IRIS:
The iris is the pigmented diaphragm separating the anterior and posterior chambers. It is joined to the ciliary body at the iris root. The anterior surface is composed of a condensed layer of fibroblasts, melanocytes, and collagen fibrils. The iris stroma contains melanocyts, fibroblasts, and blood vessels arranged in a loose network. The posterior surface of the iris is composed of two pigmented epithelial layers (Figure 2-9). The two layers have interwoven microvilli and are attached to each other laterally by desmosomes. The more anterior iris epithelial cells are fusiform in shape and extend myofilamentous cytoplasmic processes into the iris stroma (the dilator muscle). The posterior epithelial cells are columnar in shape. Both layers are densely pigmented (11). The iris is rarely sampled by cytologic techniques. However, normal iris may appear in intraocular washings from incidental ocutome cutting of the iris in an attempt to remove vitreous or lens fragments in the anterior chamber (Figure 2-10). Normal iris also may appear in fine needle aspiration specimens of iris neoplasms. In general, normal iris epithelium is so densely pigmented that cellular details are obscured (Figure 2-11). Iris stroma is characterized by the fine reticular meshwork of very cohesive and vascularized stroma.
LENS: The lens is an encapsulated, biconvex structure that is suspended by thin zonules that are attached to the ciliary body . The lens epithelium is located on the internal surface of the capsule. The interior of the lens is composed of cortical and nuclear cells. These hexagonally shaped anucleate cells are joined by interdigitations (
Figure 2-12). Because lens cells migrate anteriorly during embryogenesis, the posterior surface of the normal adult lens has no epithelium. Thus, the posterior surface of the lens covered only by a capsule (Figure 2-13). The lens is generally sampled during vitrectomy or lensectomy. The lens capsule can be identified on cytology preparations as a translucent (glass) membrane (Figure 2-14). This appears light green with Papanicolaou stain. Cortical fragments taken from the lens periphery or the bow sometimes demonstrate nucleated cells. Lens fragments appear as eosinophilic hexagonal structures by hemtoxylin and eosin, and light green with Papanicolaou stain (Figure 2-14). CILIARY BODY The ciliary body is composed of the ciliary processes, ciliary muscle, and ciliary epithelium (
Figure 2-15). About 70 radially arranged ciliary processes form the pars plicata anteriorly and are joined posteriorly with the smooth portion of the ciliary body, the pars plana (
Figure 2-1). The pars plana joins the retina and choroid at the ora serrata. The ciliary body is covered by two nonpigmented layer and an outer pigmented layer (
Figure 2-16). Under normal circumstances, ciliary body structures will not appear in vitrectomy specimens. However, ciliary epithelium may be sampled by fine needle aspiration of adjacent tumors. It is important to recognize the two-layered structure of the epithelium with abundant cytoplasm and large pigmented granules (Figure 2-17) (
12). VITREOUS The vitreous cavity is simply an expanded extracellular space that normally contains 4.0 ml of clear gelatinous substance that is composed largely of water, hyaluronic acid, and collagen (13). The vitreous normally contains anteroposterior oriented collagen fibrils and occasional macrophages or hyalocytes (
14). The presence of even small numbers of acute or chronic inflammatory cells within the vitreous is distinctly abnormal. The vitreous has distinct attachments to ocular structures (
15). It is attached anteriorly in a circumferential band extending from the posterior pars plana to a few millimeters behind the ora serrata in what has been termed the vitreous base. Traction exerted by the vitreous body at the base results in hyperpigmentation of the underlying pigment epithelium and is evident grossly (
16) (Figure below).
click on photo for a larger image
Above -dark pigmentation on the anterior border of the vitreous base (VB).
Below- transillumination highlights the pigmentation of the vitreous base as it straddles the ora serrata.
The vitreous is also attached to the retina over retinal blood vessels and at the optic disc (17). These attachments are important to understanding vitreous traction, retinal tears, and retinal detachment, for which vitrectomies are sometimes performed.
RETINA The sensory neuroepithelium of the eye is the retina, which is composed of many layers (Figure 2-18). These include the layer of outer and inner segments of the photoreceptor cells, the outer nuclear layer (cell bodies of photoreceptor cells), the outer plexiform layer, the inner nuclear layer, the inner plexiform layer, the ganglion cell layer, the nerve fiber layer, and the inner limiting lamina (membrane). The retina is loosely attached to the pigment epithelium, which is separated from the choroids by Bruch’s membrane. Normal and abnormal retina and pigment epithelium may be sampled in both vitrectomy and fine needle aspiration. In vitrectomy, the retina may be removed inadvertently. In cytologic preparations, the retina usually appears as a plexiform pattern of cells with round nuclei and characteristic organoid architecture (Figure 2-19). Often only small fragments of retinal tissue will be present, but can be recognized by the organoid architecture and distinctive nuclear halos (Figure 2-20). Occasionally, ganglion cells may be sampled (Figure 2-19). It is important for the cytologist to report retinal fragments discovered in intraocular washings because full thickness breaks in the retina may lead to retinal detachment. If the surgeon is made aware, the breaks may be closed with cryotherapy, laser, gas injection, or scleral buckle. Fragments of partial-thickness retina that have been stripped in the process of peeling membranes from the retinal surface are not uncommon in intraocular washings and are not regarded presently as clinically significant.
References:
11. Hogan et al., Histology of the human eye, 202-255.
12. Glasgow BJ. Intraocular fine needle aspiration of coronal adenomas. Diagn Cytopathol 1991;7:239-242.
13. Tolentino FI, Schepens CL, Freeman HM. Vitreoretinal disorders, diagnosis and management. Philadelphia: W.B. Saunders, 1976;1-43.
14. Sebag J, Balazs EA. Morphology and ultrastructure of human vitreous fibers. Invest Ophthalmol Vis Sci 1989;30:1867-1871.
15. Foos RY. Vitreoretinal juncture: topographical variations. Invest Ophthalmol Vis Sci 1972;10:801-808.
16. Foos RY. Anatomic and pathologic aspects of the vitreous body. Trans Am Acad Ophthalmol Otolaryngol 1973;77:OP171-OP183.
17. Gartner J. Histologische Beobachtugen uber physiologische vitreovaskulare. Adharenzen Klin Mbl Augen 1962;141:530-545.
