The Relationship between Axial Length, Retinal Function, and Oxygen Consumption: A Potential Protective Mechanism in Diabetic Retinopathy

Abstract

Purpose: A longer axial length (AL) has been shown to be protective for diabetic retinopathy (DR) although the mechanisms involved remain unclear. In this study, we evaluated the associations between AL, retinal function, and oxygen (O2) consumption to determine whether a decrease in retinal function in eyes with longer AL is associated with a reduction in metabolic demand; a hypothetical mechanism for the protective effect of an increased AL in DR development.

Methods: 36 healthy individuals with a range of AL (21.89 - 28.35mm) were recruited. AL, retinal function (determined by multifocal electroretinography [mfERG]) and O2 consumption (difference between arteriolar and venular O2 saturation levels), were measured in the right eye of each participant. Linear regression models were used to assess the associations of AL with mfERG P1 amplitudes and O2 consumption. Regression coefficients values (β), derived from path regression analysis models, were then used to explore the direct and indirect effects (via retinal function) of AL on O2 consumption.

Results: Longer AL was associated with reduced O2 consumption (per mm increase in AL: β = -1.37, 95% confidence interval [CI]: -1.95 to -0.77) and decreased retinal function (per mm increase in AL associated with changes in central amplitude: β= -0.18, 95% CI: -0.23 to -0.13; and peripheral amplitude: β= -0.47, 95% CI: -0.61 to -0.32). Increased retinal function was also associated with increased O2 consumption (per unit increased central amplitude: β = 0.39, 95% CI: 0.28 to 0.50; per unit increased peripheral amplitude: β = 1.06, 95% CI: 0.78 to 1.33). Path analysis including AL, retinal function and O2 consumption showed that AL had little direct influence on O2 consumption (β-= 0.004 and 0.06, respectively, in models with central and peripheral amplitudes as the intermediate variable) whereas the indirect effects on O2 consumption via changes in retinal function were greater (β= -0.62 and β= -0.68, respectively, in the same two models).

Conclusions: Eyes with longer AL have lower O2 consumption. The reduction in O2 demand is explained by the parallel reduction in retinal function. These findings are consistent with the hypothesis that the reduced O2 consumption in eyes with longer AL may help to reduce the risk of DR.

Keywords: 499 diabetic retinopathy