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O.-T. Lee, J. M. Stewart; Effects of Ultraviolet-A/Riboflavin Derived Modifications on Corneal Permeability and Flow Properties. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5984.
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To assess the influence of Ultraviolet-A (UVA) on corneal permeability and specific hydraulic conductivity (K) properties in an in vitro model.
Corneas obtained from rabbit eyes were used throughout this study. Samples were divided among three groups: 1) Untreated (control), 2) Untreated but with their epithelium mechanically removed, and 3) Treated with riboflavin and UVA and epithelium mechanically removed. Beginning 5 minutes before irradiation, group 3 samples were treated with a 0.1% riboflavin solution administered onto the debrided corneas and continued every 5 minutes until the end of the irradiation period. These corneas were irradiated with UVA light for 30 minutes at a distance of 3 cm from the corneal surface by using a custom built UVA emitter ( = 370nm). All corneas were mounted onto a two-chamber diffusion apparatus to determine permeability and K. Permeability across the tissue, characterized by means of a permeability coefficient, was measured by using fluorescence spectrometry to determine the diffusion of sodium fluorescein. In the flow study, the apparatus was connected to a fluid column and the descent of the fluid was measured to determine K.
The removal of the epithelial layer alone resulted in an increase in permeability and K compared to control tissue (n ≥ 4 for all groups). Corneal tissue crosslinked by the UVA treatment showed decreased permeability (1.63e-6 ± 1.55e-7 cm/sec) and flow (3.35e-16 ± 2.26e-16 m2) compared to the group that received only mechanical debridement (3.24e-6 ± 6.73e-7 cm/sec, 7.81e-16 ± 2.45e-16 m2, respectively). The decrease was statistically significant in both cases (p < 0.01).
Treatment with UVA and riboflavin decreases the permeability of both solute and solvent across the rabbit cornea. UVA crosslinking is able to overcome the increased permeability to both solute and fluid due to epithelial debridement alone. It is expected that permeability would be further reduced in vivo after epithelial healing has taken place.
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