Abstract
Purpose: :
To determine whether the 40cm ranges of clear and single binocular vision (CSBV) derived from phoropter prism vergence tests would match the ranges of CSBV measured in a stereoscopic 3D display, and to determine whether vergence rate affected the limits of CSBV in the 3D display.
Methods: :
47 binocular young adults underwent routine clinical divergence (BI) & convergence (BO) phoropter prism vergence tests of their CSBV limits at 40cm. In separate sessions the same subjects underwent jump vergence and smooth vergence tests of their CSBV disparity limits in an electronic mirror haploscope (i.e., stereoscopic 3D display). Target disparity was limited to ±35 prism diopters (pd) by the 17.5cmx12.5cm display, viewed at a 15pd (40cm) distance. The target was a maltese cross, 1cm W x 3cm H at 40cm. Its visual angle changed congruently with target disparity. Smooth vergence target disparity changed at rates of 0.5, 1, 2, or 4 pd/sec.
Results: :
Our mean phoropter BI and BO smooth vergence blur and break values were similar to those reported in previous studies. The mean BI limit of CSBV at 2pd/sec was less in the 3D display (9.76pd) than in the phoropter (12.49pd) (paired t-test, t=3.43, p=0.0013). Most BO ranges of CSBV at 2pd/sec were greater in the 3D display than in the phoropter, reaching the 35pd limit of the 3D display in 24 subjects. In contrast, the mean BO limit of CSBV in the phoropter was 19.26pd, and only 4 subjects maintained CSBV to 35pd BO in the phoropter (sign test, z=4.57, p=7.6E-5). The BI limits of CSBV in the 3D display increased with smooth vergence rate from 7.38pd at 0.5Hz to 11.33pd at 4pd/sec (One-way ANOVA, F=12.71, p=2.38E-9). The mean CSBV limit for BI jump vergence, 5.11pd, was smaller than the smooth vergence CSBV limits at all rates. The effect of vergence rate on the BO range of CSBV could not be evaluated because 21 subjects exceeded the convergence disparity limits of the 3D display at all 4 rates. The mean BO jump vergence limit of CSBV, 8.7pd, was noticeably less than all mean BO smooth vergence CSBV limits.
Conclusions: :
The range of CSBV derived from phoropter vergence tests was not a good approximation of the range of CSBV obtained from our 3D stereoscopic display. Vergence rate seems to be one factor controlling CSBV range in our 3D display, at least in divergence.
Keywords: eye movements • vergence • binocular vision/stereopsis