Diurnal variations in keratometry and refraction with intracorneal ring segments

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Abstract
To study refraction variations during the day in eyes with intrastromal corneal ring segments (ICRS) to correct low myopia. Monticelli Clinic, Marseille, France. Thirteen eyes with ICRS were included in the study; the ICRS was explanted from 3 eyes because of undercorrection. The minimum follow-up in all eyes was 1 year. The same observer measured refraction and keratometry at 9:00 AM, 1:00 PM, and 7:00 PM with the same autokeratorefractometer. To validate the analysis method, these eyes were compared with a group of emmetropic control eyes that had not had surgery and with a group of eyes that had photorefractive keratectomy for a similar degree of myopia. All measurements were done under the same conditions. After 1 year, the ICRS eyes showed a tendency toward an evening myopic shift. This was confirmed by the objective keratometry study, which showed variations closely correlated with the myopia observed. These phenomena were not observed in the other groups. The ICRS had satisfactory predictability in eyes with up to -3.50 diopters of myopia. However, the evening myopic shift appeared similar to that observed after radial keratotomy.