A New Model of Glaucoma Filtering Surgery in the Rat

PURPOSE

The most common reason for long-term failure of glaucoma filtering surgery (GFS) is scarring of the external filtering "bleb" tissues. The identification of the factors that mediate this process, as well as the development and initial testing of new therapies to limit scarring is enhanced by the use of appropriate animal models. The standard animal model for studying GFS is the rabbit but newer investigative tools that examine changes induced in biologic systems at a genetic level have made development of a rat model desirable.

METHODS

Glaucoma filtering surgery was performed on 20 Sprague-Dawley rats by introducing a 30-gauge silicone cannula through a penetrating scleral tunnel, under a limbal-based conjunctival flap and suturing the conjunctiva closed. Identical GFS was performed on 3 additional rats, which underwent histologic evaluation at days 2, 5, and 11, following surgery.Fistulizing surgery was also performed on 6 Sprague-Dawley rats, for comparison, by creating a full-thickness needle sclerostomy under a limbal-based conjunctival flap and suturing the conjunctiva closed.

RESULTS

Following the cannula GFS, well-elevated filtering blebs formed and these gradually failed over the course of 8 to 13 days. Needle tract sclerostomy filtering blebs formed at the site of the fistulizing surgery but rapidly failed over the course of 2 to 3 days.

CONCLUSION

Cannulated filtering surgery in the rat provides a longer lasting and more predictable model than needle tract sclerostomy for studying wound healing following GFS and may facilitate the study of induced changes at the gene level.

In vitro sensitivity of human Tenon's capsule fibroblasts to mitomycin C and its correlation with outcome of glaucoma filtration surgery

Dose-inhibition studies of proliferating fibroblasts grown from Tenon's capsule biopsy specimens obtained during trabeculectomy from 17 glaucoma patients were performed using varying concentrations of mitomycin C (MMC), with exposure of cells to the drug for either 5 days or 5 minutes. Surgical outcomes were determined 3 months postoperatively. Based on in vitro results, fibroblasts were classified as either MMC-"resistant" or MMC-"sensitive." Thirteen surgically successful cases were associated with 10 "sensitive" and three "resistant" fibroblasts; four surgical failures with one "sensitive" and three "resistant" fibroblasts. The in vitro studies were positively correlated with the clinical outcomes, the former correctly predicting the latter in 76.5% of the surgeries.

Single-plate Molteno implants in complicated glaucomas: results, survival rates, and complications

Sixty-two single-plate single-stage Molteno implantations for complicated glaucomas were performed between March 1991 and November 1992. The charts of all these patients were reviewed to determine the intraocular pressure (IOP) control success rate (< 21 mm Hg with or without medications), visual success rate (retention or improvement of visual acuity from preoperative level) and the rate of complications encountered. A Kaplan-Meier life-table (survival) analysis was also performed. IOP control was obtained in 74.2% of cases. Mean postoperative IOP was 16.97 +/- 8.07 mm Hg (Mean +/- SD). Visual success was obtained in 51.6% of the eyes. Eyes with aphakia/pseudophakic glaucomas showed the best response with 80% of them achieving IOP control and 60% achieving visual success. The survival plot for IOP control revealed 75.81% and 74.19% success rates at 48 and 72 weeks, respectively. Complications encountered were either due to the early postoperative hypotony or were tube-related. These results were gratifying considering the severity of the glaucoma in these cases and they reaffirm the usefulness of the Molteno implant in the management of difficult glaucomas.

Effect of the concentration and duration of application of mitomycin C in trabeculectomy

Ninety-three consecutive trabeculectomies in which mitomycin C (MMC) was applied intraoperatively, either at a concentration of 0.5 mg/mL for 5 minutes (n = 48) or at a concentration of 0.4 mg/mL for 3 minutes (n = 45), were reviewed to determine whether there was a significant difference between the two groups in terms of intraocular pressure (IOP) control and the incidence of complications. Preoperative and postoperative IOPs in the two groups did not differ significantly (P = .817 and .131, respectively). The 5-minute group had a higher incidence of serous choroidal detachments (P = .001). The incidence of postoperative hypotony and filtration failure with uncontrolled IOP in the two groups did not significantly differ (P = .177 and .582, respectively). Thus, intraoperative application of MMC at a concentration of 0.4 mg/mL for 3 minutes controlled postoperative IOP as effectively as MMC at a concentration of 0.5 mg/mL for 5 minutes, with a significantly lower incidence of choroidal detachments.

Familial nanophthalmos: management and complications

Nanophthalmos is a rare form of congenital hypermetropia, in which, the individual is at a high risk of developing angle-closure glaucoma. We report a family of nanophthalmos affecting a brother and sister, as confirmed by biometry. Genetic analysis revealed an autosomal recessive mode of inheritance. The sister developed angle-closure glaucoma, which was refractory to medical and laser therapy. She underwent surgical interventions which resulted in complications. The clinical presentation, management, and complications encountered are discussed.