Ocular Motility Patterns in Intellectual Disability: Insights from the Developmental Eye Movement Test

Abstract

Purpose: To measure the ocular motility parameters of the Developmental Eye Movement (DEM) test objectively, with an eye tracker in subjects with intellectual disability (ID). Methods: The DEM test was performed on 45 subjects with ID, while their eye movements were recorded with an eye tracker. Some objective parameters of ocular motility were obtained through each subtest (A, B, and C) of the full DEM test. Results: There was a significant positive correlation between the saccadic speed (cc: 0.537; p = 0.001) and length (cc: 0.368; p = 0.030) of both eyes for the same subject. People with a higher percentage of ID exhibited a greater number of fixations, saccades, and errors, and took longer to perform the DEM test than those with a lower ID percentage, who had greater numbers of these parameters than subjects without ID. Subjects without ID exhibited faster saccades, with a higher amplitude, than subjects with ID. Conclusions: The eye tracker quantifies ocular motility parameters involved in the DEM test in subjects with ID. Both eyes’ movements in subjects with ID were conjugated, exhibiting saccades of the same length and speed. All parameters were different in subjects with ID compared to those in subjects without ID, so normative tables specifically for subjects with ID are necessary.