Test for Large Illuminator Cabinet
The distance visual acuity test for the big Illuminator Cabinet is manufactured for 3 meter test distance.
Chart #250300 for 3 meters (10 feet) testing distance fits the ETDRS Cabinet, which has self-calibrating luminance levels. The recommended luminance level to be used in research projects is 85cd/m² in the US Luminance level can be chosen between 220 cd/m² and 3 cd/m².
Establish a method of communication such as naming (signing), pointing or matching. Decide with the child which names will be used to identify the symbols. When needed, train with the LEA Puzzle (#251600), Response Key Card (#251700), or Flash Cards (#251800).
Cover the line above the line to be read with a white card and ask the child/person to identify the first symbol in each line in descending order when testing binocularly. Do not point to the symbol to be read because it makes fixation easier, especially in the case of amblyopia (lazy eye).
Move down until the child hesitates or misidentifies a symbol.
Move back up one line and ask the child to identify all the symbols on that line.
If the child identifies at least 3 out of 5 symbols correctly go to the next line with smaller symbols and ask the child to identify all symbols on the line. The child may have started to focus more carefully and may be able to read that line, sometimes even the next line. Therefore say calmly “and on this line” and do not let your voice give the impression that it is too small to be read.
If the child skips a symbol, let the child read the line to the end and then ask the child to try again while briefly pointing to that symbol and say “You hopped this picture between (e.g.) ‘house’ and ball’.” What is it?”
A child with an amblyopic eye or irregular saccades may typically skip symbols within a line of symbols. If skipping symbols occurs, report whether it occurred in only one eye or in both eyes. It may be a sign of more general motor problems.
Visual acuity is recorded as the last line on which at least 3 of the 5 symbols are identified correctly.
When tested at 3 meters (10 feet) the visual acuity value is found in the margin adjacent to that line.
After obtaining good responses with binocular testing, proceed by testing each eye separately.
When testing monocularly, use the first symbol of each line or every second line for one eye and the last symbol of each line for the other eye to determine on which line to start testing. Then move to the small sets of test lines on each side and test the same way as when using the middle set of test lines. This way the child cannot memorise the chart. Use the right set of symbols for the testing of the right eye and the left for testing the left eye.
Always remember to record which test you used and at which distance. This makes the follow-up more reliable, even if the child moves to another school and will be tested by another school nurse and another doctor.
Testing at Different Distances
If the chart is used at a distance other than the usual 3 meters (10 feet), measure and record the viewing distance and the symbol size (the M value) or the visual acuity value printed at the threshold line.
To determine the visual acuity use one of the following formulas:
Note that it is incorrect to report 'V.A. 20/25 at 5feet' if the child could read the 20/25-line (3.8M line) at 5 feet. Visual acuity is in that case: 5'/10' x 20/25 = 1/2 x 20/25 = 20/50. (When using the British notation: 6/9 line at 150cm equals: 1.5m/3m x 6/9 = 1/2 x 6/9 = 6/18. When using the decimal notation 0.8 at 1.5m equals: 1.5m/3m x 0.8 = 1/2 x 0.8 = 0.4)
When the distance is one half (or one third) of the standard distance, the visual acuity value is also one half (one third) of the value printed next to that line.
In the rare cases where the child/person can read all optotypes correctly on the 2.0 (20/10, 6/3) row and none on the 2.5 (20/8.0, 6/2.4) line, the test can be moved to a slightly shorter distance to record the threshold level. At a distance of 2.76 m the visual acuity value of the 2.5 line is 2.3 (20/8.7, 6/2.6).
Always remember to write down which test you used and at which distance. This makes the follow-up far more reliable, even if the child moves to another town and therefore to an office of another doctor.
M-unit, metric unit is the distance in meters at which the reference optotype C is seen at a visual angle of 5'.
[ Instructions I Paediatric Vision Tests I Vision Tests ]
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