Clinical assessment of visual function with particular emphasis on testing methods for young children

Research during the last decades has emphasised the importance of visual stimulation during the first months of life. It is consequently of great importance to identify children with subnormal vision as early as possible in order to start treatment and habilitation. A prerequisite is that reliable testing methods are available and can reveal visual defects as early as possible. The aim of the study was to evaluate different methods for testing visual acuity in young children. The possibility of using the Preferential Looking (PL)-method as a screening test for the detection of amblyopia was assessed in 28 adult patients with strabismic amblyopia. PL regularly overestimated the visual acuity. The method is not sensitive enough for the detection of amblyopia and approximately 30% of the cases would have been missed. Contrast sensitivity could be a suitable method for the detection of amblyopia. Seven different contrast sensitivity tests were assessed in 20 adult patients with strabismic amblyopia to determine various parameters of the contrast sensitivity function. Depending on the parameters applied, all the tests investigated could be used in the detection of amblyopia Various acuity tests, have been assessed in 151 children 0-6 years of age with assumed normal vision, ocular disease usually connected with visual impairment, and strabismus.The children were divided into three age groups: 0-1 1/2 years, 1 1/2-3 years and 9 month, and 3 years and 9 months -6 years. The acuity tasks were divided into three subtypes according to the kind of stimulus used; detection acuity, resolution acuity, and recognition acuity. Children under the age of 1 1/2 years were tested with the Stycar Rolling Balls, PL (the acuity card procedure) and the detection of raisins, puffed rice and black and white sugar strands on a white and black background. It was found impossible to reliably detect subnormal vision in this age group with the tests presently available, representing detection and resolution acuities. Children aged 1 1/2 - 6 years were examined with several tests. Detection acuity with the Stycar Rolling Balls highly overestimated visual acuity, and only gave a very rough estimate of the visual function. Resolution acuity, PL, regularly led to an overestimation of the acuity values in all the three groups, especially the strabismic children. Good correlation was found between the different recognition tests in line. Slightly better values were obtained with single optotypes, a sign of crowding. Different acuity values were obtained depending on whether detection, resolution, or recognition acuity was tested. Reliable visual acuity values can only be obtained when visual acuity can be assessed with a recognition test using lines of letters or symbols. However, the detection and resolution acuities give valuable information about the childs total visual behaviour. Contrast sensitivity function was assessed, in children 3 years and 9 months - 6 years, with the LH contrast test, and the ability to detect raisins, puffed rice, and sugar strands. It was found that a separation between the subjects with subnormal vision due to ocular disease and strabismic amblyopia in comparison with the subjects with normal vision could be made with the LH - contrast test, but not with the other tests. Key words: amblyopia, children, contrast sensitivity, crowding, detection acuity, linear tests, ocular disease, preferential looking, recognition acuity, resolution acuity, single tests, strabismus, visual acuity, visual impairmen