Chart for Vision Rehabilitation
LEA NUMBERS® developed by Lea Hyvärinen, M.D.
The LEA NUMBERS® Chart for Vision Rehabilitation is designed for examination of severely visually impaired children and adults. The largest optotypes are 50M in size corresponding to 1/50 (20/1000, 6/300, 0.02) and the smallest optotypes are 1M in size corresponding 1/1 (20/20, 6/6, 1.0) at a distance of one meter. The test comes with a one meter cord to maintain the proper testing distance.
Start testing binocularly. Ask what is the first number on each line in descending order to quickly approach the threshold area.
(Pointing is no more allowed because it may improve visual acuity http://whqlibdoc.who.int/hq/2003/WHO_PBL_03.91.pdf.)
Move down until the child/person hesitates or misidentifies a number. Move back up one line and ask the child/person to identify all the numbers on that line. If the child/person identifies at least 3 out of 5 numbers correctly, go to the next line with smaller numbers and ask the child to identify all numbers on that line.
If the child/person skips a number, let the child/person read the line to the end and then ask him/her to try again while briefly pointing to that number. A child/person with fixation problems or irregular saccades may skip numbers within a line of numbers. Report this finding.
Visual acuity is recorded as the last line on which at least 3 of the 5 numbers are identified correctly. 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 number of each line or every second line for one eye and the last number of each line for the other eye to determine on which line to start testing close to the threshold value.
If the client has profound low vision, the lowest rows of the test can be used as a near vision test. The distance of 25cm is the most practical distance because calculation of the visual acuity values is simple. They are ¼ of the value printed next to the last line read. (To calculate ¼ of a Snellen value, you multiply the denominator by 4.)
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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