Evaluation and Comparison of Corneal Ultrastructure in Normal and Keratoconic Eyes Using Spectral-Domain Optical Coherence Tomography
To identify Spectral-domain anterior segment optical coherence tomography (SD OCT) metrics that distinguish the corneal ultrastructure of normal eyes in comparison to keratoconic eyes. Specifically, this study aims to identify relationships between epithelial, stromal and total corneal thickness profiles and disease severity.
Retrospective review of 62 eyes (32 patients) with keratoconus and 63 normal control eyes (35 patients) were examined using the Optovue RTVue-100 (6 mm Pachymetry+Cpwr scans). Eyes were classified based on Keratoconus Severity Score and Amsler-Krumeich grading scales. The cornea was regionalized into 17 zones based on the OCT output map. Total, epithelial, and stromal pachymetry values were collected, as well as absolute minimum, epithelial minimum, and epithelial maximum pachymetry data. The data was then analyzed for trends in severity.
Keratoconus patients had a mean minimum epithelial thickness of 41.76±10.66 μm compared to 50.89±2.70 μm in control eyes (p<.001), and a mean maximum epithelial thickness of 62.61±8.25 μm compared to 57.68±2.56 μm (p<.001). The ratio of absolute minimum to absolute maximum corneal thickness in keratoconic eyes was 0.69±0.21 compared to 0.88±0.03 in control eyes (p<.001). The ratio of minimum epithelial thickness to the corresponding total corneal thickness values was also significantly different in control eyes compared with keratoconic eyes (p=.004). In addition, the ratios decrease as severity increases.
Corneal ultrastructure analysis using SD OCT can be useful in early diagnosis and severity stratification in keratoconus patients. The ratio of minimum epithelial thickness to total corneal thickness was shown to be a significant determinant of keratoconus severity correlating well with classical staging methods.