Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes.

Sepehr Feizi,Fatemeh Sadeghpour,Vahid Ownagh,Siamak Delfazayebaher,Mohammadali Javadi,Farid Karimian

doi:10.4103/jovr.jovr_19_17

Abstract

Purpose:To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.Methods:A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.Results:The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.Conclusion:Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.

Highlights

Keratoconus is a non‐inflammatory and progressive corneal disease with unknown etiology
Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups
Posterior corneal astigmatism could be predicted from keratometric astigmatism in the normal and keratoconus groups by using the following linear regression equations: posterior corneal astigmatism = −0.171 – 0.129 × keratometric astigmatism and posterior corneal astigmatism = −0.363 – 0.105 × keratometric astigmatism, respectively

Summary

Introduction

Keratoconus is a non‐inflammatory and progressive corneal disease with unknown etiology It leads to thinning and bulging of the cornea and, irregular. Detection of keratoconus among refractive surgery patients is crucial because the prevalence of keratoconus is higher in patients with such eyes than in the general population, and operating on an undetected keratoconic cornea is the major cause of post‐refractive surgery ectasia.[1,2,3] The diagnosis of clinical keratoconus is based on biomicroscopic findings along with additional paraclinical tests, such as pachymetry, keratometry, and corneal topography.[4] Placido disk‐based videokeratography and measurement of central corneal thickness are widely used methods in the diagnosis of keratoconus.[5,6,7] Placido disk‐based corneal topography examines only the central 7‐8 mm diameter of the anterior corneal surface, and is unable to evaluate the elevation of the posterior corneal surface, which is considered to be a significant feature, in early stage keratoconus detection.[8,9,10]

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