Abstract
Purpose :
To study intrastromal oxygen (O2) dynamics during a novel transepithelial corneal collagen crosslinking (CXL) protocol (Casey protocol).
Methods :
Ex-vivo experiments on rabbit corneas were performed using three CXL protocols (Table 1). The Casey protocol is a transepithelial method that utilizes high-concentration riboflavin soak followed by saline rinse to achieve high stromal concentration and relatively low epithelial concentration. Moderate irradiance UV pulses with long off period allows for O2 replenishment in a high (>90%) ambient oxygen environment. The Casey protocol is compared to the standard epi-off Dresden protocol and a high-UV hyperoxic protocol that simulates the Avedro-Boost transepithelial protocol. Stromal O2 was measured with a fiberoptic oximeter at an approximate stromal depth of 180 µm (Table 1).
Results :
The stromal O2 time profile was averaged over experimental CXL with 6-minute UV exposure (Figure 1). The initial stromal O2 concentration %(±SD) for epi-off Dresden, Casey, and high-UV hyperoxic protocols were 17% (±0.1%), 65% (±1.1%), and 71% (±0.4%), respectively. After the UV was turned On, stromal O2 depleted rapidly over ~25 sec, 65 sec, and 37 sec to trough values of 4.5% (±1.2%), 27% (±7.4%), and 12% (±1.8%) for Dresden, Casey, and high-UV hyperoxic protocols, respectively. During the 8 sec UV-off periods in the Casey protocol, stromal O2 recovery of 11% was observed. No O2 recovery was observable over the 1 second UV-off period in the high-UV hyperoxic protocol, but a slow 11% recovery was noted over the 6-minute UV exposure
Conclusions :
Ambient O2 enrichment was effective in maintaining anterior stromal O2 during transepithelial CXL to a higher level compared to Dresden epi-off protocol. The Casey protocol further allowed for stromal O2 to recover to higher level during the longer 8-second UV-off period. Upward drift of stromal O2 over the 6-minute UV exposure was observed in the high-UV hyperoxic protocol, likely due to riboflavin depletion. The results suggest that the Casey CXL protocol allows for greater O2 penetration into the stroma and may allow for effective CXL reaction to occur over a greater range of stromal depth.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.