1 Visual Acuity Testing CMSft. Lynn Lawrence, CPOT ... - SECO 2011

Visual Acuity Testing
CMSft. Lynn Lawrence, CPOT, USAF (Ret.)
This course will discuss evaluation of the visual ability of the eye. It
will cover basic methods of acuity testing . This course also will present
the procedure for the Amsler grid, contrast sensitivity, color plates and
stereo testing.
CourseObjecti
ve1
CourseObjecti
ve2
Demonstrate Methods of
the proper acuity testing
methods of will be
measuring
visual acuity on
a patient.
discussed.
CourseObjecti
ve3
Procedure for
Amsler grid,
contrast
sensitivity,
color plates
and stereo
testing will also
be presented.
I. Normal Vision (5 mins)
a. What does “20/20” mean?
II. Testing Distance Vision (5mins )
a. Converting meters to feet
b. Pinhole acuity test
III. Testing Near Vision (5 mins)
IV. Low Vision Patients (5 mins)
a. Contrast sensitivity
b. Legal blindness
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CourseObjecti
ve4
Explain the
effects of glare
and decreased
contrast
sensitivity on
visual acuity.
V. Children & Preliterate Adults (10 mins)
a. Infants
b. Preschool children
c. Preliterate adults
VI. Elderly Patients (5 mins)
a. Effect of eye conditions
b. Effect of medical conditions
c. Limitations
VII. Amsler Grid Test (5 mins)
a. Indications for use
CourseObjecti
ve5
Describe
method of
testing the
central vision
with the
Amsler grid.
CourseObjecti
ve6
Describe color
vision and
stereo testing
procedure.

VIII. Color Vision Testing (5 mins)
a. Monocular vs. binocular
b. Genetic vs. acquired
IX. Stereo Testing (5 mins)
a. Binocular vision
b. Suppression
Visual Acuity Measurement
� Essential part of an ocular examination
� Requires:
• Detection of the object
• Resolving the object into component parts
• Transmitting the information to the brain
• Matching against existing memory shapes
• Communication of recognition
Acuity Charts
� Rows of different size letters
� Each subtending the same visual angle at a specified distance up to 20 feet
The Snellen Chart
� Developed 1863 by Professor Snellen
� Accepted as standard
The Snellen Chart: Disadvantages
� Some letters are easier to recognize (ex: L is easier than E)
� Patients must be literate; modifications include the Landolt rings and tumbling E
chart
� Different numbers of letterson each line and nonproportional spacing between
letters
Bailey-Lovie Chart
�� Early Treatment Diabetic Retinopathy Study (ETDRS)
� Progressive linear assessment of acuity
� Has become the standard for clinical research
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� Each row has 5 letters
� Read at 4 meters
• Acuity of 1.0=20/200
• Acuity of 0.3=20/40
• Acuity of 0.0=20/20
Pinhole
� Should be done if vision is 20/40 or less
� Allows only parallel rays from the object into the eye
Converting Meters to Feet
� 1 m = 3.28 ft.
� Divide denominator by 3
• 6/6 = 20/20
• 6/9 =20/30
Partially Sighted
� Best corrected visual acuity of 20/60 or worse in the better eye
Legal Blindness
� Best corrected eye is 20/200
� Field of vision in the better eye is less than 20 degrees
Low Vision Charts
� Feinbloom Chart
� Calibrated for use at 10 feet
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Contrast Sensitivity
� In the “real world” the eye responds to levels of luminance of a target and its
background.
� Snellen acuity charting does not reflect how the individual can visually function
when:
• driving at night
• reading in poor light
• in direct sunlight
Contrast Sensitivity Testing
� Sine wave gratings
• Electronically on a television screen
• Graphically on a chart
� Pelli-Robson Chart
• Common method of measuring contrast sensitivity
• Letter tests usually give better results than sine gratings
Infants
�� Fix & Follow (F&F)
�� Central, Steady, Maintained (CSM)
�� Response to Light (+/-)
� Opticokinetic Nystagmus Drum (OKN)
� Preferential viewing
�� VEP
Pre-School Children
� Allen picture cards
� Tumbling E’s
� HOTV
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Elderly Patients
�� Testing the vision of an elderly patient may require more time due to medical
conditions such as:
• Dry eye
• Macular degeneration
• Floaters
• Decreased contrast sensitivity
• Hard of hearing
• Confusion
Amblyopic Patients
�� Watch carefully for peeking
�� Test amblyopic eye first
�� Crowding Phenomenon: single optotype
Patients with Nystagmus
� Do not occlude
� Use a high plus lens to fog the eye not being checked
Listen to What the Patient Says
� “I can only see the letters on the left/right side.”
� Important to “push” the patient to the next line to determine if a pattern is
developing.
Factors Other Than Disease That Can Affect Visual Acuity
� Uncorrected ametropia
� Eccentric viewing
� Decreased contrast
� Large (> 6mm) or small (< 2mm) pupils
� Young or old age
� Adults
• Monetary Gain
• Attention
• Psychiatric Condition
� Children
• Want glasses
• Reaction to stress/emotional problem
• Attention
Psychological Factors That May Affect Test Results
� Attention
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� Motivation
� Intelligence
Stereo Testing
� Should be done prior to visual acuity testing
Amsler Grid
� Tests the central 20 degrees (macula)
� Each square subtends an angle of 1 0
• Macular Degeneration
• Diabetic Retinopathy
Pseudoisochromatic Plates (PIP’s)
� Ishihara
• 14, 24, or 38 plates
• Plate #1 can be read by anyone, even those with color defects
� Hardy-Rand Ritter (HRR)
• Screening test to separate those with defective color vision from those
with normal color vision
• Classifies the type of defect
• Indicates the extent of the defect (mild, medium, strong)
Farnsworth D-15
� Used to separate medium and strong color defect vs. normal
Color Vision Testing Environment
� Well-lit room
� Natural daylight, without direct sunlight
� MacBeth Illuminant C lamp
� Filtered tungsten halogen light source to provide the most accurate simulation of
natural daylight
Testing Procedures-Children
� Allow child to trace the color with a Q-tip or paintbrush.
� Do not allow the patient to touch the discs with their hands, as dirt and oil can
discolor the plates.
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