Abstract
Purpose :
Corneal collagen crosslinking (CXL) is an accepted method to stop the progression of keratoconus and corneal ectasia. Recently, much effort has been put into developing CXL protocols that can reduce the time of the procedure without compromising the stiffening efficiency. Here, we use Brillouin microscopy to quantify corneal mechanical changes induced by CXL procedures of different irradiation time and power.
Methods :
Porcine cornea samples were exposed to a clinically-accepted 5.4 J/cm2 of UV-A illumination with varying time and power. Depth-sectional Brillouin maps were obtained so that the longitudinal modulus could be computed for the whole sample as well as for different depth sections of the cornea. For validation, using a compressive stress-strain test, the Young’s Modulus was found and compared for each irradiation condition.
Results :
The standard 3 mW/cm2 irradiance sample showed significantly larger increases in corneal stiffness compared to the 9, 34, and 50 mW/cm2 (P < 0.05). Within the cornea, the anterior and central sections of the 34 and 50 mW/cm2 conditions showed a decreased stiffening efficiency when compared to the standard 3 mW/cm2 sample. In the posterior cornea, all conditions produced significantly less stiffening than the standard protocol (P < 0.05). For all samples, the change in Brillouin-derived modulus correlated to the increase in Young’s Modulus (R2 = 0.99).
Conclusions :
Brillouin technology confirmed that, at constant illumination energy, higher UV-A light power over a shorter period of time results in suboptimal corneal stiffening. Beyond previous mechanical tests, Brillouin analysis revealed that the suboptimal stiffening effect is particularly prominent in deeper sections of the cornea.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.