The effect of image size and defocus on children’s reflex vergence eye movements to natural images

Poster Presentation: Tuesday, May 21, 2024, 2:45 – 6:45 pm, Pavilion
Session: Eye Movements: Clinical

Bhagya L Marella1, Clara Mestre2, Stephanie A Biehn1, T Rowan Candy1; 1School of Optometry, Indiana University, Bloomington, IN, USA, 2Center for Sensors, Instruments and Systems Development, Universitat Politècnica de Catalunya, Spain

Previously, we have demonstrated anisometropia disrupting oculomotor behavior of 6-8 year-olds viewing small 2deg targets. The purpose of this study was to determine the effect of unilateral and bilateral defocus on vergence behavior using larger natural images. Vergence responses to changes in disparity in a series of 16-degree radius natural images (SYNS database) were recorded using an Eyelink 1000. The images were viewed dichoptically from a 70 cm viewing distance through active circular polarisers. They were displayed on a rear-projection screen (67deg x 41deg) using a Propixx projector. Bilateral defocus of 1.00DS and 2.00DS, and unilateral defocus of 1.00DS, 1.50DS and 2.00DS was induced by convolving these natural images with the PSF calculated for the appropriate pupil size of each participant. After aligned presentation of stimulus, a step change in disparity was presented for 1.5sec. 8 typically developing children (age:6-8 years) participated. For the 16-degree radius natural images, open-loop response amplitudes were greater for convergence than divergence at all disparities (1, 2 and 4 degrees) (p<0.001). Induced bilateral and unilateral defocus had no effect on these amplitudes (p>0.05), similar to 2-degree image size cartoons (Mestre et al., 2022). Our previous work demonstrated that continuous vergence tracking responses were significantly reduced with simulated anisometropia of more than 2D for the small targets. This needs to be evaluated with larger natural images for children. In combination with our previous study, these data indicate that both adults and 6-8 year-olds are able to make vergence responses to large step changes in disparity in the presence of defocus up to 2D. Permanent developmental disruption in motor binocular function in the presence of anisometropia is most likely initiated by attempts to maintain binocular fixation and track small changes in disparity.