Abstract
Purpose: :
To determine the effects of varying riboflavin concentration, presoak time, UVA irradiance, and duration of UVA exposure on corneal cross-linking with riboflavin measured by total corneal stiffness change using strip extensiometry.
Methods: :
Fresh whole rabbit eyes were obtained <24 hours postmortem in saline on ice from Pel-Freez biologicals (Arkansas). Eyes were brought to room temperature, epithelium was removed with a dull blade, intraocular pressure of 15mmHg was applied using a water column, and corneal thickness readings were taken through pachymetry. The eyes were subjected to varying riboflavin concentration, presoak time, UVA irradiance, and duration of UVA exposure. The eyes were left to rest for at least one hour before being excised leaving ~2mm scleral boundary. A 4mm strip was cut using parallel cutting blades from each cornea paying careful attention to orientation. Strips were placed in an extensiometer using rake like attachments with 5 tines (length 3mm) which were secured to the sclera on each side of the cornea. Strips were pulled at a constant rate of 10µm/min from a position where zero load was applied until either sample failure or the force limit of the load cell was reached.
Results: :
The increase in corneal stiffness for varying test conditions was consistent with expected predictions. Corneal stiffness increased proportionally with increasing riboflavin concentration, increasing soak time and increasing total energy dose.
Conclusions: :
The effects of varying riboflavin concentration, presoak time, UVA irradiance, and duration of UVA exposure on corneal cross-linking with riboflavin measured by total corneal stiffness change using strip extensiometry are consistent with expected predictions from our internal 2-D finite element analysis and photochemical kinetics models.
Keywords: cornea: basic science • photodynamic therapy