OCT based corneal densitometry: the confounding effect of epithelial speckle

Corneal densitometry is a clinically validated method for objectively assessing the transparency of stroma. The technique is currently dominated by Scheimpflug technology. Still, optical coherence tomography (OCT), in which examination of the statistical properties of corneal speckle is undertaken, has also been considered to assess corneal densitometry. In-vivo, the stroma is observed via the epithelium. However, the effect of this external layer on stromal densitometry has not been considered as yet. This study aims to quantify the influence of epithelium integrity on corneal OCT densitometry. OCT images from eleven freshly enucleated porcine eyes before and after epithelial debridement were used. OCT densitometry was investigated at different stromal depths using four metrics of speckle statistics. Results indicate that there exist statistically significant differences in speckle statistics for a given stromal depth depending on the presence or absence of the epithelium. The estimation error in speckle statistics can reach over 20% depending on the stromal depth. The anterior stroma densitometry values are the ones most affected by epithelial integrity. In conclusion, if OCT densitometry stromal parameters are to be considered in absolute terms, it is essential to consider the confounding effect of the epithelial layer in the analysis.