Measuring visual acuity
To use the software for vision screening, the computer should be set up in a quiet room which is at least 4 metres long. The ambient lighting should be "subdued" (approximately 300 lux) and care should be taken to avoid reflections on the computer screen. If possible, blinds/curtains on the windows should be drawn.
The laptop or PC screen should be placed on a suitable table and a tape measure should be used to measure 3 metres from the centre of the screen. This distance should be marked using some masking tape on the floor or by placing a desk at that distance for the children to stand behind.
NOTE: It is very important that this distance is correct at the time of testing and children resist the temptation to move closer.
It is important that children fully understand the task before attempting the test. To this end it can be helpful to get the child directly in front of the screen from where they will be able to see the letters easily. The Random chart should be used for this purpose to avoid the possibility of the child memorising the letters. Ask them to name each letter as you move the pointer from one to the next. If they are unable to name the letters, ask them to find the same shape on the matching card which was provided with the software. When you are confident that the child understands the task they should be positioned at 300cm from the screen an the test can begin.
Instruct the child to cover their left eye using an occluder or occluding glasses. Ensure that the eye is properly occluded before commencing the test.
Start by showing the child some larger letters (e.g. LogMAR 0.6) and ask them to identify each letter. The pointer can be useful for directing the child's attention to each letter in turn. If you have the remote control option it can be helpful to stand next to the child - letter size can be changed using the up/down arrow keys and the cursor can be moved using the right/left arrow keys.
If the child gets any letters wrong on the starting size, increase the letter size until they get a whole row correct. If the child cannot read the largest letters available, record "Less than LogMAR 0.8" or whatever the maximum letter size is.
If the child gets one or more letters correct, decrease the letter size and repeat the process until the child is unable to identify any letters on the row.
The final LogMAR score is calculated by counting the total number of letters that the child correctly identified. See LogMAR scoring.