G. Lutty et al., Changes in choriocapillaris and retinal pigment epithelium in age-related macular degeneration, MOL VIS, 5(24-35), 1999, pp. NIL_70-NIL_73
Retinal pigment epithelial cells (RPE) and the choriocapillaris are on oppo
site sides of Bruch's membrane and control transport in and out of the reti
na. In age-related macular degeneration (AMD), they may also be responsible
for deposition of material in and on Bruch's membrane and the formation or
regression of choroidal neovascularization (CNV). Indocyanine green (ICG)
angiography can be used to visualize the choroidal vasculature and CNV. Fil
ling of the choriocapillaris with ICG was delayed in subjects older than 50
years of age, and areas of hypofluorescence were observed in maculas of AM
D subjects, often associated with CNV. Laser Doppler flowmetry of the chori
ocapillaris in the macula demonstrated that choroidal blood flow and volume
are reduced in subjects older than 46 years of age and further decreased i
n subjects with AMD. The human choriocapillaris can be histologically studi
ed in two dimensions by incubating the tissue for alkaline phosphatase acti
vity, flat-embedding it in transparent polymer and sectioning it. Using thi
s technique, choriocapillaris dropout was found to be associated with depos
ition of material in Bruch's membrane in diabetic subjects. When RPE are re
moved from Bruch's membrane, the choriocapillaris degenerates; the regenera
tion of choriocapillaris can be blocked by Genistein, a tyrosine kinase inh
ibitor. Finally, RPE cells may produce substances that both stimulate the f
ormation and regression of CNV in animal models. These studies suggest that
there may be a reduction in choriocapillaris flow in AMD, and this loss of
choriocapillaris can be associated with the Bruch's membrane deposits that
are hallmarks of AMD. Furthermore, RPE may stimulate the formation and reg
ression of CNV and RPE loss can result in loss of choriocapillaris.