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) À0.75 diopters (D) to À2.50 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: À0.52 (À0.72, À0.32) logMAR (medians and interquartile ranges, IQR) and À0.38 (À0.50, À0.22), 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.

Transepithelial Enhanced Fluence Pulsed Light M Accelerated Crosslinking for Early Progressive Keratoconus with Chemically Enhanced Riboflavin Solutions and Air Room Oxygen

“…On the other hand, we have recently demonstrated that by using 30 mW/cm 2 UV power with a shorter exposure time, the intraoperative oxygen supplementation enhances the aerobic pathway of CXL, increasing the treatment penetration and corneal flattening [ 20 ]⁠. In this case, the 18 mW/cm 2 UV-A power and the longer exposure time optimizes the CXL kinetic, avoiding the necessity of supplementary intraoperative oxygen that is recommended with 30 mW trans-epithelial customized ACXL protocols [ 20 ]; in fact, the protocols being equal, the use of supplementary oxygen was found to also give the treatment some refractive power by increasing the flattening of the treated cornea [ 22 , 23 , 24 , 25 ].…”

“…Indeed, the Type-II CXL is strictly oxygen mediated and its efficacy is proportional to the light dose and oxygen and intra-stromal riboflavin concentration, while the Type-I CXL effect is mainly related to the treatment energy dose and riboflavin concentration gradient, which must be higher and well-distributed in about 200 µm of the corneal stroma, allowing for direct coupling with the collagen substrate [ 27 ]. These mixed physio-chemical reactions may explain the efficacy of the new transepithelial treatments with increased fluence, higher riboflavin concentration solutions, and pulsed-light [ 19 , 23 , 25 ]. Higher fluence (10 J/cm 2 ) and chemically boosted or enhanced riboflavin solutions further increase the efficiency of trans-epithelial CXL in a low oxygen environment and anaerobic conditions.…”

Randomized Clinical Trial Comparing Customized Corneal Crosslinking: Epi-on in High Oxygen and Epi-off in Room Air for Keratoconus

“…Accordingly, studies evaluating supplemental oxygen during the illumination have shown promising results both in KC and in low-grade myopia. [9][10][11][12][13] Customized topography-guided CXL means more intense treatment of the thinnest, most stress-loaded cone area. 14 This has been shown in silico to potentially halt the biomechanical decompensation cascade, which increases the corneal curvature to compensate for the uneven stress distribution in the cornea.…”

“…Accordingly, studies evaluating supplemental oxygen during the illumination have shown promising results both in KC and in low-grade myopia. 9–13…”