Abstract
Purpose: :
To assess thermal safety of the cornea during accelerated cross-linking with riboflavin at high UVA irradiances in vitro.
Methods: :
Pig eyes were received from an abattoir, de-epithelialized and ~100 µm thick corneal flaps were created with an automated Hansatome microkeratome. For each experiment, an eye with a thermocouple (K-type HH501DK, Omega Inc, Stanford, CT) inserted under the flap, was placed in an incubator (Model 12-140, Quincy Lab, Inc. Chicago, IL) and brought to 33 0C. Each eye was then irradiated with a 370 nm light source (UV LED NCSU033B(T), Nichia Co, Japan) and the temperature was recorded for 10 min. In addition, 0.2% riboflavin-5-phosphate solution (Sigma Aldrich, St. Louis, MO) in PBS containing 20% dextran was applied to the cornea every minute for 10 min. 9 corneas were irradiated with 370nm UV light with irradiances of 15, 150, and 225 mW/cm2, as measured with a power sensor (model PD-300-UV, Ophir, Inc., Jerusalem, Israel) and the rise of the temperature was recorded for 10 minutes.
Results: :
Thermocouple measurements of the corneal surface during UV irradiation with and without riboflavin showed a rise of temperature over the first few minutes, then becoming steady state. The steady state temperature measured increased approximately 2 0C at 15 mW/cm2 with and without riboflavin and 8 0C (without riboflavin) or 10 0C (with riboflavin) for both 150 and 225 mW/cm2.
Conclusions: :
Our data shows that the corneal temperature rise associated with accelerated cross-linking with riboflavin is safe at high UVA irradiances. Thermocouple measurements of the corneal surface performed in real time in vitro found that the steady state temperature achieved during accelerated cross-linking with riboflavin is significantly under the thermal injury thresholds of the cornea.
Keywords: cornea: basic science • photodynamic therapy • keratoconus