The intrastromal corneal ring in clinical refractive surgery: reference to results in rabbit eyes

The intrastromal corneal ring (ISR) is a refractive device recently introduced for clinical application that is implanted in the mid-peripheral corneal stroma in order to correct myopia without invasion of the central optical zone. First clinical results of intracorneal ring segment implantation were published recently. These results reveal striking similarities to our own experimental data, only briefly published up to now. The aim of this study is to present the refractive and histopathological data of ISR implants in rabbits and to compare these results with the clinical data actually available.

Expansion/constriction effects were evaluated with a ring of constant size (7.5 x 0.5 x 0.2 mm) in channels of 7.0, 7.5, or 8.0 mm in diameter, volume effects by implantation of 7.5-mm rings with varying thickness (0.2, 0.3, 0.4 mm) into a channel of 7.5 mm, respectively. Refractive power was measured preoperatively and at day (D) 7, D14, D30 for the first and the second experiment, plus D60, D90 for the second experiment. Histological evaluations of the induced morphological changes were additionally performed at all time intervals.

Significant (P<0.05) flattening of the cornea was obtained in all but the first (constant ring, 7.0-mm channel) implants postoperatively at D7 and/or D14, with mean dioptric changes up to -5.03+/-2.92 compared with controls. However, from D30 on, there was no statistically significant difference between operated and control eyes. Biomicroscopy and histology of the implanted eyes revealed good biocompatibility, with only rare major complications such as stromal abscess or massive neovascularization.

Although our implantation technique differs slightly from that employed in the recent FDA studies, our results tend to confirm the maximal achievable refractive change of about -5 dpt with this procedure. Furthermore, this study is the first to demonstrate that in rabbits, ISR implantation has only a shortterm effect on refractive power. Our results indicate that long-term refractive follow-up may be necessary in human eyes prior to the introduction of ISRs as a routine procedure in refractive surgery.