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Lee M. Johnson, Nancy J. Coletta; Retinal Contours Estimated From Two Optical Methods. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1057.
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Eye shape, or peripheral retinal contour, is a valuable parameter in the study of eye growth during emmetropization and myopia development. Dunne has shown that the contour of the peripheral retina can be estimated from peripheral refractions (Dunne, OPO, 1995). We compared retinal contours calculated from peripheral refractions and Dunne’s algorithm to those measured using partial coherence interferometry in various gaze positions (Mallen and Kashyap, OPO, 2007).
Refractions ranged from -12 D to +6 D in 38 young adult subjects. After pupils were dilated and cyclopleged with 1 gtt 1.0% tropicamide, corneal topography, anterior chamber depth and lens thickness were measured with an Oculus Pentacam and central axial length was measured with a Zeiss IOLMaster. A COAS aberrometer was used to measure refractions across the horizontal and vertical retinal meridians out to 40 deg. Subjects fixated a high contrast letter reflected through a beam splitter mounted between the eye and the COAS; gaze position was adjusted by rotating the beam splitter. Biometry and refractions were used to compute retinal contours with the Dunne scheme. To measure peripheral axial lengths with partial coherence interferometry, a card with fixation marks in various gaze positions was mounted to the IOL Master. Retinal surface coordinates were calculated from the peripheral axial length at each gaze angle by tracing a nodal ray through a three-surface model of each subject’s eye.
Retinal contours calculated from the Dunne and IOLMaster methods were in good agreement. Both methods yielded contours which tended to become more prolate with increasing axial length. In the horizontal meridian, IOLMaster contours tended to be more oblate and slightly displaced anteriorly, with cornea-to-retina distances ranging from 94.3% to 102.7% of the Dunne calculated values (mean 99.2%). Vertical meridian IOLMaster contours ranged in cornea-to-retina distance from 94.2% to 104.8% (mean 101.0%). In the superior retina, IOLMaster contours tended to be slightly more prolate than those calculated from the Dunne model. The IOLMaster contours also showed a faster prolate change with increasing axial length than the Dunne model values.
Partial coherence interferometry is a faster method of estimating retinal contour than peripheral refraction. The measured contours in high myopia are consistent with a prolate eye shape that is asymmetric on the horizontal and vertical meridians, however horizontal meridian contours were less prolate when measured with the IOLMaster than when calculated with Dunne’s algorithm.
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