Clinical evaluation of flat peripheral curve design with aspherical-curve and multi-curve hard contact lenses for keratoconus.

Aspherical- and multi-curve rigid gas-permeable hard contact lenses (HCLs) have a flattened curve in the peripheral zone and are mostly used for patients with keratoconus who cannot wear glasses, soft contact lenses, or spherical HCLs. In this retrospective study, a total of 95 eyes of 77 patients who used aspherical- or multi-curve HCLs (mean age: 40.0 ± 11.0 years) were evaluated. This study examined the types of aspherical- and multi-curve HCLs, best-corrected visual acuity (BCVA) values before and after wearing HCLs, the association with the Amsler-Krumeich classification, duration of wear, corneal/conjunctival disorder, and the frequency of changing HCLs. There were 78 eyes that used aspherical-curve HCLs and 17 that used multi-curve HCLs. BCVA significantly improved from 0.42 logMAR to 0.06 logMAR after wearing either form of HCL. The Amsler-Krumeich classification showed that aspherical-curve HCLs were commonly used for patients with stage 2 keratoconus, and multi-curve HCLs were commonly used for stage 4 patients. The BCVA values were worse when the disease stage was more severe (stages 3 and 4) regardless of HCL type. The mean base curve of the lenses was steeper in multi-curve HCLs than in aspherical-curve HCLs. The more severe the disease stage, the steeper the base curve in both aspherical- and multi-curve HCLs. The duration of wear significantly improved from 2.1 h to 10.2 h, and corneal/conjunctival disorder similarly improved. The mean frequency of changing HCL types was 1.1 times. This study suggests that a flat peripheral curve design with aspherical- and multi-curve HCLs is useful for patients with keratoconus.

Correlation of corneal elevation with severity of keratoconus by means of anterior and posterior topographic analysis.

PURPOSE: To investigate the severity of keratoconus in terms of corneal elevation differences with 2 different reference surfaces using topographic analysis. METHODS: Eighty-six eyes of 50 patients with keratoconus of various clinical stages (61 male and 25 female eyes) with mean age of 37.3 ± 11.6 years were evaluated. Anterior and posterior corneal elevations were measured using topographic analysis (using a rotating Scheimpflug camera), and the imaging data were analyzed to estimate elevation differences as differential values from conventional best-fit-sphere and enhanced best-fit-sphere (exclusion of a 4-mm-diameter area from the most thinned cornea). The data correlated with the keratoconus severity index and Amsler-Krumeich classification of keratoconus. RESULTS: There was a significant positive correlation between elevation differences and keratoconus severity index in both anterior and posterior surfaces (Pearson correlation coefficient, r = 0.66; P < 0.001; r = 0.74; P < 0.001). Cases of larger elevation differences in the anterior and posterior corneal surfaces were staged higher in Amsler-Krumeich classification (1-way analysis of variance, P = 0.040; P < 0.001). Cases of lower staging in the Amsler-Krumeich classification had a larger area under the receiver operating characteristic curve in the posterior elevation differences than in the anterior elevation differences, suggesting a greater diagnostic value of the posterior elevation measurement. CONCLUSIONS: Anterior and posterior corneal surface height data obtained by elevation-based tomography provide useful information in improving keratoconus diagnostic accuracy and in grading the severity of keratoconus.

Effect of higher-order aberrations on visual function in keratoconic eyes with a rigid gas permeable contact lens.

PURPOSE: To study the effect of higher-order aberrations (HOAs) on visual function in keratoconus with a rigid gas permeable (RGP) contact lens (CLs). DESIGN: Retrospective nonrandomized study. METHODS: Thirteen eyes of 10 subjects with keratoconus who wore a RGP CLs (KC-RGP group), 15 eyes of nine normal subjects (normal group), and 14 eyes of nine subjects who wore a RGP CLs (RGP group) who had no ocular diseases except for refractive errors and had 20/20 or better-corrected visual acuity were included in this study. The root-mean-square (RMS) of the third-, fourth-, fifth-, and sixth-order Zernike coefficients (total HOAs), the RMS of the third-order Zernike coefficients (S3) (coma-like aberration), the RMS of the fourth-order coefficients (S4) (spherical-like aberrations), and the area under the log contrast sensitivity function (AULCSF) were evaluated. RESULTS: The AULCSF in the KC-RGP group was significantly lower than in the other two groups. The total HOAs, S3, and S4 in the KC-RGP group were significantly higher than in the other two groups. There were significant negative correlations between the area under the log contrast sensitivity function and the total HOAs, S3, and S4. CONCLUSIONS: The visual performance in a keratoconic eye with a RGP CLs degrades compared with normal eyes with and without RGP CLs, even if the corrected VA is good. The degradation is assumed to be related to residual HOAs in a keratoconic eye with a RGP CLs.