Retinal Oxygen Delivery, Metabolism and Extraction Fraction and Retinal Thickness Immediately Following an Interval of Ophthalmic Vessel Occlusion in Rats

Abstract

Limited knowledge is currently available about alterations of retinal blood flow (F), oxygen delivery (DO₂), oxygen metabolism (MO₂), oxygen extraction fraction (OEF), or thickness after the ophthalmic blood vessels have been closed for a substantial interval and then reopened. We ligated the ophthalmic vessels for 120 minutes in one eye of 17 rats, and measured these variables within 20 minutes after release of the ligature in the 10 rats which had immediate reflow. F, DO₂ and MO₂ were 5.2 ± 3.1 μL/min, 428 ± 271 nL O₂/min, and 234 ± 133 nL O₂/min, respectively, that is, to 58%, 46% and 60% of values obtained from normal fellow eyes (P < 0.004). OEF was 0.65 ± 0.23, 148% of normal (P = 0.03). Inner and total retinal thicknesses were 195 ± 24 and 293 ± 20 μm, respectively, 117% and 114% of normal, and inversely related to MO₂ (P ≤ 0.02). These results reflect how much energy is available to the retina immediately after an interval of nonperfusion for 120 minutes. Thus, they elucidate aspects of the pathophysiology of nonperfusion retinal injury and may improve therapy in patients with retinal artery or ophthalmic artery obstructions.

Figure 1

Relationship between inner retinal thickness and inner retinal oxygen metabolism (MO₂) in rats with normal fellow and nonperfusion eyes. Data from the normal fellow eyes (black) are connected to the corresponding data obtained from the eyes immediately after 120 minutes of total ocular nonperfusion (red). An inverse linear relationship was found between increases in inner retinal thickness values and nonperfusion-induced reductions in MO₂ values (β = −0.093 µm * min * nL O₂⁻¹, P = 0.019, N = 9).

Figure 2

Relationship between total retinal thickness and inner retinal oxygen metabolism (MO₂) in rats with normal fellow and nonperfusion eyes. Data from the normal fellow eyes (black) are connected to the corresponding data obtained from the eyes immediately after 120 minutes of total ocular nonperfusion (red). An inverse linear relationship was found between increases in total retinal thickness values and nonperfusion-induced reductions in MO₂ values (β = −0.12 µm * nL O₂⁻¹ * min, P = 0.006, N = 9).