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Laser photocoagulation of experimental corneal stromal vascularization. Efficacy and histopathology
V S Nirankari1, L Dandona, M M Rodrigues
1Department of Ophthalmology, University of Maryland School of Medicine, Baltimore.
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.