Purpose: To compare transepithelial (TE) photorefractive intrastromal corneal cross-linking (PiXL) and photorefractive keratectomy (PRK) in low myopia. Setting: Monocentric study conducted in France (Purpan Hospital, Toulouse) Design: Prospective, intraindividual ethics committee-approved, comparative nonrandomized study. Methods: Myopic patients with manifest refraction spherical equivalent (MRSE) of -1.00 to -2.50 diopters (D), and cylindrical component plano to -0.75 D were included. Dominant eye underwent PRK, and non-dominant eye TE-PiXL procedure with riboflavin (Paracel ® Part 1 & 2, Avedro Inc., Waltham, MS, USA), 30 mW/cm 2 pulsed UVA irradiation centered on pupil (Mosaic™ System,Avedro Inc., Waltham, MS, USA) for 16 minutes and 40 seconds and supplemental oxygen delivery mask. The primary outcome measure was the change in MRSE. Other outcome measures were uncorrected and corrected distance visual acuity (UDVA and CDVA), mean keratometry (Km), and endothelial cell count (ECC) with a 6month follow-up. Adverse events were also assessed. Results: Nineteen patients were included. At 6 months, mean MRSE decreased by 0.72 ± 0.42 D in TE-PiXL eyes and by 1.35 ± 0.46 D in PRK eyes (P <.001). The mean change in UDVA was -0.35 ± 0.21 LogMAR in TE-PiXL eyes and -0.66 ± 0.19 LogMAR in PRK eyes (P <.001). No complications were reported. ECC and CDVA were statistically unchanged. Conclusion: PRK provided better visual and refractive outcomes than TE-PiXL. TE-PiXL however demonstrated the potential refractive effect of corneal cross-linking but with a limited magnitude of myopic correction to this point.

PURPOSE: To evaluate the efficacy and safety of transepithelial corneal cross-linking (CXL) with supplemental oxygen. METHODS: This was a prospective, non-comparative, pilot cohort study conducted at the National Reference Center for Keratoconus (Toulouse, France) on patients with progressive keratoconus. Transepithelial, pulsed, accelerated CXL was performed in an oxygen-rich atmosphere. Oxygen goggles were applied to the eyes to maintain a high level of oxygen during treatment. The main efficacy outcome was the mean change from baseline in maximum keratometry (Kmax) and the secondary outcomes were the mean changes in flat keratometry (K1), steep keratometry (K2), mean keratometry (Km), corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), and demarcation line depth. The safety outcomes were the incidence of adverse events, the mean change in pachymetry, and endothelial cell count. RESULTS: Thirty-four eyes of 34 patients were included. At 12 months postoperatively, the Kmax decreased by 1.56 ± 1.71 diopters (D) ( P < .0001) and CDVA improved by 0.093 ± 0.193 logMAR ( P < .02). The K2 and Km decreased by 0.51 ± 1.03 D ( P < .02) and 0.40 ± 0.78 D ( P < .01), respectively. There was no change in K1 and UDVA. The most frequent adverse event was corneal haze (64.78%). There were neither cases of infectious keratitis or loss of more than two lines in CDVA nor changes in pachymetry or endothelial cell count. CONCLUSIONS: Transepithelial CXL performed in an oxygen-rich atmosphere results in improved Kmax and CDVA with good safety. These promising findings suggest that this procedure could be safe and capable of halting the progression of keratoconus. [ J Refract Surg . 2021;37(1):42–48.]

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Corneal collagen crosslinking (CXL) is usually practiced on keratoconic corneas to strengthen the corneal biomechanical structure. The conventional CXL procedure, with riboflavin and ultraviolet A (UVA), initially involves corneal de-epithelialization to allow riboflavin penetration into the stroma. Discomfort and complications are related to this corneal debridement. Thus, transepithelial CXL has emerged to substitute for the conventional method. This technique preserves the epithelium and tends to ensure the same efficiency of corneal stiffening. To allow riboflavin penetration through the epithelial barrier, several chemical modifications to riboflavin, such as addition of enhancers (EDTA, benzalkonium chloride or 20% alcohol), and osmolar modifications have been applied. The most studied transepithelial riboflavin is Ricrolin TE ® , which combines two enhancers: amino alcohol and EDTA. The results of clinical studies have not demonstrated effectiveness yet. Moreover, the iontophoresis technique, a noninvasive procedure during which a low-intensity electric current is applied to enhance the penetration of riboflavin into the stroma, stands out as being as efficient as conventional application of riboflavin, based on a pre-clinical study. Another area of improvement of CXL is modification of the UVA irradiation profile or shortening of the UVA irradiation time while increasing the irradiation power. A longer follow-up and more investigations are still necessary to define the future of transepithelial CXL, but it is an exciting and rapidly evolving area.