In Vivo Femtosecond (FS) Laser Machined Transepithelial (TE) Nonlinear Optical Corneal Crosslinking (NLO CXL) Compared to FS Laser Machined TE Ultraviolet (UVA) Corneal CXL

Abstract

Purpose : While UVA CXL is an effective Keratoconus treatment, epithelial debridement for optimal stromal riboflavin (Rf) permeability causes post operative discomfort, delayed visual recovery, and enhanced risk of infection. We have shown that FS epithelial machining to form microchannels (MC) significantly enhances stromal Rf penetration, achieving concentrations equivalent to 50% of epithelial debridement. The purpose of this study was to assess the corneal wound healing response to MC-assisted UVA and NLO CXL in rabbits to determine their relative safety and efficacy.

Methods : Using a 1030nm FS laser with 5μJ pulse energy, the corneal epithelium of 36 rabbits were machined to create 2μm diameter by 25μm long MC at a density of 100 MC/mm². Eyes were then treated with 1% Rf solution for 30 minutes, rinsed with PBS and then underwent either UVA CXL following the standard Dresden protocol, or central 4mm NLO CXL. Rabbits were then followed at 2, 4, or 8 weeks post CXL and in vivo wound healing monitored by Lissamine green staining, OCT imaging, and Cochet Bonnet aesthesiometry. After sacrifice (3 males and 3 females/timepoint), corneas were removed and imaged for collagen autofluorescence (CAF) to verify efficacy of CXL, followed by immunohistochemistry (IHC) to analyze the cellular wound healing response.

Results : While rabbits treated with NLO CXL showed no epithelial damage, those receiving UVA CXL all showed epithelial defects after 24 hours, averaging 23.9 ± 5.6 mm² that healed by 72 hours. Rabbits receiving UVA CXL also showed a complete loss of corneal sensitivity after 24 hours, averaging 196.6 ± 8.7 mg needed to elicit a blink reflex compared to the control value of 72.9 ± 13.8 mg, while NLO CXL resulted in no loss of corneal sensitivity. OCT imaging after UVA CXL revealed consistent stromal damage with the presence of a clear demarcation line, while no detectible stromal damage was identified after NLO CXL. CAF verified that all corneas included in the study contained CXL, and IHC confirmed the in vivo imaging results.

Conclusions : MC NLO CXL completely avoids epithelial damage, loss of corneal sensitivity and shows dramatically reduced anterior stromal damage compared to MC UVA CXL. This suggests that MC NLO CXL can achieve a faster visual recovery without postoperative pain or risk of infection unlike MC UVA CXL.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.