Recently we reported measurements of the corneal in-depth light backscattering distribution (CDLBD) by optical coherence tomography (OCT) as a possible tool for investigation of the corneal hydration and estimation of water gradients inside the cornea.
In this paper, we present additional results demonstrating a strong correlation (R = 0.99) between the amplitude of light backscattering as measured by OCT and the corneal thickness. In contrary to the well-known effect of the immediate increase observed in corneal opacity during corneal swelling, we observed an initial decrease of the amplitude of light backscattering as measured by OCT in the anterior part of the stroma during the swelling process. The possible explanation for this observation is discussed. Also methodological improvements for accurate measurements of the CDLBD in vivo are outlined.
The knowledge of water content of the cornea (hydration level H) can provide crucial information for the assessment of corneal function. The correlation between the corneal thickness and its hydration enables us to estimate H indirectly by measuring changes in corneal thickness and scattering using OCT. The magnitude and axial distribution of the backscattering signal from the cornea yields additional information about the hydration gradient across the cornea. We present data on the effect of corneal hydration on its thickness and scattering in natural processes of de- and rehydration, as well as in stress tests with the use of glycerol-based dehydrating agent Ophthalgan. Our data demonstrate that scattering signal changes up to 50 times when corneal thickness varies from 60% to 200% of its normal state. The distribution of scattering intensity across the cornea also depends on the hydration level and gradient of the water distribution. Thus, OCT can provide a noninvasive and non-contact method for safe and fast measurement of thickness and optical properties of the cornea, and therefore, for estimation of corneal hydration level and corneal function.