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Y. Liu, J. Hsieh, C. F. Wildsoet; A Study of the Repeatability of Peripheral Refraction Measurements and the Effects of Orthokeratology (OrthoK) Contact Lens Wear. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2604.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the reliability of cycloplegic peripheral refraction measurements using Grand Seiko WR-5100K autorefractor and the effect of OrthoK lens wear on peripheral refractions. Speculation that peripheral refractive errors underlie myopia development and progression motivated this study.
Peripheral refractive errors were measured at 5-degree intervals out to 35 degrees eccentricity using Grand Seiko WR-5100K autorefractor with an add-on red LED fixation bar at 50cm. Both eyes of 27 young adult subjects (mean age: 24.3yr; mean RE: -3.39Â±1.08D) were measured under very low room illumination, 20 minutes after instillation of a combination of 1% proparacaine, 2.5% phenylephrine, and 0.5% tropicamide. For each subject, baseline data were obtained within 1 week prior to the start of the OrthoK treatment, a 2nd set of data being collected approximately 1 month later, after vision had stabilized with overnight wear of OrthoK contact lenses. Refractions were converted to vector form; derived mean sphere (M), 90Â° to 180Â° astigmatism (J180), and 45Â° to 135Â° (J45) were then subject to multivariable regression (y=ax2+bx+c; critical p-value of 0.05), paired t-test and descriptive analyses with OrthoK treatment as the major explanatory variable, adjusting for baseline central refraction, baseline corneal asphericity, within-subject correlation, and inter-ocular variability.
Prior to OrthoK treatment, subjects showed either little change in mean sphere refraction with eccentricity or relative hyperopia compared to their central refraction. The OrthoK treatment decreased significantly myopic errors within Â±10Â° (M: -0.06 Â±0.43, 0Â°), but caused significant relative myopic shifts in the Â±10-30Â° zone (e.g., M shift: -1.73 Â±1.44D, 20Â°), with relatively little change beyond Â±30Â° of eccentricity (e.g., M shift: -0.49 Â±1.52D, 35Â°). The M and J45 components showed good repeatability at all eccentricities while the repeatability of the J180 component decreased significantly beyond Â±30Â° after OrthoK treatment, presumably due to the high irregularity of the cornea in this transition zone.
The Grand Seiko WR-5100K autorefractor with add-on fixation bar allows reliable measurement of peripheral refractive errors out to 30Â° eccentricity in OrthoK-treated subjects. If peripheral relative hyperopia is a risk factor for the progression of myopia, as speculated by others, then OrthoK is a plausible myopia control treatment, given that they are significantly reduced by this treatment.
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