Ocular glucose extraction using vitreoperfusion in the cat

Quantitative methods to measure ocular glucose consumption in vivo, which is dominated by the retina, could provide considerable information about retinal metabolism in healthy and disease states. Eyes that are totally ischemic for at least 4 hr retain good retinal histopathologic features if treated with vitreoperfusion. In such cases, the vitreoperfusion fluid essentially is the only extraretinal source of glucose. We developed a mathematical model to estimate the rate at which glucose is extracted from the vitreoperfusion solution by metabolism (Eglu), compensating for losses via the outflow pathways. With a glass model eye (Eglu = 0) with a known, simulated outflow facility, the measured decline in glucose closely approximated the decline predicted by the equation (r = 0.97). In six formaldehyde-glutaraldehyde fixed cat eyes (Eglu = 0), the measured vitreous glucose concentrations at various times correlated with the calculated values (r = 0.96). With the use of general anesthesia, lensectomy and vitrectomy were performed in 10 cat eyes. Vitreoperfusion was initiated, and the cats were killed to establish total ocular ischemia. The mean +/- SD Eglu values for intervals between 15 and 75, 105 and 165, and 195 and 255 min after ischemia were 8.0 +/- 6.9, 14.4 +/- 10.4, and 19.9 +/- 11.0 micrograms/min, respectively (P less than .05). We conclude that the eyes retained their ability to extract glucose for at least 4 hr but that Eglu values increased during this period for undetermined reasons. In the future, measurements of Eglu may become useful in the evaluation of physiologic and pathologic states of the eye.