Faculty Bibliography

PURPOSE:To compare higher order aberrations (HOAs) in normal eyes between a Scheimpflug imaging system (Pentacam HR) and dual Scheimpflug-Placido imaging system (Galilei G4). SETTING:Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, USA. DESIGN:Retrospective case series. METHODS:Eyes screened for refractive surgery were evaluated sequentially using a Scheimpflug device and a dual Scheimpflug-Placido device. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated. RESULTS:One hundred five eyes of 105 patients (44 men, 61 women) were evaluated. Total RMS, coma, and trefoil were significantly different between groups (all P < .001), while spherical aberration values were not. There was moderate correlation between devices for trefoil (r = 0.475 to 0.652), coma (r = 0.574 to 0.651), and spherical aberration (r = 0.483) and a strong correlation for total cornea RMS (r = 0.817). There was no directional bias between groups. The 95% limits of agreement for absolute values was 0.039 μm for trefoil at 30 degrees, 0.405 μm for trefoil at 0 degree, 0.553 μm for horizontal coma, 0.545 μm for vertical coma, 0.318 μm for spherical aberration, and 0.617 μm for RMS. CONCLUSIONS:A Scheimpflug imaging device and dual Scheimpflug-Placido imaging device generated statistically different values for total cornea HOAs; however, the correlation between devices was moderate to strong and there was reasonable agreement in all measures for normal eyes. Based on these findings, the devices appear functionally equivalent for clinical use, although caution is warranted for outcomes-based research protocols that report HOAs.

PURPOSE/OBJECTIVE:To compare the relative 12-month corneal crosslinking (CXL) functional outcomes using standard protocol and accelerated protocols in patients with progressive keratoconus. METHODS:CXL was performed using 3 epithelium-off protocols: standard [3 mW/cm for 30 minutes, 5.4 J/cm (S3/30-CXL)], accelerated with equivalent total irradiance [9 mW/cm for 10 minutes, 5.4 J/cm (A9/10-CXL)], and accelerated with increased total irradiance [30 mW/cm for 4 minutes, 7.2 J/cm (A30/4-CXL)]. Efficacy measurements were evaluated 12 months after treatment with Scheimpflug imaging (Pentacam HR) and included change in maximum keratometry (K Max), corrected distance visual acuity (CDVA), other keratometric variables, pachymetry, keratoconus indices, astigmatism, asphericity, manifest refraction, and higher order aberrations. RESULTS:Ninety-three eyes (67 patients) were evaluated: 35 eyes (26 patients) with S3/30-CXL, 29 eyes (19 patients) with A9/10-CXL, and 29 eyes (22 patients) with A30/4-CXL. Mean [INCREMENT]K Max was -1.53 ± 2.1 diopter (D) for S3/30-CXL, -0.71 ± 1.3 D for A9/10-CXL, and -0.70 ± 2.3 D for A30/4-CXL (P = 0.37). Mean [INCREMENT]CDVA(logMAR) was -0.18 ± 0.2 for S3/30-CXL, -0.13 ± 0.2 for A9/10-CXL, and -0.18 ± 0.2 for A30/4-CXL (P = 0.79). [INCREMENT]K Mean (r = -0.29 to -0.46), anterior asphericity (r = -0.34 to -0.40), and central keratoconus index (r = -0.18 to -0.38) best correlated with [INCREMENT]CDVA. S3/30-CXL had greater changes in index of surface variance, index of vertical asymmetry, keratoconus index, and regularization index compared to A9/10-CXL and A30/4-CXL. There were no other differences between protocols. CONCLUSIONS:All 3 protocols showed improvements in K Max, CDVA, and other variables, with similar functional outcomes for each despite greater change in keratoconus indices after S3/30-CXL. Correlations between change in measured variables and CDVA were poor overall; however, K Mean, central keratoconus index, and anterior asphericity were better correlated with CDVA than K Max.

Corneal cross-linking (CXL), introduced by Wollensak et al. in 2003, is a minimally invasive procedure to halt the progression of keratoconus. Conventional CXL is recommended in eyes with corneal thickness of at least 400 microns after de-epithelialization to prevent endothelial toxicity. However, most of the keratoconic corneas requiring CXL may not fulfill this preoperative inclusion criterion. Moderate-to-advanced cases are often found to have a pachymetry less than this threshold. There are various modifications to the conventional method to circumvent this issue of CXL thin corneas while avoiding the possible complications. This review is an update on the modifications of conventional CXL for thin corneas.

We describe the association of rapid progression of keratoconus in a 49-year-old woman on selective tissue estrogenic activity regulator (STEAR) therapy for endometriosis. Approximately 4 months after initiation of therapy with STEAR therapy and 3 months after ovariectomy, Scheimpflug images showed a massive increase in the previously stable ectasia. During this period, the maximum increase in the keratometry values was 2.7 diopters (D) in the right eye and 3.8 D in the left eye. Corneal crosslinking (CXL) was performed in both eyes. This resulted in excessive flattening of 5.5 D in the right eye and 6.1 D in the left eye at 9 months postoperatively. Patients having STEAR therapy must be monitored closely for corneal changes.