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Ji He; Thinning of Lens Thickness Might Be Responsible for Myopia Development. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1909.
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© ARVO (1962-2015); The Authors (2016-present)
Recent myopia research suggests that peripheral hyperopia is a risk factor for myopia development and progression, but the sources responsible for the peripheral hyperopic refraction have not been well explored. In a previous modeling (He, ARVO 2010), deepening of anterior chamber depth (ACD) was found to make relative peripheral refraction more hyperopic, and it, therefore, might be a process leading to myopia development. During the eye development, however, ACD deepening is often linked to a thinning process of the lens thickness (LT). The purpose of this study was to theoretically model the effect of LT thinning on relative peripheral refraction.
Ray-tracing on a model eye (Navarro et al. 1985) was performed by using a self-developed MatLab program to calculated Zernike aberrations up to 5th order at eccentricities of visual field across -60 to + 60 deg along the horizontal meridian. LT was assumed to thin from 4.0mm to 3.5mm in three thinning patterns: (1) without any ACD deepening; (2) with ACD deepening and posterior lens surface (PLS) forward moving together; (3) with ACD deepening but no PLS movement.
LT thinning without any ACD deepening (pattern 1) caused relative spherical equivalent error at peripheral field become more myopic. Opposite hyperopic change in relative peripheral refraction was found if the LT thinning was coupled with same amount of ACD deepening (pattern 3). Less hyperopic change was found when the LT was thinned in pattern2. For example, a 0.1mm LT thinning in pattern 1 caused the relative refraction at 40 deg become -0.20D more myopic. But, 0.1mm LT thinning in pattern 3 resulted in 0.18D hyperopic shift at 40 deg. The 0.1mm LT thinning made difference between the two thinning patterns in about 0.38D at 40 deg. Meanwhile, the change in relative peripheral refraction increases with eccentricity, so that 0.1 mm LT thinning produced difference of 0.70D at 60 deg between the two patterns.
The results suggest that effect of LT thinning on relative refraction at peripheral field depends on its thinning pattern. While LT thinning without ACD change could be a protective factor for maintaining emmetropia, LT thinning with ACD deepening might a risk factor for myopia development due to the more hyperopic change in relative peripheral refraction.
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