Epithelium-on photorefractive intrastromal cross-linking (PiXL) for reduction of low myopia

To report the 9-12-month outcomes of a novel procedure for reduction of low myopia through epithelium-on photorefractive intrastromal cross-linking (PiXL) with customized control of topographic distribution of ultraviolet (UV)-fluence.

Myopic patients with normal (non-ectatic) corneas underwent the PiXL procedure for reduction of low myopia. PiXL treatments were delivered through selective application of UVA light based on the refractive error of each patient. Clinical evaluation included safety (corrected distance visual acuity, endothelial cell count, central corneal thickness, anterior ocular health) and efficacy (uncorrected distance visual acuity, manifest refraction, K-mean) examinations. In addition, a patient satisfaction survey was conducted at 9 months post-procedure to evaluate patients' subjective experience with the procedure.

Fourteen myopic eyes (mean manifest refraction spherical equivalent -1.62±0.6D; range -0.75 to -2.65D) of 8 subjects (mean age 30 years old; range 24-51 years old) were enrolled in the study. At 12 months post-procedure, a mean manifest refraction spherical equivalent reduction of 0.72±0.43D (P<0.001) was observed, with a corresponding gain in uncorrected visual acuity of 0.25 logMAR and mean K-mean flattening of 0.47±0.46D. All patients achieved best corrected visual acuity of 20/20 or better from 1 month onward. There were no cases of ocular infection or secondary changes to the crystalline lens and retina due to UV exposure, while transient corneal haze subsided gradually.

The epithelium-on PiXL procedure was safe and effective in reducing myopic refractive error in this study with up to 12 months follow-up. Early results of this novel application of collagen cross-linking are encouraging but longer-term data in larger studies are required.

This paper serves to introduce and report the early clinical results of epithelium-on PiXL, a novel application of cornea cross-linking, in reducing low myopia in Asian eyes, which are under-represented in studies of similar design.