[Morphometric analysis of age-dependent changes of the human ciliary body]

Morphometric and stereologic techniques have been applied to human ciliary epithelium and bordering stroma of 31 (respectively 16) normal donor eyes aged 15 to 86, providing quantitative information on the age-related structural changes of ciliary body tissue. Aging appeared to result in a generalized widening of the stromal layer from 19.3 +/- 2.4 microns (10-20 years; n = 4) to 60.0 +/- 11.5 microns (80-90 years; n = 3) in ciliary processes and from 53.0 +/- 6.8 microns to 107.6 +/- 15.2 microns in the ground plate between ciliary valleys and ciliary muscle, a density increase of collagenous fibers from 39.3 +/- 4.9 to 83.5 +/- 14.6 fibers/microns 2 and a concomitant decrease in mean fiber diameter from 62.8 +/- 3.4 nm to 55.7 +/- 1.5 nm, a decline of stromal cell density from 31.4 +/- 1.8 to 9.6 +/- 1.0 cells/0.014 mm2, a progressive thickening of the inner and outer limiting membranes from 0.8 +/- 0.4 micron to 8.1 +/- 1.5 microns and 2.1 +/- 0.6 microns to 4.5 +/- 0.5 microns respectively as well as the endothelial basement membrane from 0.13 +/- 0.004 micron to 0.25 +/- 0.03 micron, a gradual widening of the perivascular space between capillaries and overlying pigment epithelium from 6.2 +/- 1.5 microns to 11.3 +/- 2.9 microns, an increase in number of fenestrations in the capillary endothelium from 39.0 +/- 8.5 to 69.0 +/- 7.0 pores/100 microns, and finally a continuous augmentation of degenerative elements including lipids, lipofuscin granules, and lysosomes from 1.5 +/- 0.06% to 7.2 +/- 0.6% within the non-pigmented epithelium (NPE) over the 71-year period studied. Regression analysis yielded a highly significant impact of age on these morphometric parameters, while the relative volumes of the remaining cell compartments of the NPE-cells revealed no statistically significant correlation with age. Rather, the variations in volume densities of Golgi bodies (0.34 +/- 0.25%; n = 16) and pigment granules (0.36 +/- 0.27%; n = 16) seemed to be random with respect to age, whereas the relative volumes of mitochondria (21.7 +/- 1.8%; n = 16) and RER (5.9 +/- 0.7%; n = 16) remained fairly constant indicating that the NPE-cells maintain their functional capacity with advancing age. Age-related reduction of aqueous humor formation therefore appears to be rather due to impaired fluid passage from vasculature to ciliary epithelium than to functional incompetency of the NPE.