Peripheral retinal shape measurements, using the IOLMaster, in myopia and hyperopia

Abstract

Purpose: When measuring peripheral retinal shape using the IOLMaster, measurements have been taken with the instrument in a fixed position and the subjects rotating their eye to measure peripherally. However, eye rotation could affect the peripheral ocular shape measures. The aim of this experiment is to determine the effect of eye rotation upon the measurement of peripheral retinal shape in myopic and hyperopic subjects using the IOLMaster.Methods: 20 subjects participated with informed consent in the experiment [10 myopes (MYO) and 10 hyperopes (HYP)]. All subjects were visually normal with visual acuity of 0.0 logMAR or better. The mean age of the subjects was 21.4 ± 2.2 years, and all were students in the University. Cycloplegia and mydriasis were induced using 1.0% cyclopentolate and the measurements were taken 30 min after instillation of the eyedrops. Peripheral retinal dimensions were measured with the IOLMaster (Carl Zeiss Ltd., Welwyn Garden City, UK) which measures axial length using partial coherence interferometry. 5 measures of axial length were taken at 10 degree intervals from 0–40 degree nasally and temporally using two different experimental paradigms. Experiment 1: Subjects rotated their eye to view an LED target array, attached to the front of the instrument. Experiment 2: Subjects maintained fixation upon a stationary target in the primary position while the IOL‐Master was rotated about the centre of rotation of the eye. The data was fitted with second order polynomials with separate curves being fitted to the temporal and nasal profiles to take into account any retinal asymmetry.Results: A significant difference (p < 0.01) was found in the mean second order coefficients for the temporal and nasal retinal profiles in the MYO subjects, with the temporal retina having the lower coefficient. There was no significant difference between temporal and nasal second order coefficients in the HYP subjects. Eye rotation produced a significant shift in the second order coefficients for both temporal (p < 0.01) and nasal (p < 0.01) retinal profiles in the MYO group, with the coefficients becoming smaller with ocular rotation. No significant effect of eye rotation was found in the HYP group.Conclusions: Asymmetry between the temporal and nasal retinal profiles is more pronounced in the myopic eye. Ocular rotation has a substantial and measurable effect on the shape of the myopic eye, but no measurable effect is found in the hyperopic eye. These results are indicative of substantial structural differences between the eyes of subjects with myopia and hyperopia. When measuring peripheral retinal shape these factors should be taken into account.