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G. A. Brummer, A. S. McCall, S. Littlechild, G. W. Conrad; Testing the Effects of Pyridoxal-5'-Phosphate on Riboflavin-Ultraviolet-A Induced Crosslinking for the Treatment of Keratoconus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6223.
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An amendment to the current treatment of keratoconus by riboflavin-ultraviolet-A cross-linking (RF-UVA) is proposed to reduce ultraviolet-A irradiation time.
Current treatment entails removing the epithelium from the cornea, followed by two consecutive thirty-minute topical applications of a 0.1% riboflavin (RF) solution to the cornea. During the second topical application of RF, the cornea is irradiated with long-wavelength UV light (UVA), 365 nm. To test the effects of PLP on this procedure, corneas were isolated from Spiny dogfish sharks (Squalus acanthias) and de-epithelialized; 1% PLP was added to the current 0.1% RF treatment solution and used in either both or just the first topical application. Strengthening effects were quantified by measuring the tensile force required to pull apart 2 mm strips of central cornea after treatments.
The additional application of a 1% PLP solution during both treatments blocks the effects of RF-UVA. However, application of PLP in only the first of the two topical applications, followed by sufficient rinsing to prevent singlet oxygen quenching by PLP, yields an increase in strength greater than the current RF-UVA treatment.
PLP can non-enzymatically convert native primary amine groups in the cornea to carbonyl groups, providing more sites for cross-linking, thus allowing possibly shorter exposures to UVA. The ability of PLP to to quench reactive oxygen species provides more evidence for PLP’s role as a biological antioxidant.
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