Effects of visual processing and congenital nystagmus on visually guided ocular motor behaviour

AIM The aim of this study was to compare visually guided ocular motor behaviour in children with visual processing and/or motor deficits with an age-matched comparison group and an adult group. METHOD Visual stimuli were shown to 28 children with visual processing and/or motor deficits (11 females, 17males; mean age 7y 5mo, SD 2y 9mo, range 2-14y;) and an age-matched comparison group of 213 typically developing children (115 females, 98 males; mean age 5y 8mo, SD 3y 5mo, range 0-12y). The adult group consisted of nine females and two males with (mean age of 24y 4mo, SD 4y 8mo). Individuals who had a likely diagnosis of cerebral visual impairment (CVI), an opticopathy with unknown location, nystagmus, glaucoma, or a cataract were included in the study. Exclusion criteria were a visual acuity below 0.2, a developmental age under 1 year, and the presence of brain tumours, autism, and anxiety disorders. Orientating eye movements to large cartoons were quantified using the reaction time to fixation (RTF) and gaze fixation area (GFA). A Mann-Whitney U test was used to compare the differences between groups and Bonferroni post-hoc testing was used to analyse age dependence of RTF and GFA values within the comparison group. RESULTS Individuals with CVI showed significantly prolonged RTF values; those with congenital nystagmus showed significantly increased GFA values. In the comparison group, RTF was significantly longer in children under the age of 2 years than in children aged 4 years and older (290 and 200ms respectively; p < 0.001). No developmental change was found for GFA values. INTERPRETATION Increased RTF values in individuals with CVI relate to visual processing deficits. The data suggest that visually guided ocular motor responses mature during the first 3 years of life.