Comparison of two annular photorefractive intrastromal cross-linking protocols in high oxygen for low-grade myopia through 24-month follow-up

Abstract

Purpose: To compare two annular epithelium-on (epi-on) high oxygen photorefractive intrastromal cross-linking (PiXL) illuminations protocols for treatment of low-grade myopia. Methods: In this randomized, single-masked, intra-individually comparative study, healthy individuals with bilateral low-grade myopia (manifest refractive spherical equivalent (MRSE) −0.75 diopters (D) to −2.50 D) were treated with high oxygen epi-on PiXL. One eye was randomized to receive pulsed accelerated 365-nm ultraviolet-A illumination in a central annular zone of 4.0 mm (1 second on, 1 second off; 30 mW/cm2), and the fellow eye in a 3.5 mm annular zone (0.5 second on, 1 second off; 45 mW/cm2). Uncorrected distance visual acuity (UDVA), MRSE, low-contrast visual acuity (LCVA), best spectacle corrected visual acuity (BSCVA), endothelial cell count (ECC) and Scheimpflug light scattering depths were assessed through 24-month follow-up. Results: Twenty-seven participants (54 eyes) were included. The 3.5 mm protocol rendered less subjective ocular discomfort posttreatment and a larger improvement than the 4.0 mm protocol in UDVA: −0.52 (−0.72, −0.32) logMAR (medians and interquartile ranges, IQR) and −0.38 (−0.50, −0.22), p = 0.003 and MRSE: +1.25 D (0.75, 1.50) and +1.0 (0.75, 1.0), p = 0.037. The transient reduction in LCVA was larger with the 3.5 mm protocol (p < 0.01). No adverse events, and no reductions in ECC or BSCVA were noted. Conclusion: Epi-on PiXL in high oxygen reduces myopia in healthy eyes. A larger reduction of myopia and less early posttreatment subjective ocular discomfort can be seen with a smaller treatment zone, but likely at the expense of a transient decrease in low-contrast visual acuity.