Download Visual Acuity

M A N A G I N G P A T I E N T R E Q U I R E M E N T S D U R I N G V I S U A L
ACUITY
U S I N G T O O L S F O R T E S T I N G D I S T A N C E A N D N E A R
VISUAL
ACUITY
 HAND HELD CARD
S N E L L E N S C H A R T
D I S T A N C E C O R R E C T I O N A N D O C C L U S I O N
Factors governing Normal vision (6/6)
 Both eyes in alignment (extraocular muscles
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functioning)
Clear cornea
Clear lens of the eye
Clear ocular media (aqueous and vitreous)
Intact retina, optic nerve, visual pathway
What is Visual acuity?
 The resolving power of the eye used to assess and
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quantify the eye’s ability to resolve varying letter
sizes.
Visual acuity is a measurement of central vision only.
Assessment of total visual system from cornea to
occipital cortex.
Visual acuity can be tested for both distance and
near vision.
Distance visual acuity is the most common test.
Why need a visual acuity test?
• Diagnostic tool
 Baseline data
 Measures progression of disease
 Evaluates treatment
 To measure the patient’s progress visual acuity must
be assessed at every presentation.
Patient Requirements
 Patient’s co-operation
 Patient’s comprehension of what is required
 Ability to recognise images used on the various
charts (letters, numbers or pictures)
 Distance correction (glasses or contact lenses)
Standard Test Distances
 Distance visual acuity (DVA)
 20ft or 6M is equivalent to optical infinity
 Near visual acuity (NVA)
 40cm
Types of Distance Visual Acuity Charts
 Wall charts
 Testing VA in literate adults
 Printed on cardboard and mounted on a wall
 Well-suited for vision screenings and doctors’ offices
 Variations: Tumbling E chart, Landolt C chart, Bailey-Lovie
chart
Examples of visual acuity charts.
(A) Snellen chart. (B) Landolt C chart. (C) Illiterate E chart.
Tumbling E Chart
Bailey-Lovie Chart
Hand-held visual acuity cards
Primarily for children in vision screenings
Simplest form is the letter E in different sizes
printed onto hand-held cards
Free space testing
Visual acuity by Hand held card
Near Visual Acuity
 Testing the VA at close range (usually 40cm)
 The purpose is to detect people with near vision
difficulties (e.g., uncorrected high hyperopia,
accommodative dysfunction)
 In patients over 40 years old, the reduced near visual
acuity is one of the symptoms of presbyopia
Near Vision Charts
 Types
 Reduced Snellen Acuity card
 Test distance at 16in (or 40cm)
 Jaeger Acuity Card
 Point system
 M notation
Bailey-Lovie Reading Card
Lea Symbols
The visual acuity categorized (10th Revision of the WHO International
Statistical Classification of Diseases).
1 Good vision = 6/6 to 6/18.
2 Low vision = 6/24 to 3/60 (CF3m).
3 Blind = 3/60 (CF3m) to PL (perception of light).
4 Blind to light - NPL (no perception of light).
Legal blindness is defined as visual acuity (vision) of 20/200 (6/60) or less
in the better eye with best correction possible.
In many areas, people with average acuity who nonetheless have a visual
field of less than 10 degrees (the normal being 180 degrees) are also
classified as being legally blind.