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/cm) were administered to rabbit corneas (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/cm) to group V (45 J/cm). Meanwhile, the change in the mean keratometry (Δ ) 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/cm). Furthermore, a statistically significant positive correlation was observed between ΔE% and Δ 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 following PiXL treatment. This technique has great potential in facilitating the quantitative determination of the dose-effect relationship in PiXL treatment.