Laser Speckle Flowgraphy Reveals Widespread Reductions in Ocular Blood Flow in nonexudative Age-Related Macular Degeneration

Abstract

Purpose: To evaluate whether and where laser speckle flowgraphy (LSFG)-derived indices of ocular blood flow are reduced in non-exudative age-related macular degeneration (AMD) compared with age-matched control subjects.

Design: Retrospective case-control study.

Methods: Subjects with nonexudative AMD in the early, intermediate, or advanced stage underwent blood flow imaging with LSFG and were compared to age-matched control subjects. 39 eyes of 24 subjects with AMD and 41 eyes of 21 healthy controls were included. Mixed-effects models accounted for correlations between eyes in the same patient. Logistic regression evaluated the effect of ocular perfusion pressure and other factors associated with blood flow. Blood flow data was analyzed in 2 ways: by binary threshold for the primary analysis and through a superpixel-based method to map the territory of very low flow. The main outcome measure was choroidal blood flow and inner retinal blood flow in AMD and control eyes.

Results: Choroidal blood flow as measured by the LSFG in arbitrary units (AU) was reduced by 33% in AMD patients vs controls (5.3 ± 0.3 AU vs 7.9 ± 0.5 AU respectively, P = .00005). Inner retinal blood flow was also significantly reduced in AMD (12.5 ± 0.6 vs 15.6 ± 0.5 AU, P = .004). Ocular perfusion pressure showed no significant difference between AMD and control groups (50±5.5 vs 53±6.7 mm Hg respectively, P = .17), indicating that neither elevated intraocular pressure nor low blood pressure could account for the reduced blood flow. In most cases, the area of lowest blood flow was large and diffuse, exceeding the abnormal area affected by non-exudative AMD. Controlling for other subject and eye characteristics, an eye with 10%, 25%, or 50% below the average normal choroidal blood flow was more likely to have AMD, with an odds ratio of 2.27, 7.76, and 60.1, respectively (P = .026).

Conclusions: Laser speckle flowgraphy showed lower choroidal and inner retinal blood flow in non-exudative AMD patients compared to age-matched controls, not explained by low perfusion pressure. Areas of reduced blood flow greatly exceeded the territory of choroidal atrophy, emphasizing its role as a risk factor for the development and potential progression of dry AMD.