Abstract
Purpose :
To determine the effects of pulsed versus non-pulsed, high intensity ultraviolet light (UVA) crosslinking on corneal elasticity and viscosity.
Methods :
Three pairs of donor human eyes kept in damp gauze storage containers were obtained from the Florida Lions’ Eye Bank for this study. The corneas were excised from the globes beyond the limbus, the epithelium was removed from each cornea with a cotton swab, and the corneas were placed into a vial containing 20% Dextran and stored overnight to restore the corneas to a near physiological hydration state. The corneas were then pre-treated with 20% riboflavin every 5 minutes for a total of 30 minutes. The left corneas (OS) underwent high intensity UVA crosslinking with an intensity of 9mW/cm2 for 10 minutes using the Peschke cornea crosslinking system (total surface dose of 5.4J/cm2). The right corneas (OD) underwent the same intensity UVA, but the light was pulsed with a pulse on/pulse off time of 10 seconds and 10 seconds, respectively (same surface dose of 5.4J/cm2). Corneal hydration was maintained throughout the crosslinking by applying riboflavin every 5 minutes. After crosslinking, the corneas were allowed to equilibrate in 15% Dextran for 30 minutes. A microkeratome (Moria Evolution 2) with a 50μm head was then used to expose the anterior stroma in each cornea. An atomic force microscope, custom designed for biomechanical measurements, was used to assess the elasticity and viscosity at the anterior stromal layer of each cornea.
Results :
For two out of the three pairs of corneas investigated, the corneas that underwent pulsed UVA crosslinking were significantly stiffer than their non-pulsed counterparts (2.33 and 2.86 times greater Young’s modulus). The viscosity was also significantly greater in these pairs (3.85 and 2.69 times greater). The third pair of corneas had comparable stiffness and viscosity for both pulsed and non-pulsed protocols.
Conclusions :
These preliminary results suggest that high intensity, pulsed crosslinking is more effective than the same UVA intensity applied continuously at increasing the elastic modulus of the cornea; this suggests that pulsing the ultraviolet light could increase the efficacy of accelerated, non-pulsed procedures.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.