Oxygen Dynamics across the Cornea

  • Sahana Damale, D.R. Ramesh Babu, S.P. Srinivas

Abstract

The corneal transparency is mainly determined by physiological mechanisms dependent on oxygen (O2) metabolism in its cellular layers. The O2 metabolism of the whole cornea and the contribution of the cellular layers were first investigated with electrochemical approaches and then by non-invasive optical methods. The non-invasive methods are based on sensing O2 tension (pO2) underneath contact lenses. The optical methods employ O2-sensitive phosphorescent dyes coated onto the inner surface of test contact lenses. Since the pO2-sensitive luminescent dyes undergo dynamic quenching by O2, their phosphorescence or fluorescence lifetimes (t) are related to pO2 as per the Stern-Volmer equation. The changes in t have been measured in the time domain (TD), but the frequency domain (FD) methods can offer unique advantages for transcorneal measurements. In the TD approach, the phosphorescence/fluorescence decay is recorded and analysed for t in response to a pulsed excitation. On the other hand, in the FD approach, phase delay (j) and demodulation (M) relative to a modulated excitation is detected and analysed for t. A simple implementation of the FD approach embodies a lock-in amplifier to detect j and M in response to sine modulation of excitation. A frequency spectrum of j and M is determined by high-speed pulsed excitation in the digital frequency domain (DFD) techniques. We provide a summary of FD approaches that have been developed for transcorneal pO2 measurements using a custom-made confocal scanning microfluorometer. Overall, advanced fluorescence technologies enable further understanding of corneal O2 metabolism in health and disease with and without contact lenses.

Published
2021-11-08
How to Cite
Sahana Damale, D.R. Ramesh Babu, S.P. Srinivas. (2021). Oxygen Dynamics across the Cornea. Design Engineering, 10568 - 10577. Retrieved from http://www.thedesignengineering.com/index.php/DE/article/view/6114
Section
Articles