Abstract
Purpose: The goal of the study is to measure the group refractive index of the human cornea in vitro to improve the accuracy of corneal thickness measurements. Methods: Corneal buttons were trephined from 23 human cadaver eyes and the group refractive index of the cornea was measured at lambda equals 840 nm using a low-coherence Michelson interferometer and the technique proposed by Sorin and Gray (Phot. Tech. Lett. 4:105 - 107, 1992). The effect of dehydration on the measurement was studied by measuring the corneal optical thickness as a function of time. Results: Preliminary measurements of the group refractive index at 840 nm gave n
equals 1.450 plus or minus 0.024 for the human cornea, which is much higher than a calculated group refractive index of n
equals 1.387. Because of dehydration, the optical thickness of the cornea decreased at a rate of 5.5 micrometer/minute which led to an artificially high value for the group refractive index. Conclusion: The calculated group refractive index of n
equals 1.387 appears to be an accurate value for the purpose of corneal thickness measurements using low-coherence interferometry, and corneal group refractive index measurements can be performed in vitro if the measurements are performed rapidly to avoid the effect of dehydration.
