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The purpose of this study was to investigate how sustained convergence induces phoria adaptation and changes divergence dynamics.

Near dissociated phoria and divergence step responses were recorded using an infrared eye movement monitor on four binocularly normal subjects. We tested three different adapting vergence positions (16°, 6°, and 0.5°) and measured 4° divergence step responses for two different initial vergence positions (16° and 4.5°). Dynamics were quantified by measuring peak velocities of the divergence responses.

Phoria was significantly adapted after subjects fixated on a sustained convergent target at near (16°) and at far (0.5°). As a result of sustained convergence, divergence peak velocity from a 4° step stimulus significantly changed. A regression analysis showed that when the phoria became more esophoric (near adapted) the peak velocity for …