Elsevier

Ophthalmology

Volume 107, Issue 7, July 2000, Pages 1328-1332
Ophthalmology

Changes in anterior and posterior corneal curvatures in keratoconus

https://doi.org/10.1016/S0161-6420(00)00159-7Get rights and content

Abstract

Objective

To quantitatively evaluate the changes in anterior and posterior corneal curvatures of eyes with keratoconus.

Design

Case-control retrospective and observational study.

Participants

Thirty-one patients who were clinically diagnosed to have unilateral or bilateral keratoconus and 18 normal subjects.

Intervention

The anterior and posterior topographies were obtained using scanning-slit videokeratography and assessed by Fourier series harmonic analysis.

Main outcome measures

Quantitative descriptors of the topography data, spherical power, regular astigmatism, and irregular astigmatism (asymmetry and higher order irregularity) components were compared between the anterior and posterior surfaces and among groups of clinically diagnosed keratoconus (33 eyes), keratoconus suspect (13 eyes), and normal subjects (36 eyes).

Results

Spherical power (P = 0.0003, Mann-Whitney U test with Bonferroni’s correction of P values), regular astigmatism (P = 0.0166), and asymmetry (P = 0.0031) of the anterior surface were significantly greater in the keratoconus eyes than in the normal controls. For the posterior surface, spherical power (P < 0.0001), regular astigmatism (P = 0.0143), asymmetry (P < 0.0001), and higher order irregularity (P = 0.0032) of the keratoconus group were significantly greater than those of the control group. The keratoconus suspect eyes, when compared with the normal controls, showed a significantly greater amount of spherical power (P = 0.0166) and asymmetry (P < 0.0001) in the anterior surface and spherical power (P < 0.0001), regular astigmatism (P = 0.0244), asymmetry (P < 0.0001), and higher order irregularity (P = 0.0276) in the posterior surface. All refractive components demonstrated statistically significant correlations between the anterior and posterior surfaces (P < 0.0001, Spearman’s rank correlation).

Conclusions

Not only the anterior but also the posterior corneal curvature is affected in keratoconus. These changes are observed from the early stage of this disorder.

Section snippets

Subjects and methods

Clinical records of 46 eyes of 31 patients, ranging in age from 10 to 42 years (24.0 ± 6.9 years, mean ± standard deviation) with bilateral or unilateral keratoconus were retrospectively evaluated. The patients were previously diagnosed as having keratoconus in both eyes or in one eye on the basis of the clinical features, slit-lamp findings, and/or videokeratographic signs obtained with placido disk videokeratography (TMS-2, Computed Anatomy Inc., New York, NY). In 31 patients, 15 were tested

Results

For the anterior surface, significant differences were found among the three groups in spherical power (P < 0.0001, Kruskal Wallis test), regular astigmatism (P < 0.0001), and asymmetry (P < 0.0001), but not in higher order irregularity (P = 0.2046) (Table 1). Spherical power, regular astigmatism, and asymmetry in the clinically apparent keratoconus eyes were significantly larger than those of normal controls (P < 0.0001, respectively, Mann-Whitney U test). Spherical power, regular astigmatism,

Discussion

For the anterior surface, keratoconus eyes exhibited a significantly greater amount of spherical powers regular astigmatism, and asymmetry than the normal controls. Similarly, the anterior surface of the keratoconus suspect eyes had significantly greater spherical power and asymmetry than the normal controls. In general, the most specific topographic changes in the anterior corneal curvature of keratoconus are central steepening and protrusion of the cornea usually inferior to the visual axis.15

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  • Cited by (0)

    1

    The authors have no commercial or proprietary interest in the product or company described in the current article.

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