Characteristics of Corneal Astigmatism of Anterior and Posterior Surface in a Normal Control Group and Patients With Keratoconus.

PURPOSE: To evaluate and compare power and axis orientation of anterior and posterior astigmatism in eyes with keratoconus with healthy eyes. METHODS: In this retrospective cohort study, we examined 861 eyes of 494 patients diagnosed with keratoconus at the Department of Ophthalmology, University Hospital Frankfurt, and 256 eyes of 256 healthy individuals. Using a Scheimpflug device (Pentacam HR), we measured the magnitude and axis orientation of anterior and posterior corneal astigmatism, corneal thickness, and conus location. The results were compared between different stages of the disease according to the Amsler-Krumeich classification and the control group. RESULTS: Magnitude of corneal astigmatism was 3.47 ± 2.10 diopters (D) on the anterior surface and 0.69 ± 0.40 D on the posterior surface in eyes across all keratoconus stages. We found a significant increase of anterior and posterior corneal astigmatism with progression of disease (P < 0.01, 1-way analysis of variance) and a significant correlation between anterior and posterior corneal astigmatism (r = 0.77, P < 0.01). In contrast to eyes of healthy individuals, in which posterior corneal axis alignment is vertical in most cases independent of anterior alignment, we found in eyes with keratoconus a match between anterior and posterior alignment when alignment was vertical in 97% of eyes, 46% when oblique and 61% when horizontal (Cohen kappa coefficient κ = 0.55, P < 0.01). With progression of disease, alignment of anterior and posterior corneal astigmatism became increasingly vertical. CONCLUSIONS: In eyes with keratoconus, posterior axis alignment of corneal astigmatism is in line with alignment of the anterior surface in the majority of cases. Posterior astigmatism axis alignment could potentially be used in algorithms to support diagnosis and staging of keratoconus.

Effects of Atopic Syndrome on Keratoconus.

PURPOSE: To evaluate the effects of atopic syndrome on manifestations of keratoconus. METHODS: In this retrospective study, we reviewed patient files and data generated by Scheimpflug imaging of 670 eyes of 434 keratoconus patients. Patients were divided into a study group consisting of patients suffering from atopic syndrome (110 eyes of 75 patients), namely allergic asthma, atopic dermatitis, and/or allergic rhinitis, and a control group of patients without known atopic syndrome (560 eyes of 359 patients). RESULTS: We found a significant difference with the mean age being 36.1 ± 11.7 for the control group, 32.8 ± 9.6 for the atopic group (P = 0.002) with 1 atopic trait, and 30.4 ± 7.5 for patients with 2 or more atopic traits (P = 0.002). No statistically significant differences were found in the mean corrected distance visual acuity, corneal pachymetry, minimum relative pachymetric progression (RPImin), mean refraction, keratoconus index, anterior chamber depth and volume, Kmax, and location of Kmax in relation to the corneal apex. However, we found a significantly higher corneal density for the anterior 120 µm of the cornea in the atopic group (control: 20.74 ± 4.68, atopic group: 21.92 ± 4.65 P = 0.016). CONCLUSIONS: Keratoconus patients suffering from atopic syndrome were significantly younger but showed no topographical changes except in corneal densitometry compared with keratoconus patients without an atopic disease. This suggests atopic syndrome is a factor, which can trigger earlier manifestation of keratoconus.