Abstract
Purpose :
Vergence is the disjunctive eye movement used to track objects varying in depth. Current tests involve symmetric binocular disparity vergence measurements where the visual stimulus appears centrally. We developed a novel testing paradigm where an asymmetric visual stimulus moves towards and away from the left or right eye while simultaneously eliciting convergence or divergence. We aim to characterize inter-individual, differential pupillary responses between symmetric and asymmetric vergence tasks and ascertain the suitability of these tasks to identify oculomotor abnormalities in the mTBI population.
Methods :
Healthy volunteers (n=3) underwent calibration with the Neurolign Dx100™ (Neurolign USA LLC, Pittsburgh PA) device prior to experimental vergence tasks. The Dx100™ presented a sinusoidal binocular disparity visual fixation target (red dot in the center of the letter “X”) via central (TCVP), left (TLVP), and right-sided (TRVP) targets moving at 0.10 Hz for symmetric and asymmetric vergence pursuit tasks. Central, left, and right sided vergence steps tasks (TCVS, TLVS, and TRVS, respectively) were administered at 5° every 1.5s for 3 cycles total. Pupil area and eye position were recorded continuously. Generalized linear models were constructed to model pupil diameter based on interactions between visual stimulus, time, and horizontal positions of both eyes.
Results :
Gain and total excursion were symmetric in all participants following TCVP (Table 1). There was an average gain of 1.87 in the right eye during TLVP and 1.77 in the left eye during TRVP. Gain was minimal in the contralateral eye during asymmetric tasks, though grand mean pupil diameter was similar across all tasks regardless of stimulus position. TCVS inward and outward amplitudes were symmetric. During TLVS, left eye inward and outward amplitudes were a mean of 4.60 and 4.53 with minimal movement in the right eye. In TRVS, the right eye inward and outward amplitudes were 4.64 and 4.03 with minimal movement in the left eye (0.21, 1.46, respectively). Goodness of fit (R2) was similar between models, regardless of stimulus position or vergence task.
Conclusions :
Asymmetric vergence targets elicit consistent, differential pupillary responses in healthy individuals, providing a critical foundation for developing sensitive, specific quantitative tests for evaluation of vergence dysfunction.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.