Regional Variation in the Refractive-Index of the Bovine and Human Cornea

Purpose. Given the refractive importance of the human cornea, surprisingly little attention has been directed to the study of local variation in corneal refractive-index. This in vitro and in Vivo Study measures the refractive-index of different portions of the bovine and human cornea. Methods. Fifty fresh bovine corneas (obtained from an abattoir) and 10 human Subjects were used for the study. The refractive-index of the central, nasal, and temporal corneal epithelium was measured with a bench-top Abbe refractometer in the case of bovine corneas and with a hand-held refractometer with humans. Results. The mean (+/- standard deviation) refractive-indices of the central, nasal, and temporal bovine corneal epithelium were 1.3760 (+/- 0.003), 1.3757 (+/- 0.002), and 1.3746 (+/- 0.002), respectively. Refractive-indices of the anterior and posterior bovine corneal stroma were 1.3731 (+/- 0.002) and 1.3708 (+/- 0.004), respectively. The mean ( standard deviation) refractive-index in the central, nasal, and temporal periphery of the human cornea epithelium were 1.3970 (+/- 0.001), 1.3946 (+/- 0.001), and 1.3940 (+/- 0.001), respectively. Conclusion. There are small local differences in the refractive-index of the bovine and human corneal epithelium and the refractive-index of the epithelium is higher than that of the anterior and posterior stroma of the bovine cornea. (Optom Vis Sci 2008;85:977-981)