The Resistance of Riboflavin/UV-A Corneal Cross-Linking to Enzymatic Digestion Is Oxygen-Independent.

PURPOSE: Corneal cross-linking (CXL) with riboflavin and UV-A induces several effects in the cornea, including biomechanical stiffening, generation of reactive oxygen species, and increased resistance to enzymatic digestion. Whereas the biomechanical stiffening effect is oxygen-dependent, little is known about the effect of oxygen on the resistance to enzymatic digestion. Here, we examined CXL-induced enzymatic resistance in the absence of oxygen. METHODS: Ex vivo porcine corneas (n = 160) were assigned to 5 groups. Group 1 was the control group (abrasion and riboflavin application). Groups 2 and 3 received accelerated 10 and 15 J/cm2 high-fluence CXL protocols in the presence of oxygen (9'15″ @ 18 mW/cm2 and 8'20″ @ 30 mW/cm2, respectively), whereas groups 4 and 5 received accelerated 10 and 15 J/cm2 high-fluence CXL protocols in the absence of oxygen (oxygen content less than 0.1%). After CXL, corneas were digested in 0.3% collagenase A solution. Mean time until complete dissolution was determined. RESULTS: The mean times to digestion in groups 1 through 5 were 22.31 ± 1.97 hours, 30.78 ± 1.83 hours, 32.22 ± 2.22 hours, 31.38 ± 2.18 hours, and 31.69 ± 2.53 hours, respectively. Experimental CXL groups showed significantly higher (P < 0.001) resistance to digestion than nonirradiated controls. There was no significant difference in time to digestion across all experimental CXL groups, irrespective of fluence delivered or the absence of oxygen. CONCLUSIONS: The resistance to digestion in accelerated high-fluence riboflavin/UV-A CXL is oxygen-independent, which is of particular importance when developing future optimized CXL protocols for corneal ectasia and infectious keratitis.

Effect of accelerated high-fluence riboflavin and rose bengal-mediated corneal cross-linking on resistance to enzymatic digestion.

PURPOSE: This study evaluated the effect of high-fluence accelerated corneal cross-linking on the resistance to enzymatic digestion, assessing two chromophore/light combinations: riboflavin/UV-A light (RF/UV-A) and rose bengal/green light (RB/green). METHODS: Freshly prepared ex-vivo porcine corneas (n = 189) were divided into 8 groups groups. Group A corneas were unirradiated controls without chromophore soaking (A0), or soaked with riboflavin (A1) or rose bengal (A2). Group B corneas underwent accelerated epi-off RF/UV-A CXL at fluences of 5.4 J/cm² (B1), 10 J/cm² (B2), or 15 J/cm² (B3). Group C corneas underwent accelerated epi-off RB/green CXL at fluences of either 10 J/cm² (C1) or 15 J/cm² (C2). Following CXL, all corneas were digested in 0.3% collagenase-A solution, and the time until complete dissolution was measured. RESULTS: Non-irradiated controls exposed to RF and RB enhanced corneal resistance to collagenase digestion, with RB having a stronger effect than RF. RF/UV-A-treated corneas showed significantly increased digestion resistance with increasing fluence levels. RB/green-treated corneas displayed enhanced digestion resistance with each increase in fluence up to 10 J/cm²; a 15 J/cm² fluence yielded similar digestion resistance times to a 10 J/cm² fluence, suggesting a plateau effect in accelerated RB/green CXL protocols. CONCLUSIONS: When compared to standard-fluence treatments, high-fluence accelerated epi-off CXL using both riboflavin and rose bengal significantly increases resistance to enzymatic digestion. The optimal settings for clinical protocols might be 15 J/cm² (30 mW/cm² for 8 min 20 s) for RF/UV-A and 10 J/cm² (15 mW/cm² for 11 min 7 s) for RB/Green Light.

Combining Riboflavin/UV-A Light and Rose Bengal/Green Light Corneal Cross-Linking Increases the Resistance of Corneal Enzymatic Digestion.

Purpose: The purpose of this study was to determine if concurrent riboflavin/UV-A light (RF/UV-A) and rose Bengal/green light (RB/green) epi-off PACK-CXL enhances corneal resistance to enzymatic digestion compared to separate chromophore/light treatments. Methods: Ex vivo porcine corneas were allocated as follows. Group A corneas were soaked with riboflavin (RF) and were either not irradiated (A1, controls) or were irradiated with 10 (A2) or 15 J/cm² (A3) UV-A light at 365 nm, respectively. Group B corneas were soaked with RB and either not irradiated (B1, controls) or were illuminated with 10 (B2) or 15 J/cm² (B3) green light at 525 nm, respectively. Corneas in group C were soaked with both RF and RB and were either not irradiated (C1, controls) or were subjected to the same session consecutive 10 J/cm2 (C2) or 15 J/cm2 (C3) UV-A and green light exposure. Following treatment, all corneas were exposed to 0.3% collagenase A to assess digestion time until corneal button dissolution. Results: A1 to A3 digestion times were 21.38, 30.5, and 32.25 hours, respectively, with A2 and A3 showing increased resistance to A1. B1-3 had digestion times of 31.2, 33.81, and 34.38 hours, with B3 resisting more than B1. C1 to C3 times were 33.47, 39.81, and 51.94 hours; C3 exhibited superior resistance to C1 and C2 (both P < 0.05). Conclusions: Same-session combined RF/UV-A and RB/green PACK-cross-linking significantly increases corneal enzymatic digestion resistance over standalone treatments. Translational Relevance: Combining RF-based and RB-based PACK-CXL considerably increases corneal collagenase digestion resistance, potentially minimizing ulcer size in clinical contexts.

High-Fluence Accelerated PACK-CXL for Bacterial Keratitis Using Riboflavin/UV-A or Rose Bengal/Green in the Ex Vivo Porcine Cornea.

Purpose: To investigate and compare the efficacy of high-fluence accelerated photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) using either riboflavin/ultraviolet (UV)-A light or rose bengal/green light to treat Staphylococcus aureus or Pseudomonas aeruginosa infections in an ex vivo porcine cornea model. Methods: One hundred and seventeen ex vivo porcine corneas were injected with clinical isolates of S. aureus or P. aeruginosa, divided into eight groups, and cultured for 24 hours. Then, either riboflavin with UV-A light irradiation (30 mW/cm2; 8 minutes, 20 seconds; 15 J/cm2) or rose bengal with green light irradiation (15 mW/cm2, 16 minutes, 40 seconds; 15 J/cm2) was applied; unirradiated infected groups served as controls. All corneas were incubated for another 24 hours. Next, corneal buttons were obtained and vortexed to release the bacterial cells. The irradiated and unirradiated solutions were then plated and incubated on agar plates. The amount of colony-forming units was quantified and the bacterial killing ratios (BKRs) resulting from different PACK-CXL protocols relative to non-treated controls were calculated. Results: Riboflavin/UV-A light PACK-CXL resulted in median BKRs of 52.8% and 45.8% in S. aureus and P. aeruginosa, respectively, whereas rose bengal/green light PACK-CXL resulted in significantly greater BKRs of 76.7% and 81.0%, respectively (both P < 0.01). Conclusions: Both accelerated PACK-CXL protocols significantly decreased S. aureus and P. aeruginosa bacterial loads. Comparing the riboflavin/UV-A light and rose bengal/green light PACK-CXL approaches in the same experimental setup may help develop strain-specific and depth-dependent PACK-CXL approaches that could be used alongside the current standard of care. Translational Relevance: Our study used an animal model to gain insight into the efficacy of high-fluence accelerated PACK-CXL using either riboflavin/UV-A light or rose bengal/green light to treat Staphylococcus aureus or Pseudomonas aeruginosa infections.

Rates of infectious keratitis and other ocular surface adverse events in corneal cross-linking for keratoconus and corneal ectasias performed in an office-based setting: a retrospective cohort study.

BACKGROUND: This study aimed to compare the complication rates of epithelium-off corneal cross-linking (epi-off CXL) performed in an office-based setting with those of epi-off CXL performed in an operating room. METHODS: A retrospective cohort study, comprising 501 consecutive epi-off CXL procedures, performed in a non-sterile procedure room without laminar flow ventilation at the ELZA Institute in Zurich, Switzerland, between November 2015 and October 2021, was conducted. RESULTS: No cases of postoperative infectious keratitis were observed, while sterile infiltrates occurred in 10 out of 501 (2.00%) patients, all of whom responded well to topical steroid therapy. Delayed epithelialization (> 7 days) occurred in 14 out of 501 (2.79%) patients. No other adverse events were noted. CONCLUSIONS: Office-based epi-off CXL does not appear to be associated with an increased risk of complications when compared to operating room settings.

Corneal crosslinking with riboflavin using sunlight.

PURPOSE: To assess whether sunlight might be used to induce a biomechanical stiffening effect in riboflavin-soaked corneas similar to the effect observed in corneal crosslinking (CXL) using riboflavin and UV-A light. SETTING: Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland. DESIGN: Experimental study. METHODS: 52 porcine eyes were assayed. The concentration of riboflavin in the corneal stroma was estimated using UV-A transmission in a preliminary experiment. Then, the duration of sunlight exposure to achieve a fluence of 7.2/cm 2 was calculated. Finally, de-epithelialized corneas were divided equally into 3 groups and soaked with riboflavin 0.1% (control group and Group 1) or 0.5% (Group 2). Eyes from Groups 1 and 2 were then exposed to sunlight. The elastic modulus was calculated as an indicator of stiffness. RESULTS: Riboflavin concentration in Group B was higher by a factor of 2.8 than Group A. According to live illuminance measurements and stromal riboflavin concentration, the sunlight exposure duration varied between 16 minutes and 45 minutes. Groups 1 and 2 had higher elastic modulus than controls ( P < .0001) but did not differ between them ( P = .194). The stiffening effect was 84% and 55%, respectively. CONCLUSIONS: Sunlight exposure of ex vivo corneas soaked in both riboflavin 0.1% and 0.5% resulted in increased corneal stiffness. Specifically, riboflavin 0.1% with longer UV-A exposure showed a trend for a greater stiffening effect, which might open new alleys for the use of oral riboflavin and fractioned sunlight exposure as less invasive CXL techniques.

Expanding indications for corneal cross-linking.

PURPOSE OF REVIEW: The aim of this study was to summarize the recent developments in corneal cross-linking (CXL) and its indications, including corneal ectasias, refractive surgery and infectious keratitis. RECENT FINDINGS: Advances in CXL technology, such as the use of higher-intensity LED ultraviolet (UV) light sources and a better understanding of the UV-riboflavin photochemical reaction, have enabled safer and more effective methods of cross-linking thin and ultra-thin corneas, and more effective accelerated transepithelial/'epi-on' CXL procedures that are beginning to supplant the Dresden protocol as the 'gold standard' CXL method. CXL is also being used in combination with laser surgery, not only to expand the patient base who can receive refractive surgery, but also to help rehabilitate vision in patients with ectasia. CXL, and CXL combined with photorefractive keratectomy (PRK), can result in corneal flattening of 1-2 D, and corneal regularization of 4-5 D, respectively. Finally, photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) has been shown to be an effective therapy for infectious keratitis, both alone, and in combination with antimicrobial drugs. SUMMARY: CXL has evolved from a single technique to treat a single corneal ectasia, keratoconus, to several techniques with several indications, spanning a spectrum of corneal ectasias, as well as visual rehabilitation, refractive procedures and infectious keratitis treatment.

Progressive keratoconus in patients older than 48 years.

PURPOSE: To report cases of progressive keratoconus (KC) in patients aged ≥48 years and the successful arrest of progression using corneal cross-linking (CXL) with riboflavin and ultraviolet-A light. OBSERVATIONS: Five eyes from four patients with progressive KC aged 48, 48, 51 and 54 years are reported in this case series. All eyes were followed regularly after initial diagnosis. Kmax was used as an indicator of progression and KC progressed at a rate of 1.4 diopters in 6 months and 14.6 diopters in 14 months. All patients eventually received CXL, and all were aged ≥50 years at the time of the procedure. One eye required two CXL procedures to successfully stabilize the patient's cornea. CONCLUSION: Despite the probability of KC progression strongly declining after the age of 40 years, it never becomes zero. It is therefore advisable to continue regular follow-up corneal tomography examinations in patients with KC, even in their fifth and sixth decades of life.

Demarcation Line Depth in Epithelium-Off Corneal Cross-Linking Performed at the Slit Lamp.

We aimed to evaluate the depth of the demarcation line following accelerated epithelium-off corneal cross-linking (A-CXL) performed at the slit lamp with the patient sitting in an upright position. Twenty-three eyes from twenty patients, undergoing epi-off A-CXL (9 mW/cm2 for 10 min) using a CXL device at the slit lamp in the upright position. Demarcation line depth was assessed at 1 month after the procedure using anterior segment optical coherence tomography (AS-OCT) and specialized software. Surgery was uneventful in all cases. The average postoperative demarcation line depth achieved was 189.4 µm (standard deviation: 58.67 µm). The demarcation line depth achieved with patients sitting upright, receiving CXL at the slit lamp, is similar to published data on CXL performed in the supine position, suggesting that demarcation line depth is not dependent on patient orientation during CXL.

The Impact of Repetitive and Prolonged Eye Rubbing on Corneal Biomechanics.

PURPOSE: To evaluate the effect of simulated repetitive eye rubbing on the corneal biomechanics of porcine eyes using an ex vivo model system. METHODS: The average rubbing force that patients with keratoconus apply to their eyelids was previously determined. Fresh porcine eyes with eyelids were either exposed to 10,500 rub cycles from a custom-built eye rubbing machine that rubbed with a similar force to knuckle human eye rubbing (n = 33) or no rubbing at all (control; n = 37). A total of 10,500 rubs are equivalent to 1 year of rubbing six times daily, five movements per rub. The corneal biomechanical properties of these eyes were then tested by measuring the elastic modulus of 5-mm strips. RESULTS: The elastic modulus at the range of 1% and 5% of strain was 1.219 ± 0.284 and 1.218 ± 0.304 N/mm2 in the eye rubbing group and the no-rub control group, respectively. Corneal stiffness was similar in both groups (P = .984). CONCLUSIONS: The threshold to induce biomechanical changes (purely by eye rubbing) must be higher than 10,500 rubbing movements, suggesting that occasional eye rubbing may not affect corneal biomechanics in normal eyes, and likely only triggers keratoconus progression in predisposed corneas. Further in vivo studies assessing the impact eye rubbing has on inflammatory activity and the biomechanical properties of weakened corneas is warranted. [J Refract Surg. 2022;38(9):610-616.].

Repeated application of riboflavin during corneal cross-linking does not improve the biomechanical stiffening effect ex vivo.

PURPOSE: To evaluate whether repeated application of riboflavin during corneal cross-linking (CXL) has an impact on the corneal biomechanical strength in ex-vivo porcine corneas. DESIGN: Laboratory investigation. METHODS: Sixty-six porcine corneas with intact epithelium were divided into three groups and analyzed. All corneas were pre-soaked with an iso-osmolar solution of 0.1% riboflavin in a phosphate-buffered saline (PBS) solution ("riboflavin solution"). Then, the corneas in Groups 1 and 2 were irradiated with a standard epi-off CXL (S-CXL) UV-A irradiation protocol (3 mW/cm2 for 30 min); while the corneas in Group 3 were not irradiated and served as control. During irradiation, Group 1 (CXL-PBS-Ribo) received repeated riboflavin solution application while corneas in Group 2 (CXL-PBS) received only repeated iso-osmolar PBS solution. Immediately after the procedure, 5-mm wide corneal strips were prepared, and elastic modulus was calculated to characterize biomechanical properties. RESULTS: Significant differences in stress-strain extensiometry were found between two cross-linked groups with control group (P = 0.005 and 0.002, respectively). No significant difference was observed in the normalized stiffening effect between Groups 1 and 2 (P = 0.715). CONCLUSIONS: The repeated application of riboflavin solution during UV-A irradiation does not affect the corneal biomechanical properties achieved with standard epi-off CXL. Riboflavin application during CXL may be omitted without altering the biomechanical stiffening induced by the procedure.

A New Postoperative Regimen after CXL and PRK Using Topical NSAID and Steroids on the Open Ocular Surface.

Corneal epithelium removal during photorefractive keratotomy (PRK), TransPRK, or corneal cross-linking (CXL) means that patients experience pain and inflammation after the procedure, which need to be carefully managed with topical drug regimens. One highly effective class of topical analgesics is non-steroidal anti-inflammatory drugs (NSAIDs), but these must be used carefully, as their use has been associated with delayed re-epithelialization and, in rare cases, corneal melting. However, our clinical experience has been that the concomitant use of topical corticosteroids obviates this risk. Here, we present a mechanistic explanation for our observations, our TransPRK and epithelium-off CXL protocols, and the postoperative medication regimens where topical NSAIDs are used in combination with topical steroid therapy during the first two postoperative days (where pain and inflammation levels are the highest). We detail the results of a single-center retrospective case analysis that examined eyes that underwent TransPRK (n = 301) or epithelium-off CXL (n = 576). Topical NSAID use in the first two postoperative days to control pain and inflammation after PRK/TransPRK or epithelium-off CXL, when used in combination with topical steroid therapy, does not appear to be associated with corneal melting or delayed epithelial healing. This approach may represent an improvement over current methods of handling post-surgical pain in procedures that require corneal epithelial debridement.

Repeated High-Fluence Accelerated Slitlamp-Based Photoactivated Chromophore for Keratitis Corneal Cross-Linking for Treatment-Resistant Fungal Keratitis.

PURPOSE: The purpose of this study was to report a case of fungal keratitis resistant to standard-of-care antimicrobial treatment and successful resolution, thanks to the repeated high-fluence accelerated photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL). METHODS: This was a case report. RESULTS: A 79-year-old male patient with previous Descemet membrane endothelial keratoplasty presented with a corneal ulcer that was resistant to topical antimicrobial therapy and amniotic membrane placement. Fungal keratitis was diagnosed, and the cornea was on the verge of perforation. After over a month of topical and systemic therapy without marked improvement, the patient underwent 2 repeated high-fluence accelerated CXL procedures (7.2 J/cm2 using a UV irradiation of 30 mW/cm2 for 4 minutes) over an interval of 8 days (accumulated fluence of 14.4 J/cm2), which resulted in significant clinical improvement, with consolidation into a quiescent scar. CONCLUSIONS: PACK-CXL protocols delivering a total UV fluence of 5.4 J/cm2 (as per the original Dresden protocol for corneal ectasia cross-linking) can be an effective primary therapy for initial or superficial corneal infections because approximately half of the energy is absorbed in the first 100 µm of a riboflavin-soaked cornea. However, fungal keratitis may require higher fluences than 5.4 J/cm2 because, unlike ectatic corneas, corneal ulcers are not transparent, and the infection may involve deep stroma. This case illustrates how repeated high-fluence accelerated PACK-CXL can be used to successfully treat fungal keratitis resistant to conventional topical and systemic medications.

Combining Spectral-Domain OCT and Air-Puff Tonometry Analysis to Diagnose Keratoconus.

PURPOSE: To investigate the diagnostic capacity of spectral-domain optical coherence tomography (SD-OCT) combined with air-puff tonometry using artificial intelligence (AI) in differentiating between normal and keratoconic eyes. METHODS: Patients who had either undergone uneventful laser vision correction with at least 3 years of stable follow-up or those who had forme fruste keratoconus (FFKC), early keratoconus (EKC), or advanced keratoconus (AKC) were included. SD-OCT and biomechanical information from air-puff tonometry was divided into training and validation sets. AI models based on random forest or neural networks were trained to distinguish eyes with FFKC from normal eyes. Model accuracy was independently tested in eyes with FFKC and normal eyes. Receiver operating characteristic (ROC) curves were generated to determine area under the curve (AUC), sensitivity, and specificity values. RESULTS: A total of 223 normal eyes from 223 patients, 69 FFKC eyes from 69 patients, 72 EKC eyes from 72 patients, and 258 AKC eyes from 258 patients were included. The top AUC ROC values (normal eyes compared with AKC and EKC) were Pentacam Random Forest Index (AUC = 0.985 and 0.958), Tomographic and Biomechanical Index (AUC = 0.983 and 0.925), and Belin-Ambrósio Enhanced Ectasia Total Deviation Index (AUC = 0.981 and 0.922). When SD-OCT and air-puff tonometry data were combined, the random forest AI model provided the highest accuracy with 99% AUC for FFKC (75% sensitivity; 94.74% specificity). CONCLUSIONS: Currently, AI parameters accurately diagnose AKC and EKC, but have a limited ability to diagnose FFKC. AI-assisted diagnostic technology that uses both SD-OCT and air-puff tonometry may overcome this limitation, leading to improved treatment of patients with keratoconus. [J Refract Surg. 2022;38(6):374-380.].

Repeatability of a Scheimpflug tonometer to measure biomechanical parameters before and after myopic refractive surgery.

PURPOSE: To assess the repeatability of several corneal biomechanical parameters with a Scheimpflug tonometer (Corvis ST) in myopic eyes and eyes that underwent transepithelial photorefractive keratectomy (transPRK), small-incision lenticule extraction (SMILE), or femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. SETTING: Eye Hospital of Wenzhou Medical University, Wenzhou, China. DESIGN: Prospective randomized controlled study. METHODS: 315 eyes from 315 patients (135 myopes, 58 post-transPRK, 52 post-SMILE, and 70 post-FS-LASIK) were included. 3 consecutive scans were performed to evaluate the repeatability of the 40 parameters examined. RESULTS: 315 eyes were included. In all eyes, the coefficient of variation (CoV) for intraocular pressure (IOP) and biomechanical-corrected IOP (bIOP) ranged from 7.29% to 9.47% and 6.11% to 7.75%, respectively; the CoV of pachymetry was <0.8%. The intraclass correlation coefficient of Corvis Biomechanical Index-Laser Vision Correction (LVC) was 0.680 for post-transPRK, 0.978 for post-SMILE, and 0.911 for post-FS-LASIK. The CoV of Stress-Strain Index (SSI) was 204.93% for post-transPRK, 91.92% for post-SMILE, and 171.72% for post-FS-LASIK. The CoV of the 6 clinically important dynamic corneal response parameters ranged from 2.0% to 7.8% for myopia, 1.8% to 11.1% for post-transPRK, 2.1% to 8.7% for post-SMILE, and 1.8% to 8.8% for post-FS-LASIK. CONCLUSIONS: Excellent intrameasurement repeatability of IOP, bIOP, and pachymetry was observed in all groups; SSI measurement in post-LVC corneas displayed more variation. Caution is warranted when assessing SSI in post-LVC corneas for the purpose of diagnosing iatrogenic ectasia or evaluating biomechanical remodeling of postoperative refractive corneas.

High-Fluence Accelerated Epithelium-Off Corneal Cross-Linking Protocol Provides Dresden Protocol-Like Corneal Strengthening.

Purpose: To assess whether optimized technical settings for accelerated epithelium-off corneal cross-linking may lead to increases in biomechanical stiffness similar to the benchmark 30-minute epithelium-off Dresden protocol. Methods: Three-hundred porcine eyes were divided equally into six groups for analysis. All samples underwent epithelial debridement and soaking with 0.1% iso-osmolar riboflavin solution for 20 minutes. Corneal cross-linking (CXL) was performed using epithelium-off protocols varying in acceleration and total fluence (intensity in mW/cm² * time in minutes, total fluence in J/cm²): standard (S)-CXL (3*30, 5.4), accelerated (A)-CXL (9*10, 5.4), A-CXL (9*13'20″, 7.2), A-CXL (18*6'40″, 7.2), and A-CXL (18*9'15″, 10). Control corneas were not irradiated. The elastic modulus of 5-mm wide corneal strips was measured as an indicator of corneal stiffness. Results: All irradiated groups had significantly higher elastic modulus than controls (P < 0.05), with a stiffening effect of 133% S-CXL (3*30, 5.4), 122% A-CXL (9*10, 5.4), 120% A-CXL (9*13'20″, 7.2), 114% A-CXL (18*6'40″, 7.2) and 149% A-CXL (18*9'15″, 10). The high-fluence accelerated epithelium-off protocol (18*9'15″, 10) showed the highest stiffening effect. Elastic modulus at 5% strain (1%-5% strain) showed significant differences between A-CXL (18*9'15″, 7.2) and three other accelerated protocols: A-CXL (9*10, 5.4; P = 0.01), A-CXL (9*13'20″, 7.2; P = 0.003), and A-CXL (18*6'40″, 10; P = 0.0001). Conclusions: An accelerated high-fluence epithelium-off CXL protocol (18 mW/cm² for 9'15″) was identified to provide a significantly greater stiffening effect than any other accelerated protocols and is indistinguishable from the Dresden protocol, with accelerating irradiation times ranging from 30 to 9 minutes; by combining gentle acceleration with higher fluence, such a protocol does not require supplemental oxygen. Translational Relevance: This A-CXL (18*9'15″, 10) protocol has the potential to become a new standard in epithelium-off CXL, delivering Dresden protocol-like strengthening over a shorter period.