roman print
Standardized so that each point is 0.18 mm on
the printed page
N10 is twice N5
Quite valid
Necessary to specify both test distance and
target size
Point type
iii.
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Actual print size in printers point notation
Size of slug, but not actual print size
Not a very good system
Reduced Snellen
iv.
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Characters subtend the same angle indicated by the
designated fraction at 20 feet
Specified test distance
Not 20 units, not a standard angle at 20 distance units
Cannot be used at any other distance
Useless - inflexible
Visual field evaluation
This another important aspect in low
vision patient
 Desirable to test all patient’s fields, but
not always possible or practical

Instruments and techniques
1. Confrontation
test
◦ Only a gross estimate of the peripheral field
◦ Screening method
◦ Use light as a target
2. Amsler grid
What is it?
a.
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Hand-held chart used to evaluate central 20° of vision
Can identify early changes like metamorphopsia or small
central scotoma
What does it look like?
b.
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20 blocks x 0.5mm each
c.
How does it work?
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“Place a finely quared chart before an eye suffering from
an affection of the central region of the retina, and the
patient will immediately point out spots and distortions
which affect his/her vision”
Measures the central 20° of vision if the chart is held 2830cms from the eye
d.
i.
Types of charts
Standard chart *
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ii.
Diagonal lines*
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iii.
Use with central scotoma
Red on black standard chart
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iv.
Every case, and usually sufficient
Colour scotoma
Spots only
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Reveals scotoma (no lines to be distorted)
v.
Parallel lines
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vi.
Parallel lines for reading
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vii.
Use horizontally and vertically
Shows metamorphopsia
Allows a more minute evaluation of reading area
Standard block with smaller reading area
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Minute examination of juxta-central area
Rectangle shows limit of fovea
e. General method
Testing distance
 Optimal refraction
 Clean, clear, well-lit chart
 No ophthalmoscopy etc prior to evaluation
 Do monocularly and then BEO to check for
interference/suppression
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What chart?
◦ Start with grid
◦ Then use lines and spots
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Do monocularly and then BEO to check for
interference/suppression
f.
i.
ii.
iii.
iv.
v.
vi.
Questions asked
Do you see the white spot in the centre of the
squared chart?
4 corners? 4 sides? Whole of the square?
Network intact?
Lines straight + parallel?
Anything else?
Plotting the distortions?
Colour vision

Pathological conditions like glaucoma and
ARMD can cause changes in colour vision,
so it is necessary to evaluate this.
◦ City University (not available in our clinic )
◦ Isihara
◦ Farnsworth D15
Isihara
Tests for colour
deficiency of congenital
origin
 Limited value in LV

Farnsworth D15
Available in our clinic
 Check functional tests
notes

Refraction
Always obtain the best possible refraction with the
best possible VA – to give the lowest magnification,
why?
Objective refraction
1.
Autorefractors
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2.
Limited use, due to media problems or
eccentric viewing (off axis fixation)
Previous glasses
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Can be a good starting point
Just make sure patient is using own Rx!
Patient might have had ocular surgery since
glasses were prescribed
3.
Keratometry
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4.
Useful with astigmatism – amount and
orientation of cyl
Patient may have difficulty fixating
Can be helpful in detecting irregular corneal
surfaces or irregular astigmatism
Retinoscopy
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◦
Very useful, especially if patient is a poor
responder
May be necessary to use radical retinoscopy
Retinoscopy
◦ Always do the ret in a trial frame
◦ If there is no initial response or no reflex is seen,
try using very large lens changes like +/- 5D, +/10D, +/- 20D
Radical retinoscopy
Radical retinoscopy means that the
working distance is drastically reduced (as
close as 10cm)
 Radical retinoscopy can also mean
deliberate off-axis scoping to use any
visible reflex – this will induce unwanted
cylinder, but the results can be potentially
valuable

Subjective refraction
1
2
3
4
5
General conditions
The trial frame
The JND (just noticeable difference)
Spherical refraction
Cylindrical refraction
General conditions
Use a 10feet or less working distance
 Use full illumination unless otherwise
indicated (e.g. patient with
achromatopsia)
 Use the low vision chart in subjective
refraction
 Always do a trial frame refraction

The trial frame
Why do we use it?
The refraction itself
Use standard methods and background knowledge to
refine cylinder axis, power and sphere power
The JND (just noticeable difference)
Essential concept
 The smallest dioptric step that a patient is
able to discriminate
 It is senseless and frustrating to use
0.25D steps when (because of the visual
impairment) the patient can only notice a
1.00D change
 Use the 10-feet equivalent as a rough
starting point for JND

If the best VA is 10/100, the JND will be 1.00D
 10/50 = JND of 0.50D

Spherical refraction
Use the tentative result from your
objective refraction as a starting point
 Determine the JND-lens, and check the
sphere value with that
 “Better with the lens, or without it”, not “one
or two”
 Patients may have a poor, slow, variable
response – could be due to pathology

Cylindrical refraction
Check the axis using a hand-held Jackson
Cross-cylinder of +/- 0.50D or +/- 1.00D
if possible
 You can also use rotation to blur/clear
and let the patient rotate the axis
her/himself
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Cylinder power is checked in the normal way
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Double check cyl power with direct
comparison (with or without) – if no
subjective or objective improvement, it is not
necessary to prescribe

Finally, double check the spherical component
again – use bracketing (eg +0.50 and -0.50
should blur equally)
Ocular health evaluation
OPTIONS:
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Ophthalmoscopy
Keratometry
Tonometry
Slitlamp
Von Herick
Dilated fundus exam
Binocular indirect ophthalmoscopy