Hypoxia Induced Changes in the Total Attenuation Coefficient of the Human Cornea Measured In-vivo with Ultrahigh Resolution Optical Coherence Tomography

Abstract

Purpose: : To measure in-vivo time dependent variability of the optical attenuation coefficient of the human corneal stroma resulting from contact lens wear induced hypoxia.

Methods: : A research-grade UHROCT system was used to image in-vivo human cornea with 3.2µm axial and 10µm lateral resolution in non-contact lens wearers. Corneal edema was induced by inserting a thick, positive powered soft contact lens (SCL) and patching the eye for 3 hours. Corneal images were acquired prior to insertion, immediately after the removal of the SCL, and subsequently every 15 minutes for two hours. The images were segmented and straightened to accurately measure the stromal thickness. The data were corrected for spatial variations in the image contrast resulting from the corneal curvature and imaging beam focusing. The stromal optical attenuation coefficient was quantitatively accessed via linear regression analysis on the log-intensity data averaged over a single image.

Results: : About 10% stromal swelling was observed immediately after the removal of the SCL, while the stromal thickness returned to baseline in ~2h. Similarly, the stromal optical attenuation coefficient decreased over time with SCL wear and recovered to baseline in ~2h after the lens removal. Variability of the attenuation coefficient was observed between the anterior and posterior part of the stroma.

Conclusions: : The proposed method extracts unique features which are not related to image acquisition and unexpected noise. It also investigates features of the stromal region including probability distributions and their probable correlation in order to obtain a model for the attenuation coefficient variation behavior among individuals.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • image processing • cornea: basic science