Regional differences in retinal vascular reactivity

PURPOSE. Although glaucomatous visual field defects are more common in the superior field than in the inferior field. microaneurysms are more frequent in the superior than in the inferior retina in diabetic retinopathy. The a uthors hypothesized that differences in vascular hemodynamics in the two ar eas might contribute to these phenomena. METHODS. The blood flow response to hyperoxia and hypercapnia mas evaluated in peripapillary retinal tissue superior and inferior to the optic nerve h ead using confocal scanning laser Doppler flowmetry. In 14 young, healthy p ersons, blood now was measured while breathing room air and during isocapni c hyperoxia (100% O-2 breathing) and isoxic hypercapnia. (Pco2 increased 15 % above baseline). Histograms were generated from pixel-by-pixel analysis o f retinal portions of superior and inferior temporal quadrants of the entir e image, RESULTS. Baseline blood flow in the inferior temporal quadrant was signific antly greater than in the superior temporal quadrant (P < 0.05. However, th e inferior region failed to increase in perfusion during hypercapnia and ex perienced significant mean blood non reduction; flow reduction in the pixel s at the 25th, 50th, 75th, and 90th percentile of now; and an increased per centage of pixels without measurable now, during hyperoxia teach P < 0.05). In contrast, in the superior temporal region, hyperoxia failed to reduce b lood volume, velocity, or flow,whereas hypercapnia significantly increased mean flow; increased flow in the pixels at the 25th, 50th, 75th, and 30th p ercentile of flow; and reduced the percentage of pixels without measurable flow (each P < 0.05). CONCLUSIONS. The inferior temporal quadrant of the peripapillary retina is, in comparison with the superior temporal region, less responsive to vasodi lation and more responsive to vasoconstriction. These differences could con tribute to different susceptibility to visual field defect or vascular dysf unction in the superior and inferior retina.