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Timothy G Shepard, Christopher Patrick Taylor, Frances J Rucker, Rhea T Eskew; Sensitivity to Incremental S-cone Stimuli and the Development of Myopia. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5523.
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© ARVO (1962-2015); The Authors (2016-present)
One source of information that is available to the developmental emmetropization mechanism comes from longitudinal chromatic aberration (LCA). With hyperopic defocus (a shorter eye), contrast will be higher for short wavelength components of an image, while with myopic defocus (longer eye), contrast will be higher for long wavelength components. In terms of an emmetropization mechanism, a child who is more sensitive to short-wavelength (S) cone signals is more likely to keep short-wavelengths in focus. S-ON retinal ganglion cells would be more excited by increasing S cone contrast, potentially providing a signal that could be used to slow eye growth by driving the plane of focus towards shorter wavelengths. (S-OFF cells would be excited by decreasing S cone contrast and would potentially drive the plane of focus towards the longer wavelengths, but this signal may be redundant with signals provided by the L and M wavelength cones). Reduced sensitivity to S increment (S+) stimuli may therefore be associated with the development of myopia; if this sensitivity difference persists across the lifespan, there should be a relationship between S+ sensitivity and refraction in adults.
A 2AFC, adaptive staircase procedure was used to measure detection thresholds to a 3cpd Gabor patch which modulated along four different directions in cone contrast space—achromatic and the three cone isolating directions (L, M, and S), all of which contain both incremental and decremental contrasts. In addition, a Gaussian Blob, with σ=2°, was used to test S+ (purplish) and S- (yellow/green) stimuli separately. A total of 29, mostly unpracticed adult participants, all of whom had normal Rayleigh match scores, were refracted, and were corrected using a trial lens placed in front of the dominant eye; the other eye was patched. Almost all participants had corrections within ±3 diopters.
There was no significant linear relationship between refraction (best sphere) and any of the bipolar Gabor stimuli (achromatic, L cone, M cone, or S cone). However, there was a significant linear relationship between refraction and the S+ threshold (r=-0.52 p < 0.05): myopes were less sensitive to S cone increments.
This exploratory study supports the hypothesis that myopes are less sensitive to incremental S cone stimuli than emmetropes or (mild) hyperopes.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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