Optical and topographic changes in keratoconus after implantation of Ferrara intracorneal ring segments.

PURPOSE: To assess the morphological, optical, and visual properties of the cornea before and after implantation of Ferrara intracorneal ring segments (ICRS) and compare them to normal values.

METHODS

Thirty-seven keratoconic eyes were implanted with Ferrara ICRS and compared pre- and postoperatively with 38 non-keratoconic (normal) eyes. Examinations were performed using the NIDEK Optical Path Difference (OPD)-Scan II and analyzed using OPD-Station software. Keratometric data were assessed, in addition to OPD, Zernike coefficients, point spread function (PSF), and modulation transfer function (MTF).

RESULTS

Considering correlations, the central 3 mm cornea was found responsible for the low quality vision in keratoconus (P<.01). After implantation of Ferrara ICRS, all keratometric parameters improved significantly. Optical path difference also improved. Except for tilt and other lower order Zernike coefficients, higher order aberrations, PSF, and MTF did not change. The effect of flattening is greater at the central 3 mm, but the para-central changes are responsible for the residual defects (ie, incomplete improvements of high optical and visual functions).

CONCLUSIONS

Ferrara ICRS improve topographic and visual results in keratoconic eyes.