No abstract

Although different optometric tests of accommodation and vergence rely on the same basic principles, the results of this study indicate that clinical and laboratory methods actually involve distinct components. These differences, which are induced by methodological choices, must be taken into account, when comparing studies or when selecting a test to investigate a particular oculomotor component.

Citation: Neveu P, Roumes C, Philippe M, Fuchs P, Priot A-E. Stereoscopic viewing can induce changes in the CA/C ratio. Invest Ophthalmol Vis Sci. 2016;57:4321-4326. DOI:10.1167/ iovs.15-18854 PURPOSE. Stereoscopic displays challenge the neural cross-coupling between accommodation and vergence by inducing a constant accommodative demand and a varying vergence demand. Stereoscopic viewing calls for a decrease in the gain of vergence accommodation, which is the accommodation caused by vergence, quantified by using the convergenceaccommodation to convergence (CA/C) ratio. However, its adaptability is still a subject of debate.METHODS. Cross-coupling (CA/C and AC/A ratios) and tonic components of vergence and accommodation were assessed in 12 participants (27.5 6 5 years, stereoacuity better than 60 arc seconds, 6/6 acuity with corrected refractive error) before and after a 20-minute exposure to stereoscopic viewing. During stimulation, vergence demand oscillated from 1 to 3 meter angles along a virtual sagittal line in sinusoidal movements, while accommodative demand was fixed at 1.5 diopters. RESULTS.Results showed a decreased CA/C ratio (À10.36%, df ¼ 10, t ¼ 2.835, P ¼ 0.018), with no change in the AC/A ratio (P ¼ 0.090), tonic vergence (P ¼ 0.708), and tonic accommodation (P ¼ 0.493).CONCLUSIONS. These findings demonstrated that the CA/C ratio can exhibit adaptive adjustments. The observed nature and amount of the oculomotor modification failed to compensate for the stereoscopic constraint.Keywords: accommodation, vergence, CA/C, stereoscopic viewing A ccommodation and vergence are neurologically crosscoupled and interact dynamically, so that an accommodative stimulus induces both accommodative and vergence responses-and vice versa for a vergence stimulus. The vergence evoked by accommodation, known as accommodative vergence, can be quantified by using the AC/A ratio, which assesses the amount of vergence per unit change in accommodation. The accommodation induced by vergence, known as vergence accommodation, can be quantified by using the CA/C ratio, which measures the amount of accommodation per unit change in vergence. Different static and dynamic models of the accommodative and vergence systems have been proposed to provide an understanding of the organization and the interaction between the two systems.

No abstract

Oculomotor conflict induced between the accommodative and vergence components in stereoscopic displays represents an unnatural viewing condition. There is now some evidence that stereoscopic viewing may induce discomfort and changes in oculomotor parameters. The present study sought to measure oculomotor performance during stereoscopic viewing. Using a 3D stereo setup and an eye-tracker, vergence responses were measured during 20-min exposure to a virtual visual target oscillating in depth, which participants had to track. The results showed a significant decline in the amplitude of the in-depth oscillatory vergence response over time. We propose that eye-tracking provides a useful tool to objectively assess the timevarying alterations of the vergence system when using stereoscopic displays.