Quantitative analysis of iris parameters in keratoconus patients using optical coherence tomography

Lucas M Vianna,Beatriz Muñoz,David Friedman,Albert S Jun,Gustavo Bonfadini,Mauro Campos,Karun Arora

doi:10.5935/0004-2749.20150080

Abstract

To investigate the relationship between quantitative iris parameters and the presence of keratoconus. Cross-sectional observational study that included 15 affected eyes of 15 patients with keratoconus and 26 eyes of 26 normal age- and sex-matched controls. Iris parameters (area, thickness, and pupil diameter) of affected and unaffected eyes were measured under standardized light and dark conditions using anterior segment optical coherence tomography (AS-OCT). To identify optimal iris thickness cutoff points to maximize the sensitivity and specificity when discriminating keratoconus eyes from normal eyes, the analysis included the use of receiver operating characteristic (ROC) curves. Iris thickness and area were lower in keratoconus eyes than in normal eyes. The mean thickness at the pupillary margin under both light and dark conditions was found to be the best parameter for discriminating normal patients from keratoconus patients. Diagnostic performance was assessed by the area under the ROC curve (AROC), which had a value of 0.8256 with 80.0% sensitivity and 84.6% specificity, using a cutoff of 0.4125 mm. The sensitivity increased to 86.7% when a cutoff of 0.4700 mm was used. In our sample, iris thickness was lower in keratoconus eyes than in normal eyes. These results suggest that tomographic parameters may provide novel adjunct approaches for keratoconus screening.

Highlights

Keratoconus is traditionally described as a noninflammatory ectatic disorder of the cornea characterized by progressive thinning, steepening, and apical protrusion
We describe the novel use of anterior segment optical coherence tomography (AS-OCT) to determine iris parameters for discriminating between normal individuals and keratoconus patients
There was no apparent relationship between the iris parameters and severity of disease in the keratoconus patients

Summary

Introduction

Keratoconus is traditionally described as a noninflammatory ectatic disorder of the cornea characterized by progressive thinning, steepening, and apical protrusion. These corneal changes induce irregular astigmatism and myopic shift, causing impairment of vision. The incidence of keratoconus in the general population is estimated to be approximately 1 in 2000(1). Keratoconus is the second most frequent indication for corneal transplantation, accounting for approximately 12% of corneal transplants performed in the United States[2] and is one of the main indications of keratoplasty in Brazil[3]. The diagnosis of moderate-to-advanced keratoconus is not diffi cult because of the presence of irregular astigmatism on corneal topography and the development of classical clinical signs.

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Results

Conclusion