Wavefront aberrations associated with the Ferrara intrastromal corneal ring in a keratoconic eye

To describe the optical implications of the aberration pattern of a keratoconic eye implanted with an intrastromal corneal ring (Ferrara ring).

A 32-year-old man with bilateral keratoconus had a Ferrara intrastromal corneal ring implanted in his right eye. Surgery was uneventful and both uncorrected (UCVA) and best spectacle-corrected (BSCVA) visual acuity improved. Corneal topography was performed before and after surgery. Wavefront measurements were performed 1 month after the procedure in both eyes for comparison. The point spread function, modulation transfer function (MTF), and convolved acuity chart were analyzed.

The right eye--implanted with the intrastromal Ferrara ring--had high root-mean-square (RMS) values for higher order aberrations. The left eye-keratoconus without an intrastromal ring-had moderate values. Point spread function, MTF, and convolution acuity charts are presented for each eye, with the latter two showing improved visual function in the implanted eye, despite a higher aberration value.

The wavefront measurement device captured aberrations even in a highly aberrated eye. Despite better UCVA and BSCVA, the Ferrara ring notably increased higher order aberrations compared to the fellow eye, but with a more uniform central pattern. In this case, the larger RMS value was a poor predictor of good visual function; other metrics better predicted the patient's subjective response. Metrics other than RMS error may be necessary to better correlate aberration value with visual satisfaction in some eyes.