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PurposeTo indirectly measure stromal riboflavin penetration using commercially available riboflavin solutions and new and existing epithelium‐off, trans‐epithelial and iontophoresis‐assisted delivery protocols.MethodsForty porcine eyes were divided into eight groups. Group 1: Ricrolin applied to the de‐epithelialised cornea for 30 min; Group 2: epithelium‐intact, no treatment; Groups 3–5: epithelium‐intact, 30‐min application of Ricrolin TE, Mediocross TE or ParaCel/Vibex, respectively. Group 6: epithelium‐intact, Ricrolin+ iontophoresis‐assisted delivery for 5 min; Group 7: epithelium‐intact, Ricrolin+ iontophoresis‐assisted delivery for 5 min with a 20‐min riboflavin soak; and Group 8: epithelium‐intact, Ricrolin+ iontophoresis‐assisted delivery for 5 min, 15‐min soak and another 5 min of iontophoresis. After a saline wash, light transmission spectra were obtained from each cornea, before and after epithelial removal.ResultsCorneas in groups 1 and 8 showed a distinct riboflavin absorption peak between 400 and 520 nm. The optical density of the corneas in groups 3–7 did not differ significantly from that of the untreated corneas (group 2).ConclusionsA modification to the standard iontophoresis trans‐epithelial technique resulted in successful penetration of riboflavin into the stroma and appears to offer the most promise for epithelium‐on cross‐linking.

Citation: O'Brart NAL, O'Brart DPS, Aldahlawi NH, Hayes S, Meek KM. An investigation of the effects of riboflavin concentration on the efficacy of corneal cross-linking using an enzymatic resistance model in porcine corneas. Invest Ophthalmol Vis Sci.

The aim of this study was to investigate corneal enzymatic resistance following epithelium off and on riboflavin/UVA cross-linking (CXL). One hundred and fourteen porcine eyes were divided into four non-irradiated control groups and seven CXL groups. The latter comprised; (i) epithelium-off, 0.1% iso-osmolar riboflavin, 9 mW UVA irradiation for 10 min, (ii) disrupted epithelium, 0.1% hypo-osmolar riboflavin, 9 mW UVA for 10 min, (iii) epithelium-on, 0.25% hypo-osmolar riboflavin with 0.01% benzylalkonium chloride (BACS), 9 mW UVA for 10 min, (iv) epithelium-on, 5 min iontophoresis at 0.1 mA for 5 min with 0.1% riboflavin solution, 9 mW UVA for 10 min or (v) 12.5 min, (vi) epithelium-on, prolonged iontophoresis protocol of 25 min with 1.0 mA for 5 min and 0.5 mA for 5 min with 0.25% riboflavin with 0.01% BACS, 9 mW UVA for 10 min or (vii) 12.5 min. Enzymatic resistance was assessed by daily measurement of a corneal button placed in pepsin solution and measurement of corneal button dry weight after 11 days of digestion. This study revealed that the enzymatic resistance was greater in CXL corneas than non-irradiated corneas (p < 0.0001). Epithelium-off CXL showed the greatest enzymatic resistance (p < 0.0001). The prolonged iontophoresis protocol was found to be superior to all other trans-epithelial protocols (p < 0.0001). A 25% increase in UVA radiance significantly increased corneal enzymatic resistance (p < 0.0001). In conclusion, although epithelium-on CXL appears to be inferior to epithelium-off CXL in terms of enzymatic resistance to pepsin digestion, the outcome of epithelium-on CXL may be significantly improved through the use of higher concentrations of riboflavin solution, a longer duration of iontophoresis and an increase in UVA radiance.

No author has a financial or proprietary interest in any material or method mentioned.

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