COMPARATIVE STUDY OF THE ACTION OF THIOTEPA AND TRIAMCINOLONE ON CORNEAL VASCULARIZATION IN RABBITS

Treatments for corneal neovascularization: a review

Corneal neovascularization (CNV) may be a physiological response to various stimuli, but a chronic and persistent upregulation of neoangiogenesis can result in pathological CNV. Pathological blood vessels are immature and lack structural integrity, predisposing the cornea to lipid exudation, inflammation, and scarring. CNV can therefore become a potentially blinding condition. In this review, we frame CNV in an epidemiological perspective, consider risk factors for CNV, provide an overview of CNV pathogenesis, and consider the impact of CNV on corneal transplantation. We consider treatments that are of largely historical interest, before reviewing contemporary medical and surgical treatments. Within medical treatments, we report on steroids, nonsteroidal anti-inflammatory agents, antivascular endothelial growth factor agents, and cyclosporine. Within surgical treatments, we report on the use of lasers, photodynamic therapy, superficial keratectomy, and diathermy/cautery-based treatments.

Subconjunctival and intracorneal bevacizumab injection for corneal neovascularization in lipid keratopathy

PURPOSE

The purpose of this study was to evaluate the efficacy and safety of subconjunctival and corneal intrastromal bevacizumab injections on corneal neovascularization in patients with lipid keratopathy.

METHODS

Three eyes of 3 patients with lipid keratopathy accompanied by corneal neovascularization received at least 2 subconjunctival and corneal intrastromal injections of bevacizumab (1.25 mg/0.05 mL, respectively) at 1-month intervals. Ophthalmic examinations, including visual acuity, tonometry, slit lamp biomicroscopy, and corneal topography, were performed before injection and every month thereafter.

RESULTS

All patients had marked regression of corneal neovascularization. Reduction in lipid deposition was noted in one patient. There were no adverse ocular or systemic events, except for a small intracorneal hemorrhage noted in one patient, which quickly and spontaneously cleared.

CONCLUSION

Subconjunctival and intracorneal bevacizumab is a well-tolerated and effective method for obliterating corneal neovascularization in lipid keratopathy.

Laser photocoagulation of experimental corneal stromal vascularization. Efficacy and histopathology

BACKGROUND

Conventional treatment of corneal stromal vascularization is often inadequate. The authors developed a rabbit model of corneal stromal vascularization, treated it with laser photocoagulation, and then studied the histopathology.

METHODS

A reproducible model of corneal stromal vascularization was developed in albino rabbits by injecting sodium hydroxide into the corneal stroma. Corneal stromal vascularization was produced in both eyes of 13 rabbits, and treated after stabilization at 5 weeks with 577-nm yellow dye laser in 1 eye of each rabbit. Seven rabbits were followed for 6 months with corneal angiography and photography, and the corneal stromal vascularization quantified with a grid. The other 6 rabbits were killed at 1, 4, 8, 24, 48 hours, and 6 days after laser photocoagulation and examined by light and transmission electron microscopy.

RESULTS

Stable corneal stromal vascularization was observed in the anterior and midstroma for at least 6 months in the model. Laser photocoagulation reduced corneal stromal vascularization significantly compared with the controls (P < or = 0.05), resulting in 40.7% +/- 5.0%, 45.3% +/- 3.3%, and 34.9% +/- 5.2% (mean +/- standard error of the mean) reduction at 2, 4, and 6 months, respectively. Maximum inflammatory cell infiltrates were detected at 8 hours after laser photocoagulation, which diminished markedly at 6 days. The stroma of unlasered eyes showed no inflammatory cells and considerably more patent blood vessels than the lasered eyes. In the lasered eyes, transmission electron microscopy showed damaged vascular endothelial cells, extravasated erythrocytes, haphazardly arranged collagen fibrils, thrombus formation, and ghost vessels in the stroma. No damage was observed in the deep corneal stroma or endothelium in the lasered eyes.

CONCLUSION

Laser photocoagulation is effective in reducing corneal stromal vascularization in this model for at least 6 months. It does not damage the deeper stroma or endothelium.

Laser photocoagulation for corneal stromal vascularization

Images

Argon laser treatment of lipid keratopathy

Sixty-three cases of vascularised lipid keratopathy were treated with the argon laser to occlude feeder vessels which had been identified by fluorescein angiography. There was a reduction in extent in 62% and density in 49%. Visual acuity was improved in 48%. Six patients had keratoplasties shortly after treatment, none of which showed graft rejection. Minor complications included temporary haemorrhage into the cornea and iris atrophy. A more serious problem was severe corneal thinning after resorption of lipid. The patients had to be carefully followed up and maintained on a low dose of topical steroid.

Laser interactions with the cornea

Principles of laser-tissue interactions in the eye are reviewed. Corneal structure and function are summarized, with particular regard for features related to laser treatment. A summary of argon and carbon dioxide laser techniques in the cornea is presented, followed by a review of studies on corneal response to ultraviolet radiation. A detailed description is then given of the characteristics of excimer laser tissue ablation. Potential applications of this process in corneal and keratorefractive surgery are reviewed.

Treatment of lipid keratopathy with the argon laser

Twenty-two patients with lipid keratopathy were treated with argon laser photocoagulation to the feeder vessels. Two were grafted just over a week after treatment and the corneal discs examined histologically. The remainder of the patients were followed up for a least a year. In 6 cases the visual acuity improved, in 3 deteriorated, and in 10 did not change. The density and extent of the lipid deposition were diminished in 50% of cases. The commonest complications were bleeding into the lipid keratopathy and iris damage. The only serious problem was a disciform type of lipid keratopathy that flared up after treatment. Suggestions are made on improvements in the technique of laser application.

An evaluation of the role of leukocytes in the pathogenesis of experimentally induced corneal vascularization. II. Studies on the effect of leukocytic elimination on corneal vascularization

Investigations on several experimental models in the past have supported the hypotheses that corneal vascularization is a manifestation of the inflammatory response and that leukocytes perform an essential role in stimulating corneal vascular ingrowth. To evaluate the possible role of leukocytes further in this phenomenon, the effect of leukocyte elimination on corneal vascularization induced by silver nitrate cauterization was investigated. Weanling Fischer albino rats received doses of total body x-irradiation ranging from 1100 to 2100 rads to deplete circulating leukocytes, and corneal silver nitrate cauterization was performed 4 days later. In this model, animals that received 1500 rads or more total body x-irradiation became severely leukopenic within 4 days. As a rule, neither leukocytes nor blood vessels invaded the cauterized corneas, whereas both a leukocytic and vascular invasion occurred at lower doses of irradiation that did not totally eliminate circulating leukocytes. Corneal vascularization ensued if the corneal cauterization was performed immediately after total body x-irradiation with 1500 rads before the leukopenic effect of x-irradiation occurred. Control studies in which the cornea was cauterized 4 days after only the head received 1500 rads x-irradiation ruled out the possibility of irradiation-induced limbal endothelial damage as the explanation for the vascular suppression observed by x-ray treatment. In nonirradiated rats, silver nitrate cauterization of the cornea consistently induced corneal vascularization by 2 to 3 days. In further experiments, methylprednisolone acetate was administered subconjunctivally after corneal cauterization. This corticosteroid inhibited the infiltration of leukocytes and the subsequent vascular invasion into the corneal stroma, if administered immediately after silver nitrate cauterization. However, when the same glucocorticoid was administered 1 day after cauterization, both a leukocytic infiltration and vascular ingrowth occurred but to a less severe degree than in non-glucocorticoid-treated cauterized corneas. These investigations together demonstrated that a vascular ingrowth of the cornea did not follow corneal cauterization with silver nitrate in the absence of leukocytes, and gives further support to the hypothesis that leukocytes serve a crucial function in corneal vascularization.

Trtethylene Thiophosphoramide (Thio-Tepa) and Pterygium*

A 1:2000 solution of a radiomimetic alkylating agent-triethylene thiophosphoramide (thio-tepa, Lederle Laboratories) with a proven inhibitory action on proliferating vascular endothelium, was used topically as an adjunct to pterygium surgery in an attempt to decrease the incidence of recurrence. A bare-sclera technique, with excision of the pterygium, was the surgical method used. Two drops of 1:2000 solution of thiotepa (15 mg in 30 cc of Ringer's solution) were applied every three hours while awake from the second postoperative day for six weeks. Twenty-six eyes received this treatment. There was one recurrence in the period of follow-up, which has been up to three years. Four fellow eyes, operated on at the same time with the same surgical technique, received no topical thio-tepa postoperatively. Two of these eyes developed a recurrence of the pterygium. No sequelae related to corneal damage, defective vision, or interference with wound healing were observed. No systemic effects were encountered. It is concluded that thio-tepa, used as described, is a safe, inexpensive and valuable aid in pterygium surgery.