Visual function assessment in low vision

VISUAL FUNCTION
ASSESSMENT IN LOW
VISION PATIENT
STUTI J. JARIWALA

BIOGRAPHY
 STUTI J. JARIWALA
 INTERNSHIP ( KESHVI EYE HOSPITAL,
SURAT )
 B.OPTOM ( BHARTIMAIYA COLLAGE
OF OPTOMETRY, SURAT)

PURPOSE OF LOW VISION
ASSESSMENT
 The purpose of low vision assessment is to assess the residual, present
vision and correlate it with the individual‟s social, educational, vocational
and other needs, and to identify ways and means to enhance the residual
visual functions.
 Low vision assessment is a result oriented procedure, at the conclusion of
which, the examiner should have a clear perspective of what needs to be
done.

What is low vision??
 WHO definition:
 A person with low vision is one who has impairment of visual functioning
even after treatment and/or standard refractive correction, and has a visual
acuity of less than 6/18 (20/6) to light perception or a visual field of less
than 10 degree from point of fixation but who use or potentially able to use
vision for the planning and/or execution of a task.

STEPS OF LOW VISION ASSESSMENT
1. Observation and history taking
2. Slit-lamp examination
3. Evaluation of vision
1. Distance
2. Near
3. Pinhole
4. Refraction
5. Amsler grid
6. Contrast sensitivity
7. Glare test
8. Laser interferometry
9. Visual field
10. Binocular vision
11. Color vision

1. OBSERVATION AND HISTORY
TAKING
 Observing the patient‟s behavior and his physical status can provide an
insight to the severity of the problem.
 Observation begins in waiting area and continues into consulting room.
 A concise history that can provide a fairly accurate idea about diagnosis,
an information about the visual activities that present difficulties to the
patient and what are patient‟s expectations should include the following
questions.

 Date of onset and progression of visual field loss.
 The details of the diagnosis, investigations undergone and type of
treatment taken.
 Age, educational status and professional requirements of the patient.
 Low vision is more for near or distance or both.
 Patient prefers more or less light.

 List of the visual activities that present difficulties to the patient, including
the ability to move independently.
 Medical, social and psychological build of the patient.
 Exact requirements of the patient in terms of near, intermediate or distance
vision should be enquired into.

2. SLIT-LAMP EXAMINATION
 The ocular examination should include anterior segment bio-microscopy
and detailed posterior segment evaluation with indirect ophthalmoscopy
and focal illumination techniques with 90 or 78 D lens.

3. EVALUATION OF VISION
 For distance
 The visual acuity assessment begins with determining the distance acuity
of the patient.
 The procedure involves showing the patient large size numbers on sheets
from a certain distance and asking him or her to identify them.
 Optotypes, single-letter chart gratings and crowded letters of different sizes
may be shown to the patient alternatively.

 Vision charts designed for low vision are hand held or movable rather than
fixed or projected. Each line contains several characters so memorization
is less likely
 ETDRS charts are recommended for more accurate recording.
 Patient feel more confident when they are able to read more letters and the
start of low vision is with a positive note.

 The hand held charts avoids glare, give better contrast and can be moved
closer so that letter size is doubled.
 Record acuity with the actual testing distance in the numerator and
optotype size in denominator.
 All patients should be examined first in daylight condition
 Bailey & Lovie chart are the logarithmic scale. Main advantage of chart is
that it's near vision equivalent; greatly simplify the process of calculating
the estimated magnification required by a patient.

 LogMar chart:
 Principle of a LogMar chart is that it uses a logarithmic scale.
 5 letters per line, there is constant size progression ratio of 5/4 and each
line is 1.25* bigger/ smaller than previous.
 Ex.1 If patient read 6/6 line so its LogMar value = 0.0
where Mar value is 1 so LogMar = log10(1.0)= 0.0
 Ex.2 If patient read 6/12 line so its LogMar value = 0.30
where Mar value is 2 so LogMar = log10(2.0)= 0.30

Pinhole acuity assessment
 Pinhole acuity test is used to assess the presence or absence of a refractive
error improvement in vision through indicates that the person may benefit
from refractive correction.

 For near
 In this step the patient identifies or reads certain typeset of a smaller size
from a nearer distance. The distance is accurately recorded. The typeset
size is denoted in M units.
 Reading acuity is the patient's ability to read a more congested and
complex typeset prints froma measured distance.
 Notation for near visual acuity:
• M- notation
• Point notation
• Jaeger notation
• Reduced snellen notation

 M – notation
 Introduced by Sloan and Habel.
 Size of letters is indicated by the distance in meter at which lowercase
letters subtend 5 min of arc at a distance of 1 m and is 1.45 mm height.
 Regular newsprint is usually 1.0 M in size.
 Near visual acuity is usually recorded in this notation as 0.40/1.0 M
where test distance was 40 cm and 1.0 M is letter size
 Most common methods of near visual acuity used in low vision care.

 Ex. If patient brings in print they wish to view.
• Measure the task size in mm.
• Measure the distance.
• Divided by 1.45 to convert into M units.
• Specify vision as M units at * distance.
 One can also go further and convert into snellen equivalent acuity for
comparisons to distance acuity.
• Ex. A patient reads a letter of 4.3 mm height at a viewing distance of 40
cm.
• The visual acuity in M notation: 4.3/1.45 = 3 M
• Near visual acuity = 0.40/3.0 M

4. REFRACTION
 Refraction should be performed for far and near. It is important to establish
the degree of refractive error, since it forms the basis of visual acuity test for
distance and near and influences the eventual power of the LVA.
 Many times, people with low vision will have improvement with just
careful refraction.

The refraction is performed objectively
and subjectively
 Objective Refraction
 Auto-refraction
 Radical retinoscopy
 Off-axis retinoscopy
 Near retinoscopy
 Keratometry or corneal topography to measure anterior corneal curvatures
and corneal integrity

 Subjective Refraction
 Trial frame, when indicated/ Halberg clip
 Just noticeable difference (JND) technique
 Hand-held Jackson cross cylinder
 Nonstandard distances
 Stenopaic slit
 Multiple pinhole lens

 An autorefractor can give an accurate starting point for subjective
refraction, especially when high refractive errors or media opacities are
present.
 Radical retinoscopy will sometimes facilitate detection or neutralization of
motion and can be helpful when media opacities are present, pupils are
small, or the reflex is dull.
 Moreover, refracting off axis may elicit a brighter reflex, especially in
patients who have high myopia.

 Using hand held lenses is more comfortable then phoropter/ lenses in trial
frame, because this allows for eccentric head or eye position most patients
require and also the examiner can watch the patients head and eye
movement during test.
 Still better are the larger aperture full frame trial lenses set.
 Retinoscopy technique:
 turn off all lights. Hold the lenses in the spectacle plane.
 Looking through the retinoscope, move toward the eye until either a „with‟
or an „against ‟ motion is clearly visible.

 Vary your working distance to verify that you have located neutrality.
 Move off the visual axis to find and reflex that might not be apparent when
flashing along the visual axis.
 Convert the working distance to diopters and substitute this amount from
the total power of the lens.
 Each meridian can be measured independently.

 For eg. +5.00 D is held in spectacle plan neutrality is observed in 90
degree meridian at 33 cm. neutrality is observed in 180 degree meridian at
25 cm.
 So Net Retinoscopy = +2.00 Dsph/ -1.00 Dcyl * 90 degree
 Net Retinoscopy = Gross Retinoscopy - Working Distance
 +2.0 +5.0 +3.0
= - +4.0+5.0+1.0

 Using the subjective refraction to refine objective fine:
 Find best sphere.
 Test for astigmatism
 Test for best sphere.

Find best sphere
 Finding best sphere with bracketing technique:
 The starting lens in trial frame should be retinoscopy finding/ Autoref
reading/ patient‟s past prescription.
 Direct the patient to look at a supra-threshold or threshold line on chart.
 The key to bracketing technique in low vision is to present the eye with
enough of a lens. Change for patient to discriminate change in a blurred.

 This involve judicial selection of their range of powers to a minimum
resulting in the find choice of a lens. This reduces the time taken
significantly.
 Amount of spherical power needed to elicit appreciable change is clarity or
blur is called as „ Just Noticeable Difference‟ lens or JND.
 The poorer the acuity the larger the JND.
 Rule of thumb denominator of 200 feet snellen acuity gives value of JND.

 Ex.1. 20/150 eye will be sensitive to a lens change of approx. 1.50 D.
 Ex.2. 20/200 eye will be sensitive to a lens change of approx. 2.00D.
 ( +1.00 Dsph. And -1.00 Dsph. sequentially) (total lens change 2.00D)
 Ex. Patient acuity is
 RE: 20/200
 LE: No Light Perception
 Retinoscopy: unobtainable
 Old glasses: unobtainable
 JND: 2.00 D

 Ask patient to compare +1.00 Dsph. to -1.00 Dsph. Patient states that
+1,00 Dsph. Is clearer place +2.00 Dsph. In the trial frame.
 Again ask patient to compare +1.00 Dsph. To -1.00 Dsph. This time with
+2.00 D already in the trial frame if the patient still prefers the plus lens to
the minus, replace the +2.0 D in the trial frame with +4.00 Dsph.
 Again ask the patient to compare +1.00 to -1.00 Dsph., this time through
+4.00 Dsph. In the trial frame.

 If the patient prefers -1.00Dsph. to the +1.00Dsph., this is called „reversal‟
and we now know that the best shere is more than +2.00 Dsph. Not less
than +4.00 Dsph.
 We can replace the +4.00 Dsph. Lens by +3.00 Dsph. And continue
refining the best sphere by letting the patient compare the JND lens.
 We have bracketed around the best sphere with stronger and weaker lenses.
In this way refractive error can be arrived quite accurately and reliably in
low vision pt.

Find the best cylinder
 After finding the best sphere, test the patient for astigmatism, refines the
axis first, then the power using a high power Jackson cross cylinder.
 The following set of JCC are needed:
 +/-0.25 for 20/20,
 +/-0.50 for 20/30 to 20/50,
 +/-0.75 for 20/50 to 20/100 and
 +/-1.00 for 20/100 and worse.
 It is essential to use strong enough cross cylinder in order to determine to
astigmatic component in the low vision in refraction.

 Axis: for testing axis, carefully line up the handle of JCC with the cylinder
being tested and proceed to test axis in the same way.
 For testing power: change the amount of cylinder by just noticeable
difference and get a reversal in the same manner keep the spherical
equivalent constant when changing cylinder power.

Retest for best sphere
 After the test for astigmatism the trial step use to retest for best sphere with
the JND lenses.
 If there is no prior indication of astigmatism error test subjectively for the
presence of astigmatism after the best sphere has been determined.
 Check for the presence of cylinder power by flipping the JCC in front of
the best sphere with its handle oriented of 45degree.
 If the response indicate astigmatism, place a JND amount of cylinder in the
trial frame at its appropriate orientation, adjust the sphere to keep sphere
equivalent constant and thus refine axis and power.

5. AMSLER GRID TESTING
 Amsler is a simple test, which helps in measuring any visual field losses in
the central field by using a special grid.
 It establishes whether patient has Central or Eccentric fixation. Patient
with central scotoma needs eccentric viewing training

6. CONTRAST SENSITIVITY
 Sensitivity to contrast is the ability of the eye to perceive the smallest
difference in luminance. In order to measure contrast sensitivity, a
procedure is used in which the subject compares the luminance of
standardized target with its surroundings .
Pelli Robson chart

 Important to find, Need for Magnification, Ability to use Optical Devices,
Lighting (Functional Adaptive Device), Dominant Eye Overall Function-
contrast enhancing techniques.

7. GLARE TEST
 Clear ocular media are required for a clear image to be formed on the
retina.
 Glare is perceived by a patient whenever light is scattered between the
source and the retina.
 This can occur at the level of tear film, camera, Anterior Chamber, lens or
vitreous.
 Many patients with reduced visual function required increased
illumination but also few of them will experience the glare.
 Example, consider a patient with a posterior sub capsular cataract a
macular degeneration.
 Glare testing can help to confirm why increasing light might not help in
the presence of a posterior sub-capsular cataract causing glare.

Method to check glare:
 The simplest is measuring the deterioration of the visual acuity or contrast
sensitivity while shining a strong light toward the patient at an oblique
angle.
 Commercially, available tests : such as the brightness acuity tester (BAT)
or the miller nadler glare tester.
 A test is considered positive if acuity drops off significantly as illumination
is increased.

Visual function assessment in low vision

8. LASER INTERFEROMETRY /
POTENTIAL ACUITY METER
 Both instruments are designed to help predict the VA potential of the
macular in the presence of media opacities such as cataract the patients
best distance Correction should be warn for the interferometer
 The potential acuity meter (PAM) projects an image of a snellen acuity
chart, adjusted for the refractive sphere, through a small, clear portion of
the lens on to the retina

9.VISUAL FIELD
 It is an important diagnostic and screening tool for patients with glaucoma,
retinitis pimentosa & many neurologic disease.
 Confrontation screening is a gross field test that should be conducted to
screen all patients.
 The design of the goldmann test is after more accurate than automated
perimetry for low vision patient.
 Macular perimetric programs that test the central 10o May disclose
scotoma that significantly affect function.
Confrontation test

Uses of visual field test in low vision care:
 To document the visual field parameter of “legal blindness” requirement
testing is often needed to determine qualification for government.
 To fulfill eligibility criteria for those states and provinces that require a
minimum visual field in order to hold a driver‟s license.
 To provide objective information about scotomas in the visual field, which
may explain unexpectedly poor performance.
 Pattern of peripheral loss can predict the need to learn safe travel skills
(orientation of mobility) & influence the plan for rehabilitation
 To follow disease progression & explain a change in function that does not
otherwise correlate with acuity or contrast tests

10. BINOCULAR VISION
 Gross assessment of ocular alignment (e.g., Hirschberg estimation).
 Sensorimotor testing (e.g., Worth four dot, stereo fly, red lens test)
 Amsler grid testing, Contrast sensitivity:
monocularly versus binocularly to determine eye dominance and the need
for occlusion.

11. COLOR VISION
 Color vision anomalies, which can significantly affect educational,
vocational, daily living, and mobility needs, can be diagnostic of specific
diseases.
 Some color vision tests e.g., Holmgren wool, D15 panel test, Ishihara's test
can help assess the functional implications of color vision loss.
ISHIHARA chart

Visual function assessment in low vision

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