Minimum corneal diameter and anterior steep axis curvature share the same meridian: A novel finding

PURPOSE: To define the external scleral sulcus (ESS) on a Scheimpflug image and use it for a morphometric analysis of corneal diameter (CD). DESIGN: Retrospective, cross-sectional study of pediatric Asian-Indian eyes. METHODS: One random eye of 353 subjects between 5 to 18 years underwent 25-scan Pentacam HR imaging. For all scans, densitometry values along the anterior corneal edge were recorded and differentiated. The peaks on the differentiated curve were chosen as the ESS points and this distance between them was called CD. Vertical, (vCD), maximum (maxCD) and minimum (minCD) CD and their meridians were defined. Multiple regression models (MRM) with CD and other Pentacam parameters were built to predict astigmatism and its axis, mean keratometry (Kmean), and Belin/Ambrósio enhanced ectasia display deviation (BAD-D). MRM were validated using intraclass correlation coefficient (ICC). Estimated horizontal CD (hCD) was validated against digital caliper measurement using ICC. RESULTS: The ICC (95% CI) between caliper and hCD was 0.96 [0.93, 0.97]. MRM predictions (p<0.001) used CD parameters, anterior chamber depth, corneal volume and distance from the corneal thinnest-location to apex. These predictions achieved an ICC of 0.34 [0.18, 0.46], 0.82 [0.78, 0.86], 0.87 [0.84, 0.89] and 0.81 [0.76, 0.84], respectively. The astigmatism axis prediction depended on the minCD and maxCD meridians. Its within-subject standard deviation (4.97°) was less than two consecutive Pentacam scan angle (7.2°). CONCLUSIONS: The CD metric strongly correlated with the astigmatism axis, keratometry and BAD-D. Its spatial description may be significant in corneal treatment planning and disease diagnoses.