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J. Tabernero, F. Schaeffel; Continuous Peripheral Refraction Profiles Measured With a Scanning Infrared Photoretinoscope in Myopic and Emmetropic Students. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3944.
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To present a new method for continuous measurements of refractive state as a function of the angle of eccentricity. To improve the description of the peripheral eye shape in myopes and emmetropes using this new instrument.
We designed a scanning photorefractor to record refractive errors in the vertical pupil meridian across the horizontal visual field (until ± 45º). The set-up consists of a hot mirror that continuously projects the infrared light from a photoretinoscope under different angles of eccentricity into the eye. The movement requires at least two mechanical degrees of freedom (translational and rotational) which was achieved by using two independently controlled stepping motors. The motors were controlled via the USB port of a PC by custom written software in Visual C++. The software was implemented into previously developed programs for automated photoretinoscopy. A group of 17 emmetropic subjects and 11 myopic subjects (mean -4.3 D, standard deviation 1.7 D) were measured without spectacle corrections. For analysis of eye shapes, the refractive error versus the eccentricity angles were fitted with different polynomials from second to tenth order. The errors of every fit were described in terms of standard error of the estimate in Diopters.
The new set-up presents some important advantages over previous techniques: the detection of the Purkinje image for gaze tracking is no longer needed since the angles are determined by the position of the hot mirror, the subject does not have to change gaze during the measurements and a continuous profile is obtained rather than discrete points. The analysis of the data also revealed new results. There was a significant difference in the fitting errors between myopes and emmetropes. Tenth order polynomials were required in myopes to achieve similar quality of fit, as in emmetropes fitted with only fifth order polynomials. Apparently, the peripheral shape of the myopic eyes is more "bumpy".
A new set-up is presented to measure continuous peripheral refraction profiles. It was found that the peripheral retinal shape is more "bumpy" even in only moderately myopic eyes.
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