Abstract
Purpose :
Time spent outdoor is a key parameter to prevent the onset of myopia. The purpose of this study is to examine whether monocular vergence and visual image contrast may suffice to drive emmetropization when comparing indoor with outdoor vision.
Methods :
Vision has been examined with computational raytracing for both foveal and parafoveal vision (using ComsolTM) for foveal and parafoveal vision with realistic cone densities of 160,000/mm2 to 7,000/mm2 and appropriate visual pigment densities representative of the S, M, and L cone populations in a simplified eye model. The computational method builds on the volumetric overlap model between light and photoreceptors (Vohnsen et al, J. Vision 2017) weighted with the absorption coefficients of outer segments. Monocular vergence and visual image contrast has been computed for an outdoor 2mm pupil and an indoor 4mm pupil.
Results :
The results show that large monocular vergence, even in the absence of aberrations, will cause image degradation that may confound the emmetropization process. This holds true for both foveal and parafoveal vision. In turn, smaller vergence from a 2mm pupil reduces blur and increases visual image contrast. With larger eye pupil the only optical mechanism that reduces blur is by promoting eye growth both axially and peripherally. A doubling of the pupil size reduces computed visual contrast by up to 50% although this will be dampened by the Stiles-Crawford effect of the cone photoreceptors (Carmichael Martins and Vohnsen, Biomed. Opt. Express 2019). Thus, optical vergence, rather than a lack of light exposure per se, may trigger the onset of myopia.
Conclusions :
The 3-D structure of the retina is central to a full understanding of light absorption and vision. The results found from eye modeling with realistic cone photoreceptor and pigment densities show that large monocular optical vergence may promote undesired eye growth.
This is a 2020 ARVO Annual Meeting abstract.