CORRESPONDENCE

Echographic Evaluation of Primary Cysts of the Iris Pigment Epithelium

EDITOR: IN THEIR ARTICLE, "ECHOGRAPHIC EVALUATION OF PRI-mary cysts of the iris pigment epithelium," by P. A. Sidoti, M. Valencia, N. Chen, G. Baerveldt, and R. L. Green (Am J Ophthalmol 120:161-7, August 1995), the authors make the following undocumented state­ment: "Primary cysts of the iris pigment epithelium are rare developmental anomalies resulting from cystic expansion of the potential space between the pigment epithelial layers of the posterior iris."

Contrary to the authors' premise, light and elec­tron microscopic studies of spontaneous cysts of the iris root ciliary processes have demonstrated that they originate from a proliferation of the cells of the posterior iris epithelium or from cells of the inner, nonpigmented epithelium of the ciliary processes.1

The apices of the two epithelial cell layers remain tightly united, and no separation of the space between the two epithelial cell layers occurs in the formation of these cysts.

DAVID M. KOZART, M.D. Philadelphia, Pennsylvania

REFERENCE

1. Kozart DM, Scheie HG. Spontaneous cyst of the ciliary epithelium. Trans Am Ophthalmol Soc 1970;74:534-46.

AUTHOR REPLY WE APPRECIATE DR. KOZART'S COMMENTS WITH REGARD to the histologie aspects of primary cysts of the iris pigment epithelium. As he points out in his corre­spondence, our article makes reference to the com­monly reported histologie appearance of spontaneous iris pigment epithelial cysts; namely, fluid-filled cavi­ties, which form between the two pigment epithelial

layers of the posterior surface of the iris.1,2 Although the exact origin of these lesions is not clear, a developmental anomaly resulting in a localized sepa­ration of these two neuroepithelial layers and an expansion of the potential space between them is implied.

Dr. Kozart makes reference to a single histopatho-logic study in eight canine eyes of spontaneous cysts of the posterior iris ciliary processes.3 Light and electron microscopy were used to demonstrate the presence of an intact, double-layered epithelium along the outer wall of these cysts. Intercellular adhesions both within and between the two cell layers were intact and no expansion of the apical intercellular space was noted. The inner cyst wall appeared to originate from the inner epithelial cell layer by cellular proliferation.

All of the canine cysts described in this report involved the iris root or ciliary processes, or both. Interestingly, none involved the iris pigment epitheli­um solely or primarily. A review of human pathologic specimens yielded eight eyes with spontaneous epi­thelial cysts, which were noted to be similar in light microscopic appearance to their canine counterparts. No specific information regarding either the anatomic location or the clinical and histologie characteristics of this small number of human cysts was provided. The one human specimen examined by the authors was that of a ciliary body cyst.

We concur with Dr. Kozart's observations regard­ing the development of spontaneous epithelial cysts of the iris and ciliary body. These may, in certain cases, result from a proliferation of cells from the inner epithelial layer, with secondary expansion as these cells secrete fluid into the space between them and the posterior iris or ciliary surface. However, in other cases, different mechanisms appear to be in­volved. Given the ultrastructural differences between the posterior iris and ciliary body epithelia, it is possible that variability exists in the inherent tenden-

100 AMERICAN JOURNAL OF OPHTHALMOLOGY JANUARY 1996

cy for the two epithelial layers lining each of these structures to separate. The mechanism of cyst forma­tion may likewise vary in each of these locations. Only five (10%) of the cysts in our series were noted by echography to extend onto the anterior ciliary body. Thus, the vast majority of the lesions we studied were derived from cells with distinct ultra-structural features from the ciliary epithelium. This anatomic difference, along with the potential for interspecies variation, dictates caution in extrapolat­ing from the data of Kozart and Scheie3 to all neuroepithelium-derived cysts of the eye.

The primary purpose of our article was to elucidate further the clinical features of primary cysts of the iris pigment epithelium, and to describe the role of echography in assessing the location, extent, and internal structure of such lesions. It was not our intention to, nor did we, present evidence to support any particular theory as to the origin of primary iris cysts. We do, however, acknowledge that more than one mechanism may be involved in their formation,

and that the specific mechanism may vary between different lesions, different species, and different parts of the eye.

PAUL A. SIDOTI, M.D. New York, New York

GEORGE BAERVELDT, M.D. Cleveland, Ohio

MARCELA VALENCIA, M.D. NANCY CHEN, M.D.

RONALD L. GREEN, M.D. Los Angeles, California

REFERENCES

1. Reese AB. Spontaneous cysts of the ciliary body stimulating neoplasms. Am] Ophthalmol 1950;33:1738-46.

2. Shields JA. Primary cysts of the iris. Trans Am Ophthalmol Soc 1981;79:771-809.

3. Kozart DM, Scheie HG. Spontaneous cysts of the ciliary epithelium. Trans Am Acad Ophthalmol Otolaryngol 1970;74:534-45.

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