Effect of mental retardation and motor disability on testing with visual acuity cards.

The visual acuity of 77 children (aged between 1 1/2 and eight years) with cerebral palsy and mental retardation was tested using acuity cards. Results varied by no more than one octave in 79 per cent of the cases. The median acuity of children with severe motor disabilities was lower and the variability from test to test was greater than for those with mild motor disabilities. Grouping the children roughly according to degree of mental retardation, the more retarded group tended to be more visually disabled and vary more from test to test. In general, day-to-day variability was greater than within-day inter-observer variability. The use of acuity cards to evaluate visual acuity in severely disabled and mentally retarded children, whose acuity is difficult to evaluate with conventional acuity tests, is a useful alternative method.