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Sanjay Anant Mahadik, Mohana KP, Sudhir RR, Prema Padmanabhan, Sangly P Srinivas; Influence of the Riboflavin Film on UV-A Penetration across Human Cornea. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3003.
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© ARVO (1962-2015); The Authors (2016-present)
Efficacy of collagen cross-linking across the corneal stroma in the treatment of keratoconus using Riboflavin (Rf) is dependent on the local levels of Rf itself, O2, and UV-A intensity. This study has investigated the influence of 20% dextran on the penetration of Rf and UV-A absorption across the cornea.
The thickness of the Rf film which formed after topical drop (~ 40 µL containing 0.1% Rf) with the subject in the supine position and eyes held open was measured by a high resolution OCT having a depth resolution of ~ 3 µm (Envisu™, Bioptigen) for 5 min. The thickness of the tear film following Na Hyaluronate (0.1%) and hyposmotic solutions (without dextran) drops were also measured. In an independent series of experiments, Rf levels across the stroma after similar topical Rf drops was measured for up to 30 min using a confocal scanning microfluorometer (CSMF; depth resolution ~ 8 µm) across pig cornea ex vivo.
Topical Rf drop (0.1 %Rf in 20% dextran of 500 kDa solution) produced a thick film which decreased in thickness slowly over 5 min (68, 56, 43, 32, 29, and 28 µm at 0, 1, 2, 3, 4, and 5 min, respectively; n = 3). In case of Na hyaluronate, the thickness reduced from 35 µm to 12 µm within 2 min (n = 3) and then a film break-up was evident. As expected, hyposmotic drops (viscosity of ~ 1 cp) produced very thin films, which vanished very rapidly (7.3 µm to 2.3 µm within 20-30 seconds; n = 3). The transcorneal Rf levels across pig cornea was significant after 30 min of dextran drop instilled on bare stroma (n = 10). However, the maximum Rf level in the anterior stroma was much smaller compared to 0.1% level in the drop.
The presence of the high MW dextran in the Rf drop produces a thick film of Rf on the stromal surface for at least up to 5 min and this permits penetration of Rf into the stroma. The Rf film with high concentration of Rf (~ 0.1%) and significant thickness (43 µm at 2 min) attenuates UV-A much more than Rf accumulated across the stroma. Thus, maintenance of a significant Rf film thickness by repetitive administration of the Rf drops is critical to prevent damage to endothelium during CxL.
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