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S. Diether, C.F. Wildsoet; Compensation for Myopic Defocus under Competing Defocus Conditions in the Chick has Spatial Frequency and Accommodation Prerequisites . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1983.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our recent experimental results suggest that middle to high spatial frequencies are important for the decoding of, and compensation for, myopic defocus. We have since investigated if manipulations of the spatial frequency content of retinal images influence the eye's growth response to competing defocus stimuli. Methods: Lens-cone-devices producing competing defocus of the same amount but opposite sign (+7/-7D) (+40D lens, targets at 33 and 47D) were monocularly applied to 5-day-old chickens for 4 days. At both target positions of the cone, either of two Maltese cross targets were presented (target 1: 1.2 cyc/deg filler pattern, target 2: no filler pattern, spatial contrast: 100% in both cases). In some of the chickens the treated eye underwent ciliary nerve section before attachment of the device. Refractive error (RE) was measured by retinoscopy; vitreous chamber depth (VCD) and choroidal thickness (CHT) were measured twice over the treatment period by high frequency A-scan ultrasonography under anesthesia. Results: With intact accommodation target 1 induced an early hyperopic bias; target 2 by contrast induced a progressively increasing myopic bias (interocular difference means ± SEMs: VCD after 2 days: -0.06±0.03 mm vs. +0.06±0.02 mm; CHT after 2 days: +0.05±0.02 mm vs. –0.03±0.02 mm; RE after 4 days: +0.4±0.7D vs. –2.7±1.0D; significant target effect: p = 0.001, 0.011, 0.022 respectively (repeated measures ANOVA; n = 14, 14)). With paralyzed accommodation both targets induced myopic growth. Target 2, however, produced significantly more myopia than target 1 (VCD after 4 days: +0.46±0.05 mm vs. +0.23±0.06 mm, RE after 4 days: -6.7±1.0D vs. –2.3±0.8D; significant target effect: p = 0.044, 0.012 respectively (repeated measures ANOVA; n = 10, 9)). Conclusions: Our data show that manipulations of the spatial frequency content of retinal images can significantly influence the eye's growth response to competing defocus stimuli. For the eye to distinguish between defocus of opposite sign and appropriately compensate for myopic defocus, there appear to be 2 prerequisites: 1. the retinal image must contain sufficient middle to high spatial frequency information, and 2. accommodation must be intact.
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