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The Lid Wiper Effect on Corneal Epithelial Thickness Pattern in Healthy Eyes as Characterized by Zernike Analysis
Hady Yazbeck1, Jad F Assaf1, Jiachi Hong1
1Casey Eye Institute, Oregon Health & Science University, Portland.
Purpose:
To develop quantitative biomarkers that characterize the effect of upper eyelid motion (lid-wiper effect) during blinking on corneal epithelial thickness.
Design:
A retrospective study analyzing corneal epithelium thickness maps through Zernike polynomial decomposition.
Subjects:
Three hundred thirty-six maps from 135 healthy eyes of 69 subjects.
Methods:
A total of 5-mm diameter epithelial thickness maps were acquired using spectral-domain OCT. Maps from left eyes were mirror-imaged and pooled with right eyes for analysis. Zernike polynomial decomposition was performed, and average coefficients were obtained. The lowest-order Zernike terms with single-angle dependence-tilt and primary coma-were analyzed as vectors to determine the lid-wiper axes. The lid-wiper gradient (μm/mm) and lid-wiper coma (μm) were calculated by projecting the tilt and coma vectors along their lid-wiper axes. Correlation analysis was performed between the lid-wiper gradient and lid-wiper coma, primary astigmatism, and higher-order aberrations.
Main Outcome Measures:
The lid-wiper gradient and lid-wiper coma, which are quantitative biomarkers of epithelial remodeling in response to the lid-wiper effect.
Results:
The average epithelial thickness map showed superotemporal thinning with relative inferonasal thickening. Average tilt and coma coefficients were nonzero (P = 0.004 to <0.001). The population centroids (mean ± standard deviation) of the lid-wiper gradient and lid-wiper coma were 0.51 ± 0.57 μm/mm at 298.06 ± 56˚, and 0.21 ± 0.55 μm at 311.59 ± 83.53˚, respectively. The lid-wiper gradient and coma were positively correlated with each other (R 2 = 0.08, P = 0.001).
Conclusions:
A significant epithelial thickness gradient exists in the average normal cornea, consistent with eyelid blink dynamics described in the literature. The significant but weak correlation between the lid-wiper gradient and coma suggests the lid-wiper effect may be among various factors contributing to higher-order aberrations in the epithelium. The lid-wiper gradient and coma may serve as quantitative biomarkers of epithelial remodeling in response to the lid-wiper effect.
Financial Disclosures:
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
