Tests for Illuminator Cabinet
#271200 and #271300
Tests #271200 and #271300 are used with the small lightbox (#ESV1500 or #ESV1200), which has diodes based even luminance. The covering card is easy to hold between the test and the frame of the lightbox.
For the small lightbox there are tests for 4 meter (13 foot, #271200) and 3 meter (10 foot, #271300) distance with two groups of numbers on the lower lines. The use of a covering card is easy on the lightbox since it can be held between the test and the frame of the lightbox.
First test binocularly. Ask what is the first number on each line in descending order when testing binocularly.
(Pointing is no more allowed because it may improve the visual acuity http://whqlibdoc.who.int/hq/2003/WHO_PBL_03.91.pdf.) Make sure that the covering card is not too close to the line to be read and does not create a shadow.
Move down until the child/person hesitates or misidentifies a number.
Move back up one line and ask the person to identify all numbers on that line. If this is successful move down and ask the person to read the line where the error was made.
Visual acuity is recorded as the last line on which at least 3 out of 5 numbers were identified correctly. If only 2 numbers were correctly recognized, the value is that of the previous line +2, i.e. if the person read 2 correct on the 20/25 (6/8, 0.8) line, visual acuity is 20/30 (+2) (6/9 (+2), 0.63 (+2).
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).
Visual acuity measured with crowded symbols approximates the smallest text size that the child will be able to read. It is NOT equivalent to the print size used in learning because nobody likes to read at the level of threshold. We usually read texts that are 3-10 times larger than the threshold size.
After binocular testing test each eye separately.
If a chart is used at a distance other than the usual 3 or 4 meters (10 or 13 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:
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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