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Ge Chen, Zhong-Lin Lu, Chang-Bing Huang; Quantify Functional Impairments in Myopic Vision. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3004.
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© ARVO (1962-2015); The Authors (2016-present)
Myopia results in degraded visual functions if uncorrected. Although it is generally acknowledged that myopia attenuates high spatial frequency information, little is known about the exact functional impairments in myopic vision. Here, we measured contrast sensitivity functions in several external noise levels in corrected and uncorrected myopic vision, and applied the perceptual template model (Lu & Dosher, 2008) to quantify functional impairments in myopia.
The method of constant stimuli was used to measure the psychometric function for detecting a sine-wave grating in a 2AFC task in three spatial frequencies, three external noise levels, and two refractive status (corrected or uncorrected) conditions. Each psychometric function was sampled at five contrast levels, leading to 90 conditions in total. The perceptual template model was fit to the data to evaluate how the various sources of observer inefficiency varied with spatial frequency and refractive status.
The model that allows internal additive noise and template gain changed significantly with spatial frequency accounted for 92% of data variance. Specifically, the internal additive noise was higher without than with optical correction. On the other hand, the template gain was slightly higher at low spatial frequencies but lower at higher spatial frequencies without optical correction as opposed to optical correction. With optical correction, contrast sensitivity at zero external noise only correlated with internal additive noise (R^2=0.62, p<0.05) and contrast sensitivity in high external noise only correlated with the template gain (R^2=0.77, p<0.01). Unexpectedly, we found contrast sensitivity, if tested without correction, was jointly determined by internal additive noise and template gain in both zero and high external noise conditions without optical correction, the results were drastically different (all R^2>0.60, p<0.05).
Our results indicated that long-term myopic experience may have reshaped the visual system. Contributions of optical and neural processing to the two refractive conditions will be discussed. The results are potentially important for understanding myopic vision deficits, and the development of rehabilitation methods to restore spatial vision in myopia.
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