Visual and intellectual disability
The severity of visual impairment varies in different types of intellectual disability.
Generally, the more severe the intellectual disability is the more severe is also visual impairment.
The largest group of infants and children with a genetic cause of intellectual disability are children with Down syndrome. Visual problems of these children are well known: large refractive errors are more common than in typically developing children, accommodation is weak or lacking in hypotonic infants and visual acuity seldom develops to normal level. Since these deviations from the norm affect early development, they should be diagnosed during the first few weeks of life. Infants should get their eye glasses fitted for near vision because their visual sphere is limited and early learning occurs within their arms reach.
In most countries, there is no tradition of treating insufficient accommodation in infancy and early childhood, and treatment of strabismus is commonly postponed in children with developmental delay. This results in poor visual acuity at near in hyperopic children, and delays in communication and learning.
Here is a video that shows an infant react to being able to use her vision with proper eye glasses:
If children do not get their eye glasses early, they are accustomed to blurred images and may not accept their glasses when they start school. Compensation of poor accommodation with usual near correction (“reading lenses”) often momentarily changes infant’s behavior from sleepy and to well awake and active. Severely disabled infants may need several exposures to a sharp image on their retinas before they become aware of visual information.
Children with intellectual impairment need to be trained in order to be able to participate in testing. Many children will learn to respond by pointing if trained early, consistently and initially using concrete representations of the optotypes (the LEA Puzzle by Good-Lite) and shaping the response until they are able to function with optotypes alone.
The measurement of the near
vision acuities (single symbols and symbols in line) resulting in different values should alert the tester to test more carefully both ocular motor and processing functions. If the child cannot accommodate, visual acuity at near distance is worse than visual acuity at greater distances and needs to be improved with reading lenses. Few children with severe intellectual disability can perform in the near vision tests with tightly crowded optotypes.
Another child may perform well with a line test at near distance but cannot respond to it at the distance of three meters. Distance visual acuity at three meters needs then to be measured with single symbols instead. A response like this clearly demonstrates to the teacher that the child is unable to look at words, or other crowded information on the blackboard but may be able to perceive and recognize the same words at near.
Many syndromes cause changes in vision and a delay in general development. Changes may involve the eyes, visual pathways, cortical functions or all three. The next child, a boy, had a rare syndrome. It often leads to death before eight months of age and therefore this boy was not referred for early intervention until 18 months, when it became obvious that he was going to survive.
He moved by rolling quite fast, noticed objects, including low contrast objects and grasped
them. He explored the environment and reacted immediately when he heard his mother closing the zipper of her bag on the floor, rolled to the bag and opened the zipper. The mother explained that this was one of his favorite games at home.
It was obvious that he heard sounds but he did not response to words, not even his own name. His mother helped him to use the tactile sign “I want” and he seemed to grasp that it was a communicative activity combined with mother’s voice and expression. He had good visual communication with his mother and was eager to make himself
understood. Support in the further development of his communication was arranged during an evaluation week at a rehabilitation center where also his orientation in space was observed.