November 1971
Volume 10, Issue 11
Articles  |   November 1971
The Fine Structure of the Ciliary Zonule and Ciliary Epithelium
Author Affiliations
    Howe Laboratory of Ophthalmology, Harvard Medical School, Boston, Mass., and the Institute of Human Anatomy, University of Pavia, Italy
Investigative Ophthalmology & Visual Science November 1971, Vol.10, 851-869. doi:
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      GIUSEPPINA RAVIOLA; The Fine Structure of the Ciliary Zonule and Ciliary Epithelium . Invest. Ophthalmol. Vis. Sci. 1971;10(11):851-869.

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      © ARVO (1962-2015); The Authors (2016-present)

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The ciliary zonule has been studied with the electron microscope in the eye of the monkey, cow, and man, with the use of both thin sections and negatively stained specimens. The zonule consists of bundles or sheets of tubular fibrils, 110 to 120 Å in diameter. When loosely aggregated, they show a faint cross-striation without a clear-cut repeat pattern; when closely packed, they display an evident transverse banding with an average period of 490 Å. Zonular fibrils are digested by α-chymotrypsin and elastase, but they are not affected by collagenase. Therefore, they bear a striking resemblance to the microfibrils of the elastic fibers. At their origin from the ciliary body, the bundles of zonular fibrils perforate the inner limiting membrane, penetrate into the ciliary epithelium, and run a long, tangential path through the intercellular spaces of the nonpigmented epithelial layer, contained in interfacial canals which are directly bounded by the plasma membrane of the epithelial cells. At their insertion on the lens, the bundles of zonular fibrils fuse with the surface of the lens capsule; only in the human eye do they penetrate deeply into the substance of the capsule, approaching the surface of the lens epithelium and fibers. The cells of the nonpigmented layer of the ciliary epithelium have the complement of cytoplasmic organelles commonly found in secretory cells. They are connected to each other by desmosomes, gap junctions, and by a typical functional complex consisting of a zonula occludens and a zonula adhaerens. The facing apices of the nonpigmented and pigmented cells are joined by a row of gap functions and puncta adhaerentia; only in places do they diverge to enclose "ciliary channels," containing a moderately dense, amorphous material. In the distal part of the ciliary body, the nonpigmented epithelium contains occasional melanosomes and shows a more prominent basal labyrinth of interdigitating processes.


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