Optical quality of the cornea one year after Cretan protocol plus in eyes with keratoconus

Cretan protocol plus is a novel technique that combines corneal cross-linking with refractive procedures in patients with keratoconus. Visual improvement is not only limited to visual acuity, the optical quality may also be enhanced by the Cretan protocol.

To evaluate the higher-order aberrations (HOAs) and optical quality of the cornea 1 year after the Cretan protocol plus in keratoconus patients.

The uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refraction spherical equivalent (MRSE), and topographical analysis of the cornea were assessed. The corneal optical quality parameters, including total HOA (Z_3-8), vertical coma (Z₃^-1), horizontal coma (Z₃¹), vertical trefoil (Z₃^-3), oblique trefoil (Z₃³), and spherical aberration (Z₄⁰), modulation transfer function (MTF) and Strehl ratio of point spread function (PSF) over the 4 mm diameter pupil were recorded via Sirius dual-scanning corneal tomography. All data were analysed preoperatively, 1 month, 6 months, and 1 year postoperatively.

Twenty eyes of 16 keratoconus patients with 1 year of follow-up were included. After the Cretan protocol plus, the mean UDVA, CDVA, MRSE, corneal astigmatism, simulated keratometry-1, simulated keratometry-2, and maximum keratometry (Kmax) improved significantly throughout the follow-up visits (p < 0.001). Total HOA, vertical coma, and spherical aberration were significantly reduced at 1 year compared with the preoperative values (p < 0.05). Vertical coma was decreased from preoperative to all postoperative time points (p = 0.009). Regarding optical quality, MTF 5 and MTF 10 at both the vertical and horizontal meridians were significantly increased 1 year after the Cretan protocol plus compared to preoperatively (p < 0.05). Significant improvements in the PSF occurred at all postoperative time points (p < 0.001).

The Cretan protocol plus is more efficient in improving optical quality while reducing corneal aberrations in keratoconus patients. Vertical coma and PSF could be objective indicators of optical performance after this procedure.