Spatial Variation in Vitreous Oxygen Consumption

Abstract

Purpose: The vitreous consumes oxygen via an ascorbic acid reaction with molecular oxygen. The spatiotemporal characteristics of this reaction, specifically within the eye, are not fully understood. We investigated the spatiotemporal variation of vitreous oxygen consumption in porcine cadaver eyes. Methods: Whole porcine eyes were obtained from a local slaughterhouse within 48 hours of enucleation. The native cornea and the lens were removed and replaced with a keratoprosthesis. Using a standard sclerotomy, a custom-made, semi-permeable oxygen delivery source was placed in two separate intravitreal locations (1 location per eye); the mid-vitreous (vitreous core) and posterior vitreous. A commercially made oxygen probe (Oxford Optronics) was used to measure the oxygen tension in various locations with respect to the oxygen delivery probe. For control experiments, the oxygen source was removed after the probe was positioned. After an hour in the dark, oxygen tension (pO_2) recordings were performed using a micromanipulator to retract the probe to desired distances (0, 1, 2, 3, 4mm) away from the oxygen source. A two-sided, two sample t-test was conducted to statistically compare pO_2 recordings. Results: In the presence of an oxygen source, mid-vitreous pO_2 and posterior vitreous pO_2 measurements are higher across all distances as compared to the control pO_2 measurements (N=4 for all groups). In the mid-vitreous experiments, there was a statistically significant difference between the oxygen source and control; (p<0.005) at all distances (0, 1, 2, 3, 4mm). In the posterior vitreous experiments, there was a statistically significant difference between oxygen source and control at all distances as well; 0mm (p<0.01), 1mm (p=0.01), 2mm (p<0.01), and 3mm (p=0.018) distances. Oxygen tension recordings are higher in the mid-vitreous compared to the posterior vitreous at all distances. The mid-vitreous oxygen tension is significantly different from the posterior vitreous oxygen tension at 2 and 3mm (p<0.001). Conclusions: Our data demonstrates that vitreous oxygen consumption is higher in the posterior vitreous compared to the mid vitreous. This may be important in understanding the role of vitreous cortex and vitreous core in oxygen homeostasis. These findings also have important implications in the modeling of oxygen consumption in the vitreous and eye.

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