Comparison of two annular photorefractive intrastromal cross‐linking protocols in high oxygen for low‐grade myopia through 24‐month follow‐up. Issue 5 (5th October 2021) - Näslund, Sofie
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/cm 2 ), and the fellow eye in a 3.5 mm annular zone (0.5 second on, 1 second off; 45 mW/cm 2 ). 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.