Diurnal variations in keratometry and refraction with intracorneal ring segments

PURPOSE

To study refraction variations during the day in eyes with intrastromal corneal ring segments (ICRS) to correct low myopia.

SETTING

Monticelli Clinic, Marseille, France.

METHODS

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.

RESULTS

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.

CONCLUSION

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.

[Diurnal variations of refraction and keratometry after intracorneal rings]

Within a European evaluation, we participated in the study of ICRS on low myopia. During the period of observation, subjective refraction variations in the day were underlined. This phenomenon remains to be specified.

MATERIAL AND METHODS

Thirteen eyes were included in the study, 3 were explanted because of under-correction. The minimum follow-up is one year for all eyes. The same observer measured refraction and keratometry in all eyes on the same day at 9:00 am, 1:00 p.m. and 7:00 p.m., with the same automatic autokeratorefractometer. To validate the analysis method, these patients were compared with a group of emmetropic control eyes never operated on and with a group of eyes operated on with a PRK for similar myopia. All measurements were done under the same conditions.

RESULTS

After one year, a tendency to evening myopisation was noticed in ICRS eyes and confirmed by the objective keratometry study showing variations closely correlated with the myopia observed. These phenomena were not observed in the two other groups.

DISCUSSION

The examination technique was validated by the absence of variation observed on normal eyes. The tendency to diurnal myopisation is rather constant on the whole population studied with a more or less important degree from patient to patient. These observations never reported in the literature, deserve to be confirmed on other sites.

CONCLUSION

In this study ICRS allowed to correct low myopia with a satisfactory predictability up to -3.50 D. However, the appearance of an evening myopisation recalls that observed after radial keratotomy. Complementary studies are necessary to explain the intimate mechanism of this phenomenon.