Tissue Reaction to Intracorneal Silicone Rubber (Silastic RTV 382) and Methyl-2-Cyanoacrylate (Eastman 910 Adhesive)⋆

Pathogenetic and diagnostic aspects of siliconosis

Silicones have an adverse effect on human health well beyond that suggested by the recent superficial public controversy. The evidence for immune responses to injected/implanted silicones is extensive, detailed, often very specific, and not at all new. Comprehending the immunopathogenicity, realized and potential, of silicone has grown as our general understanding of the immune system has developed. Several major issues in furthering this comprehension pertain to the nature of the essential epitope, special risk of silicones to women, and definition of the chronic disease complex so evident clinically, one defying classification within currently traditional disease categories and states. The commentary presented here emphasizes the immunopathic evidence, explores the question of the essential epitope, estimates the minimal threshold of silicone load for immune reactivity, presents a profile of autoantibodies for siliconosis, and calls attention to specific silicone-based female contraceptive modalities. The silicone content of personal care products, not always revealed by retail package labeling, is explored as a potential sensitizing factor in the environment.

Tolerance of the rabbit cornea to an n-butyl-ester cyanoacrylate adhesive (Vetbond)

OBJECTIVE

An n-butyl-ester cyanoacrylate adhesive available for veterinary surgery (Vetbond, 3M) was tested in rabbits for corneal irritation.

PROCEDURES

Two experimental procedures were used on 24 rabbits: injection of the adhesive into an intralamellar corneal pocket (n = 10) and application of the glue to a mid-stromal corneal defect (n = 14). In both experiments the eyes were examined for 20 days for evidence of corneal irritation and tolerance. At the end of each experiment, histopathologic studies were performed on all corneas.

RESULTS

The corneal reaction to the intrastromally injected cyanoacrylate was characterized clinically by slight edema and vascularization localized to the vicinity of the adhesive. A moderate foreign body-type reaction was found histologically. Following application of the adhesive to a central stromal defect, the treated corneas remained totally clear and histopathologic examination showed that the healing process was not altered compared to the controls. The mean retention time of the glue patch was 14 days.

CONCLUSIONS

Intrastromal injection and surface application to a corneal defect of n-butyl-ester cyanoacrylate to a corneal defect induced only a mild inflammatory response and did not interfere with the reparative process. These findings suggest that this surgical adhesive would be acceptable for treating corneal ulcerations in animals.

The immunopathology of siliconosis. History, clinical presentation, and relation to silicosis and the chemistry of silicon and silicone

Recent evidence confirms the fundamental involvement of the human immune system in the reaction to implantation of silicone-based medical devices. An as yet-to-be particularized epitope of many complex substances sharing siloxane structures is presented through the MHC-II apparatus with development and retention of T cell memory. This memory can be tested for in practical terms using one or more forms of silica, which links the immuno-histopathology and autoimmune attributes of "silicosis" with those of "siliconosis." The lesions of siliconosis are typical of those for persistent antigens and delayed, cell mediated hypersensitivity. The basic descriptive pathology of the reaction to silicone has been known since soon after introduction of silicones in medical procedures, with the exception of some details related to the more recent discoveries on the role of cytokines in the immunopathic process. The clinical consequences of siliconosis are common and can be severe in some individuals implanted with silicone devices.

Surgical management of corneal ulceration and perforation

Corneal ulceration leading to perforation can occur secondary to a number of conditions, including infection, trauma, corneal dryness, and exposure keratitis. Because the ocular morbidity of corneal perforations is high, prompt diagnosis and treatment is critical. When persistent corneal ulceration does not respond to medical treatment, including antibiotics, therapeutic soft contact lenses, or tarsorrhaphy, surgical intervention is indicated. In this review, the evaluation of patients with recalcitrant ulceration or perforation is summarized, and indications and techniques for surgical treatment (epithelial transplantation, conjunctival flaps, lamellar and penetrating keratoplasty, tissue adhesives, periosteal grafts) are described.

The use of tissue adhesive in corneal perforations

Eighty patients with either corneal perforation or impending perforation were treated with the application of tissue adhesive that remained in place on the average of 50 days. Forty-four percent of these cases healed with the application of glue alone. Complications occurred in nine patients (11%). Two developed marked increase in intraocular pressure that was controlled with antiglaucoma medications and seven developed corneal infiltrates. Five of the infiltrates were culture-proven bacterial infections occurring on the average of 73 days after gluing. The relationships between diagnosis, duration of glue, and complications are reviewed.