Photorefractive intrastromal corneal crosslinking for treatment of low myopia: clinical outcomes using the transepithelial approach with supplemental oxygen

Abstract

Purpose: To evaluate the safety and efficacy of photorefractive intrastromal corneal crosslinking (PiXL) for the treatment of low myopia using the epithelium-on approach with supplemental oxygen. Setting: The Eye Foundation, Coimbatore, India. Design: Prospective interventional case series. Methods: Myopic nonectatic eyes underwent PiXL using the Mosaic system. Ultraviolet-A (UV-A) irradiation of 365 nm wavelength was delivered in an accelerated (30 mW/cm2) pulsed approach to provide a total fluence of 15 J/cm2. Supplemental oxygen (concentration greater than 95%) was provided to increase the efficacy of the epithelium-on approach during the UV-A irradiation. Efficacy was determined by improvement in mean refractive spherical equivalent (MRSE), uncorrected distance visual acuity (UDVA), and keratometric flattening. Safety was determined by loss of lines of corrected distance visual acuity, endothelial cell loss, and adverse events. Results: Fifty eyes of 26 patients with a mean age of 22.73 ± 3.74 years were included. A significant improvement in UDVA from baseline (logarithm of the minimum angle of resolution [logMAR] 0.63 ± 0.25) was noted at the 3-month (logMAR 0.08 ± 0.15) and 6-month (logMAR 0.13 ± 0.18) follow-up visits (P < .001). Significant keratometric flattening from baseline was noted at all follow-up visits (P < .001). No significant endothelial cell loss or adverse effects were noted. A significant correlation was noted between the change in MRSE and preoperative corneal biomechanics (deformation amplitude ratio, P = .029). Conclusions: Transepithelial PiXL with supplemental oxygen might be a safe and effective approach for reduction of myopia. The change in MRSE and keratometric flattening was greater in comparison with earlier protocols, including the epithelium-off approach.

Treatment effect with 2 photorefractive intrastromal cross‐linking protocols in low‐grade myopia through 24‐month follow‐up

“…Supplemental oxygen maintaining a hyperoxic environment in the corneal stroma counteracts oxygen depletion and enhances the reaction further (Hill et al 2019). In the current study, we demonstrated significant improvements in the visual acuity and refraction with stable results up to 24 months, which strengthens previous findings that epi‐on PiXL with high oxygen supply can be used for reduction of low‐grade myopia (Fredriksson et al 2019; El Hout et al 2019; Sachdev et al 2020).…”

“…Epi‐on PiXL in high oxygen is a novel therapeutic procedure that reshapes the corneal stroma without the need for epithelial debridement or stromal removal (Lim et al 2017; Fredriksson et al 2019; El Hout et al 2019; Sachdev et al 2020). Epi‐on techniques are beneficial with potentially less postoperative ocular discomfort, faster recovery for the patient and lower risks for serious complications such as postoperative infections and corneal scarring (Meek & Hayes 2013; Stulting et al 2018).…”

“…However, an intact epithelium limits the delivery of Riboflavin, UV‐A and oxygen to the corneal stroma, which is crucial for the cross‐linking reaction. To avoid hampering of the treatment effect, high‐irradiance UV‐A and chemical enhancers facilitating epithelium penetration have previously proven successful (Lim et al 2017; Stulting et al 2018; Fredriksson et al 2019; El Hout et al 2019; Sachdev et al 2020). Supplemental oxygen maintaining a hyperoxic environment in the corneal stroma counteracts oxygen depletion and enhances the reaction further (Hill et al 2019).…”

“…A modified variant of CXL, photorefractive intrastromal collagen cross‐linking (PiXL) has been introduced to deliver customized energy patterns to re‐model and flatten the corneal curvature in a controlled manner (Kanellopoulos 2014; Nordstrom et al 2017). By illuminating the central part of the cornea, the flattening effect has been shown by us and others to reduce or eliminate low‐grade myopia in healthy eyes (Kanellopoulos 2014; Elling et al 2017; Lim et al 2017; Elling et al 2018; Fredriksson et al 2019; El Hout et al 2019; Sachdev et al 2020). The impression from our previous studies is that an initial postoperative central haze could slow the post‐treatment improvement in visual acuity after such treatments (Beckman Rehnman et al 2014; Nordstrom et al 2017).…”

“…However, if available, oxygen from the ambient air reacts with the excited photosensitizer to form reactive oxygen species such as singlet oxygen and superoxide radicals, inducing collagen cross‐linking bonds in a type 2 reaction (Muller et al 2020). Thus, CXL causes biomechanical stiffening and stromal stabilization (Raiskup & Spoerl 2013), but the treatment also alters the corneal shape with a flattening of the corneal curvature (Meek & Hayes 2013), an effect that could potentially be used as a refractive treatment for myopia (Elling et al 2017; Lim et al 2017; Elling et al 2018; Fredriksson et al 2019; El Hout et al 2019; Sachdev et al 2020).…”