Quantitative assessment of corneal biomechanical changes in vivo after photorefractive intrastromal corneal cross-linking using optical coherence elastography.

Background: Photorefractive intrastromal corneal cross-linking (PiXL) treatment corrects myopia by enhancing localized central corneal biomechanics. However, the dose-effect relationship between the changes in corneal biomechanics and alterations in corneal curvature resulting from this treatment remain unclear. We therefore developed an acoustic radiation force optical coherence elastography (ARF-OCE) technique to investigate the dose-effect relationship in PiXL.

Methods: ARF-OCE measurements and corneal topography were performed 3 days before and 1 week after PiXL treatment. Depth-resolved Young's modulus images of the in vivo corneas were obtained based on the phase velocity of the Lamb wave. PiXL treatments with five ultraviolet-A (UVA) energy doses (5.4, 15, 25, 35, and 45 J/cm²) were administered to rabbit corneas in vivo (n=15).

Results: The percentage change in Young's modulus (ΔE%) of the cornea increased from 0.26 to 1.71 as the UVA energy dose increased from group I (5.4 J/cm²) to group V (45 J/cm²). Meanwhile, the change in the mean keratometry (ΔK_m ) of the cornea increased from 0.40 to 2.10 diopters (D) as the UVA energy dose increased from group I to group IV (35 J/cm²). Furthermore, a statistically significant positive correlation was observed between ΔE% and ΔK_m in groups I to IV.

Conclusions: With increasing UVA energy dose, the corneal Young's modulus significantly increased. Given the observed correlation, ΔE% holds promise as a new quantitative biomechanical parameter for determining the dose-effect relationship in PiXL treatment. It should be emphasized that there may be an inflection point of ΔE%, at which corneal keratometry ceases to flatten and begins to increase. The ARF-OCE system has demonstrated its efficacy in quantitatively assessing changes in corneal biomechanics in vivo following PiXL treatment. This technique has great potential in facilitating the quantitative determination of the dose-effect relationship in PiXL treatment.