Accommodation modulates the individual difference between objective and subjective measures of the final convergence...

Area of Science:

• Vision Science
• Ophthalmology
• Neuroscience

Background:

• Subjective vergence overestimation (SVO) is a common issue in measuring vergence eye movements using dichoptic nonius lines.
• This overestimation arises from coupled vergence and accommodation demands during step responses, known as 'forced vergence'.

Purpose of the Study:

• To investigate methods for reducing SVO by decoupling vergence and accommodation.
• To compare subjective vergence measurements with objective recordings under varying stimulus conditions.

Main Methods:

• Utilized a mirror-stereoscope to present disparity step stimuli and measure convergence responses.
• Employed nonius lines for subjective vergence estimation and an EyeLink II system for objective recordings.
• Tested stimuli including a vertical line, cross/rectangle, and difference-of-Gaussians (DOG) pattern with step sizes of 180 and 60 min arc.

Main Results:

• For 180 min arc steps, subjective measures overestimated objective vergence, with SVO being 20 min arc for the line and 12 min arc for the DOG pattern.
• No SVO was observed for 60 min arc step responses.
• Accommodation changes correlated with SVO (r = 0.77), indicating reduced conflict with the DOG pattern and smaller steps.

Conclusions:

• Decoupling vergence and accommodation demands, particularly with stimuli like the DOG pattern or for smaller steps, reduces SVO.
• Minimized conflicting sensory demands lead to better agreement between subjective and objective vergence measurements.
• Findings suggest strategies to improve the accuracy of subjective vergence eye movement assessments.