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Elias Pavlatos, Yuli Yang, David Huang, Yan Li; An Epithelial Modulation Index to Distinguish Keratoconus from Corneas with Contact Lens-Related Warpage. Invest. Ophthalmol. Vis. Sci. 2020;61(7):4745.
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© ARVO (1962-2015); The Authors (2016-present)
To develop an epithelial modulation index (EMI) for differentiating keratoconus from corneas with contact lens (CL)-related warpage.
Maps of epithelial thickness and mean curvature of the anterior cornea were generated using a Fourier-domain OCT system (Avanti, Optovue, Fremont, CA) and custom MATLAB algorithms. Keratoconus and warpage cases were diagnosed based on clinical and topography findings. Normal participants had no corneal abnormalities and no history of ocular surgery. Normal and keratoconic eyes had no recent CL usage (soft CL within 1 week or rigid gas permeable CL within 3 weeks). Pattern deviation (PD) maps were computed to show differences relative to normal population maps (averaged from 50 normal eyes not included in this study). The EMI was calculated as the covariance between the epithelial thickness and mean curvature PD maps within the central 5 mm diameter of the cornea. The area under the ROC curve and the classification accuracy of the EMI were evaluated. The classification cutoff value was calculated as the upper limit of the 99% confidence interval of the EMI for warpage eyes.
91 eyes from 65 keratoconus patients, 20 eyes from 10 warpage patients, and 32 eyes from 16 normal subjects were analyzed. In keratoconus, epithelial thickness maps showed focal thinning near the apex of the cone while mean curvature maps showed anterior steepening (Fig. 1). This was in contrast to warpage cases for which the epithelium was thicker and the mean curvature was flatter (Fig. 2). The EMI was more negative for keratoconic eyes (mean ± SD = -134.9 ± 103.2, range -586.5 to -10.8) than for warpage eyes (2.4 ± 8.3, -6.6 to 34.9; p < 0.0001). The EMI was also low for normal corneas (1.2 ± 1.4, range -0.9 to 4.2). The area under the ROC curve was 1.0 (95% CI = 0.97-1.0) for differentiating keratoconus from warpage eyes. With a cutoff value of -6.1, the accuracy for the EMI was 95% (19/20) for warpage eyes and 100% (91/91) for keratoconus eyes.
The EMI is useful in distinguishing eyes with secondary epithelial modulation (keratoconus) from those with primary epithelial deformation (CL-related warpage).
This is a 2020 ARVO Annual Meeting abstract.
Figure 1. Epithelial thickness and mean curvature PD maps for a keratoconus case (EMI = -164.4).
Figure 2. Epithelial thickness and mean curvature PD maps for a CL-related warpage case (EMI = 2.1).
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