Heath components of objective accommodative responses for convergence insufficiency participants compared with those with binocularly normal vision

SIGNIFICANCE: Understanding the deficits in accommodative responses in convergence insufficiency compared with binocularly normal vision participants can guide targeted therapies to improve accommodative function. PURPOSE: The first objective is to evaluate the Heath components (defined as blur, disparity, and proximal cues that elicit accommodative responses) in convergence insufficiency participants. This is achieved by analyzing objective accommodative responses to step stimuli, assessing the pre-programmed and feedback mechanisms through peak velocity and final amplitude, respectively. The second objective is to compare these pre-programmed and feedback components of the accommodative system between participants with convergence insufficiency and those with normal binocular vision. METHODS: Accommodative responses to isolated and combinatory Heath visual cues were assessed in 28 convergence insufficiency participants and 31 binocular normal vision participants. Blur, disparity, and proximal cues, stimulated in isolation, paired, or all three, lead to seven movement types. The peak velocity and final amplitude of each response were measured for each movement and participant. Comparison among the seven movement response types for the convergence insufficiency group was assessed using one-way analysis of variances. Linear Mixed Models assessed the main interaction of participant type by visual cue effects, and post-hoc tests evaluated pairwise differences. RESULTS: When assessing the Heath components of the convergence insufficiency group, significant differences were observed for peak velocity and final amplitude in focus and defocus responses for the cue combinations (p<0.001). When blur and disparity were stimulated, the final amplitude reached the intended target. When blur or disparity were stimulated, there was a significant reduction in final amplitude and peak velocity compared with responses when blur and disparity were both presented. The proximal-only responses had the slowest peak velocity and reduced final amplitude compared with the other response types. Significant differences were observed in peak velocity and final amplitude for focus and defocus responses between the convergence insufficiency and normal binocular vision groups for certain visual cues (p<0.02). CONCLUSIONS: The accommodative responses of the convergence insufficiency group were more accurate when both blur and disparity were present, compared with other visual stimulus combinations. The convergence insufficiency and binocular normal vision groups were significantly different for the blur and disparity cues.