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Katja C. Iselin, Michael A. Thiel, Philipp B. Baenninger, Lucas M. Bachmann, Claude Kaufmann; Fluorophotometric determination of anterior chamber riboflavin concentrations. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4386. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal riboflavin saturation represents a prerequisite for crosslinking procedures with riboflavin "flare" in the anterior chamber (AC) serving as a surrogate for corneal saturation. In contrast to subjective slit-lamp biomicroscopy, fluorophotometry offers a more objective tool for the documentation of riboflavin in the AC. We therefore set out to evaluate fluorophotometry for the measurment of riboflavin fluorescence in an artificial AC model using human corneas.
Sets of riboflavin (Peschke® TE 0.25 %) dilutions ranging from 1-100,000 ng / ml were prepared. A modified Ocumetrics Fluorotron Master FM-2® fluorophotometer was used to measure the riboflavin concentrations of these sets in glass cuvettes. Nine human corneas not suitable for transplantation were placed on an artificial AC and perfused with a fixed volume of BSS® to take baseline fluorometric scans. The AC was flushed with the same fixed volume of increasing riboflavin concentrations and fluorometric AC scans were taken in triplicates across the cornea. Concordance between the logarithmically transformed concentrations in the glass cuvette and in the AC were graphically assessed using Bland-Altman-Plots and statistically tested using the Pitman test. A p-value <5% indicated a discordant result. The range of highest concordance was identified visually.
We obtained 93 pairs of concentration values from the glass cuvette and from the AC volume. The concentrations in the glass cuvette ranged from 1.78 ng/ml to 12379.72 ng/ml. The corresponding concentrations in the anterior chamber volume ranged from 2.52 ng/ml to 30906.42 ng/ml. The concordance of the logarithmically transformed values is shown in Figure 1. Across the whole spectrum of concentrations, the corresponding correlation coefficient between difference and mean r = -0.205 (p = 0.058) indicating a borderline discordance. By focusing on data in the range between 3 ng/ml and 7000 ng/ml, the concordance was markedly higher (r = -0.134, p = 0.338).
In vitro assessment of AC riboflavin concentrations with the Fluorotron Master FM-2® showed an accurate measurement across corneas, even for very low AC-concentrations. Discordances only occurred in the extremes of the dilution spectrum.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Figure 1: Bland-Altman plot of logarithmic cuvette and AC volume concentrations.
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