Three-dimensional architecture of the suspensory apparatus of the lens of the Rhesus monkey.

Abstract the three-dimensional ultrastructure of the lens suspensory apparatus and its supporting tissues were determined in the adult Rhesus monkey eye, Single zonular bundles (4–6 μm) composed of parallel oriented fibrils were traced from the lens surfaces to the ciliary body. There are four major tracts of zonular fibrils; the anterior lens to pars plana, the equatorial region to ciliary process, the posterior lens to pars plana, and the posterior lens to ciliary process to pars plana. The course and insertion patterns of the anterior and posterior zonules suggest separate functions. The anterior zonules are arranged in a pattern suited for anterior face contour changes required in accommodation. The posterior zonular pattern is better arranged for maintenance of lens position. The anterior hyaloid membrane is seen as a mesh-work of fibrils with attachments around the ora serrata and on the lens posterior. It also serves as a lens support structure. In contrast, the adjacent vitreous is composed of fibrils plus globular units which are probably hyaluronic acid. The construction of the ciliary processes, the inserting posterior zonules, and the circumferential fibrils between the ciliary processes form a complex capable of reversible response to ciliary muscle contraction. In the light of these findings, a reconsideration of the prineipal theories of accommodation is in order.