Nandipha Maci Ruqaiyah Peer Seyuri Bisetty Andile Ngema
What is visual acuity?
Quantitative measure Routinely performed to measure the eye’s ability to distinguish the details of an object Ability to resolve black symbols on a white background at different distances Represents the smallest font that can be read Done at distance and near
Why is distance VA important in a LV exam?
The assessment begins with determining the distance acuity of the patient. Starting point in the process of achieving the target goal. Aids in the determination of magnification required for prescribed optical devices Assess eligibility for low vision services To monitor progression of certain ocular conditions.
Types of distance VA charts
LogMAR chart Snellen chart LVRC flip chart BRVT charts
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Why the logMar chart is The Gold standard than Snellen Chart
The logMar chart is preferred in low vision VA testing because: Shows proportional spacing between each letter and each line It allows examiners to be able to explain visual acuity using a Single number Consistent number of optotypes in each line (5)
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PROCEDURE OF ASSESSING DISTANCE VISUAL ACUITY
1. Always start with monocular visual acuity and record separately. 2. If patient reads 5 letters in a row, record the LogMAR unit as shown on the right hand side of the chart 3. Each letter on a line of the LogMAR chart contributes 0.02 log units. The higher the LogMAR VA the worst the VA is. 4. If patient read 4 letters only in a row, then add 0.02 to the LogMAR unit on the right of the chart 5. 5. That is if the patient reads at 4m if they cannot see at 4m you half the distance and add 0.3 @ 2m to your logMar value and 0.6@ 1m.
Demonstration on How To Test visual acuity at Distance in a Low vision Patient
Video here of logmar chart VA
Calculations and Recording
There are two methods on how you calculate your VA. Patient was able to read at 1m one letter at the 0.8 line on the logMar chart and read four incorrect letters . Method 1 LogMar = 0.8 + (0.3x2) + (0.02x4) = 1.48 Converting To Snellen Equivalent Visual Acuity Mar = 10^1.48 = 26.30 26.30 x 6m = 158 VA = 6/158 Method 2 LogMar = 0.8 + (0.3x2) – (0.02x1) =1.48 26.30 x 6 = 6/158
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Things to make note of when taking VA:
Type of illumination The chart used Posture : Does the patient present with a head tilt? Use of eccentric viewing? Aided or unaided?
What are the implications of pinhole VA?
If VA improves with pinhole - indicates that the patient will benefit from a refractive correction. If the VA does not improve - implies the presence of possible pathology or amblyopia. If the VA gets worse - the patient could have media opacities present and multiple pinhole VA should be taken.