Nonlinear Optical Corneal Crosslinking, Mechanical Stiffening, and Corneal Flattening Using Amplified Femtosecond Pulses.

Purpose: We have shown that nonlinear optical corneal crosslinking (NLO CXL) and stiffening can be achieved in ex vivo rabbit corneas using an 80-MHz, 760-nm femtosecond (FS) laser, however the required power was beyond the American National Standard Institute limit. The purpose of this study was to test the efficacy of amplified FS pulses to perform CXL to reduce power by increasing pulse energy. Methods: A variable numerical aperture laser scanning delivery system was coupled to a 1030-nm laser with a noncollinear optical parametric amplifier to generate 760 nm, 50 to 150 kHz amplified FS pulses with 79.5-mum axial and 2.9-mum lateral two-photon focal volume. Ex vivo rabbit corneas received NLO CXL, and effectiveness was assessed by measuring collagen autofluorescence (CAF) and mechanical stiffening. NLO CXL was also performed in 14 live rabbits, and changes in corneal topography were measured using an Orbscan. Results: Amplified pulses (0.3 muJ) generated significant CAF that increased logarithmically with decreasing scan speed; achieving equivalent CAF to UVA CXL at 15.5 mm/s. Indentation testing detected a 62% increase in stiffness compared to control, and corneal topography measurements revealed a significant decrease of 1.0 +/- 0.8 diopter by 1 month (P < 0.05). Conclusions: These results show that NLO CXL using amplified pulses can produce corneal collagen CXL comparable to UVA CXL. Translational Relevance: NLO CXL using amplified pulses can produce corneal CXL comparable to UVA CXL, suggesting a potential clinical application in which NLO CXL can be used to perform personalized crosslinking for treatment of refractive errors and keratoconus.