Purchase this article with an account.
DW Hahn, KA McDow, BT Fisher, MH Goldstein; Assessment Of Transient Changes In corneal Hydration Using Confocal Raman Spectroscopy . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1708.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose:The degree of corneal hydration has been linked to excimer laser corneal ablation rates. Enhanced precision with excimer laser refractive surgery may be obtained by a better understanding of the transient changes in corneal hydration that may occur as a result of de-epithelization and lifting of the LASIK flap. Methods:Confocal micro-Raman spectroscopy (632.8 nm excitation) was used to measure relative corneal hydration. The Raman scattering intensity ratio of water OH peaks to collagen protein CH peaks was used to quantify hydration. Water and acetone solutions were used to establish a quantitative response of the relative OH/CH Raman bands. Enucleated bovine eyes were the source of corneas. The corneas were either mechanically de-epithelized or had lamellar corneal flaps created to expose the underlying stromal tissue. Raman spectra were recorded every 30 seconds for 6 minutes while the prepared corneal surfaces were exposed to quiescent air or to a low flow of nitrogen across the surface. Results:The OH/CH ratio exhibited a linear response (near unity slope) with the acetone/water ratio as the percentage of acetone was varied from 0 to 100%. The ratios of the OH/CH Raman bands at the corneal surface were found to increase by about 10% and 20% after six minutes in quiescent air for the de-epithelized and exposed stroma corneas, respectively. The increase in OH/CH ratio was approximately linear over this period. In contrast, the ratios of the OH/CH Raman bands were found to decrease by about 30% and 20% after six minutes of exposure to the nitrogen flow for the de-epithelized and exposed stroma corneas, respectively. Conclusion:Raman spectroscopy is a quantitative method for assessing the relative degree of corneal hydration. Stromal surface hydration increases slightly following de-epithelization or removal of corneal flaps when exposed to quiescent air. The increase in hydration is presumably due to diffusion of water to the surface following removal of natural barriers, namely the epithelium or the corneal flap. In contrast, when exposed to a low flow rate of gas, stromal surface hydration is decreased as water diffuses from the cornea to the gas stream. The increase in mass transfer at the gas flow interface most likely exceeds the rate of diffusion of water to the corneal surface.
This PDF is available to Subscribers Only