Purpose The purpose of this study was to examine the relationships between choriocapillaris (CC) and retinal pigment epithelial (RPE) changes in age-related macular degeneration (AMD). Morphological changes in the RPE/choriocapillaris complex were quantified in dry and wet forms of AMD and the results compared to with aged control eyes without maculopathy. Methods Postmortem choroids from 3 aged control subjects, 5 geographic atrophy (GA) subjects and 3 wet AMD subjects were analyzed using a semi-quantitative computer-assisted morphometric technique developed to measure percent RPE and CC areas in choroidal whole mounts incubated for alkaline phosphatase activity. The tissues were subsequently embedded in methacrylate and sectioned to examine structural changes. Results There was a linear relationship between the loss of RPE and CC in GA. A 50% reduction in vascular area was found in regions of complete RPE atrophy. Extreme constriction of remaining viable capillaries was found in areas devoid of RPE. Adjacent to active choroidal neovascularization (CNV) in wet AMD, CC dropout was evident in the absence of RPE atrophy resulting in a 50% decrease in vascular area. Lumenal diameters of the remaining capillaries in wet AMD eyes were similar to controls. Conclusions The primary insult in GA appears to be at the level of the RPE and there is an intimate relationship between RPE atrophy and secondary CC degeneration. CC degeneration occurs in the presence of viable RPE in wet AMD. The RPE in regions of vascular dropout are presumably hypoxic, which may result in an increase in VEGF production by the RPE and stimulation of CNV.

The purpose of this study was to examine the localization and relative levels of vascular endothelial growth factor (VEGF; an angiogenic factor) and pigment epithelium-derived factor (PEDF; an antiangiogenic factor) in aged human choroid and to determine if the localization or their relative levels changed in age-related macular degeneration (AMD). Ocular tissues were obtained from eight aged control donors (age range, 75-86 years; mean age, 79.8 years) with no evidence or history of chorioretinal disease and from 12 donors diagnosed with AMD (age range, 61-105 years; mean age, 83.9 years). Tissues were cryopreserved and streptavidin alkaline phosphatase immunohistochemistry was performed with rabbit polyclonal anti-human VEGF and rabbit polyclonal anti-human PEDF antibodies. Binding of the antibodies was blocked by preincubation of the antibody with an excess of recombinant human PEDF or VEGF peptide. Choroidal blood vessels were identified with mouse anti-human CD-34 antibody in adjacent tissue sections. Three independent observers graded the immunohistochemical reaction product. The most prominent sites of VEGF and PEDF localization in aged control choroid were RPE-Bruch's membrane-choriocapillaris complex including RPE basal lamina, intercapillary septa, and choroidal stroma. There was no significant difference in immunostaining intensity and localization of VEGF and PEDF in aged control choroids. The most intense VEGF immunoreactivity was observed in leukocytes within blood vessels. AMD choroid had a similar pattern and intensity of VEGF immunostaining to that observed in aged controls. However, PEDF immunoreactivity was significantly lower in RPE cells (p=0.0073), RPE basal lamina (p=0.0141), Bruch's membrane (p<0.0001), and choroidal stroma (p=0.0161) of AMD choroids. The most intense PEDF immunoreactivity was observed in disciform scars. Drusen and basal laminar deposits (BLDs) were positive for VEGF and PEDF. In aged control subjects, VEGF and PEDF immunostaining was the most intense in RPE-Bruch's membrane-choriocapillaris complex. In AMD, PEDF was significantly lower in RPE cells, RPE basal lamina, Bruch's membrane and choroidal stroma. These data suggest that a critical balance exists between PEDF and VEGF, and PEDF may counteract the angiogenic potential of VEGF. The decrease in PEDF may disrupt the balance and be permissive for the formation of choroidal neovascularization (CNV) in AMD.

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Background There is increasing evidence that inflammation and immune-mediated processes (complement activation) play an important role in age-related macular degeneration (AMD) pathogenesis. A genetic variation in the complement factor H (CFH) gene and plasma levels of C-reactive protein (CRP), a systemic marker of subclinical inflammation, have been consistently shown to be associated with an increased risk for AMD. In the present study, we examined the immunolocalization of CRP and CFH in aged control human donor eyes (n=10; mean age 79 yrs) and eyes with AMD (n=18; mean age 83 yrs). Methods Alkaline phosphatase immunohistochemistry was performed using polyclonal antibodies against CRP and CFH on cryopreserved tissue sections from disc/macular blocks. Three independent masked observers scored the reaction product (0-8). Results In aged control eyes, the retinal pigment epithelium/Bruch’s membrane/choriocapillaris (RPE/BrM/CC) complex including intercapillary septa (ICS) had the most prominent immunostaining for CRP and CFH. CRP was significantly higher than controls in BrM/CC/ICS and choroidal stroma in early and wet AMD eyes (p<0.05). In contrast, CFH was significantly lower in BrM/CC/ICS complex of AMD choroids than in controls (p<0.05). Interestingly, CRP and CFH were significantly reduced in BrM/CC/ICS complex in atrophic area of macula in geographic atrophy (GA)(p<0.05). Drusen and basal laminar deposits were intensely positive for CRP and CFH. Conclusion These immunohistochemical findings show that changes in distribution and relative levels of CRP and CFH were evident in early and late AMD eyes. This suggests that high levels of CRP and insufficient CFH at the retina/choroid interface may lead to uncontrolled complement activation with associated cell and tissue damage. This study supports the hypothesis that inflammation and immune-mediated mechanisms are involved in the pathogenesis of AMD.