Timing of Age-Related Changes in the Choroid and Retina of Pigeons

Abstract

Abstract: : Purpose: We sought to determine the relative timing of age-related declines in the retina and choroid of pigeons for the purpose of determining if choroidal changes precede and might thus be causal to retinal declines. Methods: In pigeons ranging over a substantial portion of the pigeon life span (0.5-20 yrs), we measured the following parameters: basal choroidal blood flow (ChBF) by laser Doppler flowmetry (LDF), evoked parasympathetic vasodilation of choroidal vessels by central stimulation and LDF, parasympathetic choriodal innervation by immunohistochemistry, choriocapillary vessel abundance (CC), and photoreceptor abundance by LM histology. We focused on the superior quadrant of the eye, since it is the area of highest photoreceptor density in pigeons. The measured parameters were analyzed statistically using regression and receiver-operator characteristic (ROC) analysis to characterize the shape and pace in their age-related change. Results: Evoked parasympathetic choroidal vasodilation, parasympathetic choroidal innervation, and CC all showed a significant curvilinear decline with age. Using the regression equations for these parameters, we found that half of the total loss had occurred by about 3.2 years of age. By contrast, basal ChBF showed an abrupt decline at around the age of 4 years, while photoreceptor abundance showed an abrupt decline around the age of 4.6 years, with both showing more gradual decline thereafter. Conclusions: Using statistical methods, we found that major losses in neurogenic control of ChBF, in choriocapillary vessel abundance, and in basal ChBF precede a precipitous decline in photoreceptors in pigeons as they age. The results suggest that age-related decline in choroidal function early in the pigeon lifespan could contribute to subsequent age-related retinal declines.

Keywords: aging • choroid • blood supply