Non-invasive assessment of the axial hydration gradient after corneal abrasion of the rabbit eye

Purpose. The lack of assessment and thus control of the hydration of the ablation site, is believed to he the cause of several undesired side-effects associated with cornea ablation. The aim of (his study was to quantify in-vivo the water distribution across the rabbit cornea as function of time after abrasion. Methods. A non-invasive scanning confocal Raman spectroscopy (SCRS) technique (25 mW Argon, Is probing time, SPKX500M, axial resolution 50 um) was used to assess the water content (Raman intensity ratio of water-peak/protein-peak) of consecutive layers along the optical axis of the cornea with scan-steps of 50 HID. Two regions were studied closely: the superficial 100 Jim (A) and the most posterior UK) u.m (P) of stroma. This technique was validated and calibrated in 9 m-vitro rabhil eyes, by quantifying the relationship between pachymetric- and SCRSassessed total corncal hydration (H). Eight corneas of NZW rabbits were abraded in-vivo, and the time dependenf changes in hydration were assessed for H, A and P. Results. Calibration revealed a linear relationship between pachyinelric- and SCRS-assessed H, invitrti (SI>=0.01, R-=0.94) as well as in-vivo before abrasion (SI)=0.10, R3=0.77). In agreement with current literature, H, A and P show different non-linear time-dependencies after abrasion. A correlated better with H than P <A=[0.72±0.()8]/J. R2=0.88. and /'=| 1.56±0.i 1 ]//, R:=<>.68), while the linear correlation between pachymetric- and SCRSassessed H after abrasion was reasonable (SD=().l 1, R2=0.87). Conclusion. Our results suggest that SCRS can be used to quantify the expected time-dependent changes of the axial corneal hydration gradient after abrasion m-vivo. This may render future applications of this technique possible in the assessment and control of corneal hydration.