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D. Y. Tse, J. W. Chan, C.-H. To; Effect of Spatial Angle on Emmetropization Under Competing Defocus Condition. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3587. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The visual scene comprises of multiple defocus which may be described by sign, magnitude, solid angle and eccentricity. While previous studies have suggested the potential role of peripheral defocus on axial emmetropization, it is unclear whether the effect of peripheral defocus is dependent on the solid angle subtended. We sought to investigate this by varying spatial ratio between competing defocus on emmetropization under a controlled viewing environment.
A dual-plane lens-cone system was modified from earlier studies. The two planes containing the visual targets were positioned at dioptric distances of 45D and 25D. A clear PMMA lens of back vertex power of +35D was embedded inside the cone to simultaneously provide opposite defocus of +10D and -10D. Grating patterns of 1 cycle/deg were printed on the two planes. To vary the relative contribution from the opposite defocus in terms of spatial angle, the near plane was constructed by interleaving grating patterns with numerous hexagon-shaped transparent areas where the distant plane came under viewing. Spatial ratios (+10D: -10D) tested were 50:50, 40:60, 33:75, 25:75. They were compared with single defocus and open-viewing controls. The lens-cone system was applied unilaterally with Velcro. Field of vision provided was 60-70 degree. The fellow eye acted as a control. Refractive error and ocular dimensions were measured along the axis by retinoscopy and A-scan ultrasonography respectively under isofluorane anaesthesia before the treatment, and at the third and sixth day after treatment.
Interocular refractive errors (D, Mean± SEM) at day 6 were: 10.4±0.9D, 7.6±1.4D, 5.9±1.3D, 1.6±1.0D, -2.4±1.0D and -8.9±1.0D for spatial ratios of 100:0, 50:50, 40:60. 33:67, 25:75 and 0:100 respectively.Interocular vitreous chamber depths (µm, Mean± SEM) at day 6 were: -515±51, -447±52, -253±78, -105±95, 230±77 and 592±61 for spatial ratios of 100:0, 50:50, 40:60. 33:67, 25:75 and 0:100 respectively.Refractive error and vitreous chamber depth for the 33:67 and 25:75 groups were intermediates and were significantly different from that of the single defocus controls at the 0.05 level (n=7-8).
Our data has showed that, under competing defocus condition, the emmetropization set-point varied with the spatial angle subtended by the defocus. These findings further suggest that an integrative process or summation of multiple spatial defocus in the visual scene may be employed in the decoding of visual stimuli for emmetropization.
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