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Arie Marcovich, Alexander Brandis, Ilan Feine, Iddo Pinkas, Ruth Goldschmidt, Vyacheslav Kalchenko, Daniel Wagner, Yoram Salomon, Avigdor Scherz; Long term follow-up of stiffening of rabbit corneas by WST11 using near infrared light. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5289.
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To evaluate the efficacy and safety of photochemical corneal stiffening by Pd- bacteriochlorin 13’-(2-sulfoethyl)-amide dipotassium salt (WST11) and near infrared (NIR) illumination, using rabbit eye models.
Corneas of living rabbits were pretreated topically with 2.5 mg/ml WST11 in saline or in 20% dextran T-500 for 20 minutes, and illuminated with a NIR diode laser (755 nm, 10 mW/cm2) for 30 minutes. Corneas of untreated fellow eyes served as controls. The rabbits were sacrificed after one month and 4 months. Corneal strips of 4 mm width were excised. Ultimate stress and Young’s modulus measurements were performed using a biomechanical tester. Comparative studies were performed with standard riboflavin/ultraviolet-A light (UVA) treatment. Histology, electron spin resonance, fluorescence microscopy and optical coherence tomography (OCT) were used to evaluate treatment effects.
WST11/NIR treatment significantly increased corneal stiffness following treatment, compared to untreated contralateral eyes. After 1 month the ultimate stress and Young’s modulus of treated corneas increased by 113%, and 80% respectively. WST11 in 20% dextran T-500/NIR had similar stiffening results, but markedly reduced post-treatment edema and time of epithelial healing compared to WST11 without dextran. After 4 months, treated corneas maintained biomechanical stiffness values measured at 1 month post treatment. OCT demonstrated a demarcation line in the anterior third of the corneal stroma. Histology showed a reduction in the keratocyte population in the anterior half of the corneal stroma, without damage to the endothelium. Electron spin resonance demonstrated that WST11/NIR generates hydroxyl and superoxide radicals but no singlet oxygen in the cornea. These results, in particular when combined with additional optical spectroscopy techniques, suggest a novel mechanism for corneal stiffening that has not been so far anticipated in connection with current stiffening approaches.
Treatment of rabbit corneas, with the bacteriochlorophyll derivative WST11 and NIR illumination, increased their biomechanical strength through mechanism that does not involve singlet oxygen. WST11 in 20% dextran T-500/NIR treatment showed less adverse effects. This treatment may have a potential for clinical use in keratoconus and corneal ectasia.
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