Morphologic proof of the toxicity of mitomycin C on the ciliary body in relation to different application methods

Background: Since postoperative hypotony has been a frequent complication o f glaucomatous filtration surgery with adjunctive use of mitomycin C (MMC), the question arises of whether there may be another application method whi ch can minimize this side effect. The purpose of this study was to establis h the morphologic side effects of different application methods. Methods: M MC 0.2 mg/ml was applied to the episclera of nine eyes of six pigmental rab bits at random via collagen shield (CS), soft contact lens (CL), or lyophil isate (20 mu g; LY) for 5 min. Two eyes (controls) had a subconjunctival in jection of BSS only. Another control eye was left untreated (no injection). No trabeculectomy was performed. One hour later the amounts of MMC in the conjunctiva and aqueous were analyzed by reverse-phase high-pressure liquid chromatography. Ciliary bodies were dissected from the enucleated eyes, em bedded and investigated by transmission electron microscopy (TEM). Cell hei ght of the nonpigmented ciliary epithelium was morphometrically assessed by means of computer-assisted image analysis. Results: The light-microscopic analysis of the sectioned cell area revealed reduction of the cell height o f the non-pigmented ciliary epithelium (NPCE) after application with soft c ontact lens (foufold) and collagen shield (2.5-fold) but not with lyophilis ate compared to the untreated eye. The following ultrastructural changes we re seen: loss of apical microvilli (CS, CL, LY), disintegrating melanin gra nules within NPCE (CS), lysis of entire areas with NPCE cells (CS), myelin figures within mitochondria (LY), intracellular vacuoles (CS, CL), lysis of myelinated nerves (CS), myelin figures in mitochondria of endothelial cell s (LY), and lysis of stromal fibrocytes (CS). In the control eyes (injectio n of BSS) none of these ultrastructural changes were detected in the cylind rical NPCE cells. The concentration of mitomycin in the aqueous humor after topical application of MMC on the episclera for 5 min were all below the d etection limit (<10 ng/ml). The concentration of MMC in the conjunctiva ran ged from 2.1 to 3.7 mu g/g. Conclusion: Severe morphologic alterations were seen at the electron-microscopic level after application of MMC 0.2 mg/ml with a collagen shield and with a soft contact lens. They were mildest with lyophilisate and absent in the BSS controls. A new administration device i s needed if trabeculectomy is to be performed successfully using MMC in hum an glaucomatous eyes.