Choroidal Changes in Rhesus Macaques in Aging and Age-Related Drusen

Abstract

Purpose : Choroidal vascular changes occur with normal aging and may also be associated with retinal diseases such as age-related macular degeneration (AMD). Here, we evaluate choroidal thickness and vascularity in rhesus macaques across their adult lifespan, and in animals that exhibit soft drusen, to determine the potential role of the choroid in the pathogenesis of this nonhuman primate model of AMD.

Methods : We analyzed spectral domain-optical coherence tomography (SD-OCT) images of 234 eyes from 117 rhesus macaques (range 4 - 32 years of age). Sub-foveal choroidal thickness (CT) measurements were performed using the Heidelberg Explorer software, while choroidal vascularity was measured by binarization using Niblack’s auto-local threshold to measure total choroidal area (TCA) and luminal area (LA), and to calculate stromal area (SA) and choroidal vascular index (CVI). Regression analyses were used to determine the relationship between CT and CVI with age, while Student’s t-tests were used to detect differences in CT and CVI in the presence or absence of soft drusen.

Results : Sub-foveal CT decreases with age at 3.2 µm/year (R² = 0.481, P < 0.001), while CVI also decreases over time at 0.67% per year (R² = 0.275, P < 0.001). Eyes with soft drusen exhibited thicker choroid (171.5 µm ± 12.2 µm vs. 137.4 µm ± 12.2 µm, P < 0.001) and higher CVI (0.606 ± 0.041 vs. 0.459 ± 0.107, P < 0.001) than age-matched control animals. In eyes with drusen, neither CT or CVI appear to be associated with drusen number, size, or volume.

Conclusions : Changes in choroidal vascular architecture in rhesus macaques resemble choroidal changes in human aging, although the relationship with age-related soft drusen in these animals appears less clear when compared to AMD in humans. The relative contribution of the choroid to drusen pathogenesis in monkeys may be different from its role in human AMD.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.