We sought to determine if choroidal and outer retinal
deterioration occur with age in pigeons, as they do in
other species, and investigated the relationship between
age-related retinal and choroidal changes. In 64 pigeons
ranging in age over the pigeon lifespan (0.5–20 years),
we measured some or all among the following parameters:
choroidal blood flow (ChBF) by laser Doppler flowmetry,
choroidal thickness and choriocapillary vessel abundance
by LM histology, choriocapillary endothelial cell transport
specializations by EM histology, acuity by behavioral methods,
and degenerating photoreceptor abundance and total photoreceptor
abundance by LM histology. Regression and Receiver Operator
Curve (ROC) analyses were used to characterize the pattern
of age-related changes and determine the ages at or by
which significant changes occurred. For the 45 birds for
which we measured choroidal parameters, choriocapillary
vessel abundance showed a curvilinear decline with age
and half of this decline occurred by 3.5–4.6 years.
The endothelial cell transport specializations called channels
also declined curvilinearly with age. Choroidal thickness
was slightly increased between the ages of 3–6 years,
and thereafter declined steadily so that choroidal thickness
in the oldest birds was half that in the youngest. ChBF
showed an abrupt decline of about 20% at 4 years and a
further 20% decline thereafter. In the 53 birds for which
we obtained visual acuity and/or photoreceptor data, we
observed a curvilinear decline in acuity (with half the
decline having occurred by 8 years) and a prominent stepwise
decline of about 20% in photoreceptor abundance at 4.7
years, followed by further decline thereafter. The period
of major photoreceptor loss coincided with ages during
which about 10% of photoreceptors appeared to show degenerative
changes (4–8 years of age). Using partial correlation
analysis with the common effect of age held constant, ChBF
was found to have a positive correlation with acuity. Our
results show that ChBF and choroidal vascularity decline
significantly with age in pigeons, as do acuity and photoreceptor
abundance. Our statistical analyses suggest that prominent
choroidal vascular decline preceded the visual decline,
and that there is a positive relationship between choroidal
and visual functions. Thus, our findings are consistent
with the view that age-related decline in choroidal function
might contribute to age-related vision loss in pigeons.