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  • Title: Stereoscopic Viewing Can Induce Changes in the CA/C Ratio.
    Author: Neveu P, Roumes C, Philippe M, Fuchs P, Priot AE.
    Journal: Invest Ophthalmol Vis Sci; 2016 Aug 01; 57(10):4321-6. PubMed ID: 27552410.
    Abstract:
    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 convergence-accommodation 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 ± 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 (-10.36%, df = 10, t = 2.835, P = 0.018), with no change in the AC/A ratio (P = 0.090), tonic vergence (P = 0.708), and tonic accommodation (P = 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.
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