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Michael J Collins, Fan Yi, Brett A Davis, Seyed H Hoseini-Yazdi, Hamish McNeill; Rapid changes in the Stiles Crawford Function in response to plus defocus. Invest. Ophthalmol. Vis. Sci. 2020;61(7):548.
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The directionality of the Stiles Crawford Function (SCF) changes following a short-term exposure to a decentred pupillary aperture, potentially through a light guided phototropic mechanism. Since eye growth responds to the vergence of light (emmetropization), the potential for the SCF to change in response to altered light vergence at the retina was examined.
Ten healthy young adults with a mean age (± SD) of 28 ± 6 years participated in three randomly ordered visits, conducted on separate days at the same time of day. The left eye’s SCF was examined (with the right eye occluded) by measuring the relative increment threshold luminance sensitivity of the foveal photoreceptors to a 0.6 degree spot stimulus (conjugate with the natural pupil), located 1.5 mm temporal to the central pupil, before and after a 20-min monocular viewing task performed through a two-channel Maxwellian-view system. The three 20-min viewing tasks included; +1 D optical defocus, optimal correction, or optimal correction viewing images with +1 D simulated blur. Each viewing task was preceded by a 10-min washout period watching a movie through the optical system with optimal correction.
The relative increment threshold luminance sensitivity was 88 ± 7 %, 89 ± 7 % and 89 ± 6 % (for test stimulus at 1.5 mm temporal pupil versus central pupil) at the baseline measurement in the control, +1 D simulated blur and +1 D optical defocus sessions respectively (p > 0.05), consistent with a typical SCF. Repeated measures analysis of variance showed a significant interaction between the condition tested and time (p = 0.028). The relative increment threshold luminance sensitivity increased by 6 ± 4 % during the +1 D optical defocus session, representing a statistically significant change from baseline (p = 0.001). However, the relative threshold luminance sensitivity did not change significantly during the control (1 ± 5 %) and +1 D simulated blur (2 ± 3 %) sessions (both p > 0.05).
Following exposure to plus optical defocus for 20 min, but not to simulated image blur, an increase in threshold increment luminance sensitivity was observed for a test stimulus presented at an off-centre pupil location. This short-term change is consistent with a phototropic mechanism, where the orientation of photoreceptors shifts in response to the altered vergence of the incident retinal light.
This is a 2020 ARVO Annual Meeting abstract.
Two-channel Maxwellian-view system.
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