The effect of photosensitizers on scleral permeability for ultraviolet A under the experiment
Aim. To compare the effect of water- and dextran-based photosensitizers on scleral permeability for ultraviolet A (UVA). Materials and methods. The study was performed on 20 cadaver porcine eyes subdivided into two groups. In group I, 0.1% aqueous solution of riboflavin mononucleotide was used. In group II, 20% dextran-based 0.1% solution of riboflavin mononucleotide («Dextralink») was used. Rectangular scleral flap sized 12*15 mm was created from each eye. Specimen thickness was measured using digital caliper. Scleral specimens were saturated with photosensitizer for 20 min. External surfaces of scleral flaps were exposed to UVA 3 mW/cm<sup>2</sup>. UV radiometer placed under the specimen was used to measure UV power which passes through the sclera for 30 min. Results. Scleral specimens saturated with dextran-based photosensitizer did not absorb UV completely. The power of transmitted UVA was 0.011±0.004 mW/cm<sup>2</sup> and increased with time. After 30 min, UVA power was 0.132±0.005 mW/cm<sup>2</sup>. An increase in scleral permeability resulted from scleral clarification due to its dehydration with dextran. Scleral specimens saturated with water-based photosensitizer completely absorbed UV. Moreover, this effect persisted during the entire follow-up. Conclusions. Scleral tissue of adequate thickness saturated with 0.1% water-based riboflavin may completely absorb UVA 3 mW/cm<sup>2</sup> thus preventing cytotoxic effect of UV on intraocular structures. Therefore, crosslinking with riboflavin/UVA may be safe in case of adequate scleral thickness and water-based photosensitizer use. Riboflavin with dextran should not be recommended since it promotes scleral dehydration and increases its permeability for UV.