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J. Tabernero, A. Ohlendorf, M. D. Fischer, U. Schiefer, F. Schaeffel; Classification of Continuous Peripheral Refractive Profiles, Measured With a Scanning Infrared Photoretinoscope in an Adult Population. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2010. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To classify continuous horizontal profiles of peripheral refraction based on different patterns observed in a normal population. To obtain a better understanding of the typical shape of the human retina derived from peripheral refractions.
A continuous scan of the peripheral refraction (±45° every 0.4°) across the vertical pupil meridian of the right eye of 40 subjects (inclusion criterion was a central refraction smaller than ± 2.5 Diopters of spherical equivalent, age range: 18 to 75 years) was performed using a recently developed angular scanning photorefractor. Refractions at different eccentricities in the visual field were fitted using four different mathematical models: 1) "flat" (refraction remains constant across the visual field) 2) "parabolic" variation of refraction as a function of the field. 3) "Linear" change of refraction with eccentricity from the fovea to the periphery and 4) "Square" (or "box") model, with a "flat" central area (no significant changes of refraction as a function of the angle) and a linear change in refraction, starting at a certain peripheral angle. Experimental data was mathematically fitted to each model and, based on the minimal residuals from each fit, each subject was classified as one of the four patterns.
The "square/box" model accurately described the peripheral refraction in 17 out of the 40 subjects. Eight subjects were fitted better with a "linear" model, 5 subjects with the constant "flat" model and 5 with the "parabolic" model. In 5 out of the 40 subjects we could not find a proper classification since they exhibited an irregular profile. About half of the subjects displayed the pattern with no or little variations of the refractions up to an eccentricity of approximately ±15°, and with a subsequent linear change in refraction beyond the edge of this area. Using the Liou-Brennan eye model, it was found that the "square" model would apply to subjects with a retina with a local curvature that decreases (becomes "flatter") in the central "plano" area and begins to increase at the edge of it, inducing a linear change in refraction towards hyperopia.
The majority of the peripheral refraction profiles in an adult population (35 out of 40 subjects) classified according to four different established mathematical models of variation with eccentricity. Future studies might establish a relationship of each model with the central refractive errors, or their progression.
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