Visual Adaptation Test
In children the rapid cone adaptation (adaptation to slightly lower luminance levels) is more important than rod adaptation (adaptation to really deep darkness). Therefore the speed of cone adaptation has practical meaning, children with delays in cone adaptation have difficulties in finding objects in drawers, closets, under the table and in other places where the luminance level is lower than in the surroundings.
The Adaptation Test is easy to introduce to the child: The child has to pick the white, blue and red chips in three piles, each colour in its own pile. When the child can do this at a usual room illumination, the child is asked to arrange the colours at low luminance level, so low that a normally sighted person starts to see the colours after an adaptation of 4-5 seconds.
Normally sighted children will pick the white chips first. Since this takes abut 4-5 seconds they go on separating the blue chips from the red without noticing that they are performing a test. Children with delays in cone adaptation have to stop after they have picked the white chips because they do not see the difference between the red and blue. This way, in less than 10 seconds a diagnosis of delay in cone adaptation can be made.
Cone adaptation test is important in the follow-up of children with progressive retinal changes. The most common of these is retinitis pigmentosa.
At the time when adaptation toward lower luminance levels becomes slower also adaptation to increase in illuminance may become ineffective, the child becomes photophobic. In this situation filter lenses may improve visual function in bright light and make the period of adaptation to the lower luminance level inside the house much shorter. This should be kept in mind when planning the school day. Without proper filter lenses the child may not see during the breaks and during the first half of the lessons.
For more information, see the Instructions Section, Cone Adaptation Test.