Corneal Cross-linking at the Slit Lamp.

PURPOSE: To describe a new surgical technique where corneal cross-linking (CXL) (to treat corneal ectasias) and photo-activated chromophore for keratitis-CXL (PACK-CXL) are performed while the patient is seated in an upright position at the slit lamp. METHODS: Topical anesthesia is applied in the waiting room, 10 minutes before the procedure. Once in the office or procedure room, eyelids and periorbital areas are disinfected with chloramphenicol and the patient is seated at the slit lamp. Epithelial debridement is performed with a cotton swab soaked in freshly prepared 40% ethanol, using 70 seconds of tapping, followed by gentle pressure to remove the epithelium. The patient is placed in the supine position for riboflavin application for 10 minutes. Stromal thickness is assessed using ultrasound pachymetry after 5 and 10 minutes. Finally, the patient is returned to the slit lamp to receive ultraviolet irradiation. RESULTS: CXL at the slit lamp is an easy-to-perform technique that substantially reduces the infrastructure needed to perform CXL and PACK-CXL procedures. CONCLUSIONS: A significant advantage of allowing CXL treatment at the slit lamp is that CXL technology can now be used in clinics that do not have easy access to an operating room infrastructure. Slit-lamp CXL can also reduce procedure costs by eliminating the technical fees related to the use of an operating room, making this treatment not only more accessible for patients, but also affordable. [J Refract Surg. 2021;37(2):78-82.].

Pupil influence on the quality of vision in rotationally asymmetric multifocal IOLs with surface-embedded near segment.

PURPOSE: To evaluate the influences of preoperative pupil parameters on the visual outcomes of the SBL-3, a rotationally asymmetric multifocal intraocular lens (IOL) with a surface-embedded near segment. SETTING: Cathedral Eye Clinic, Belfast, Northern Ireland, United Kingdom. DESIGN: Retrospective comparative case series. METHODS: Postoperatively, patients divided into 4 groups according to their pupil size as follows: Group A: 2.50 to 2.99 mm, Group B: 3.00 to 3.50 mm, Group C: 3.51 to 4.00 mm, and Group D: 4.01 to 4.50 mm. The uncorrected distance (UDVA), intermediate (UIVA), and near (UNVA) visual acuities, IOL centration and tilt, and quality of vision (QoV) questionnaires were compared between the 4 groups for 18 months postoperatively. RESULTS: The study comprised 90 patients (180 eyes). The mean preoperative pupil (photopic and mesopic) diameter was 4.3 mm ± 0.3 (SD) and 5.6 ± 1.4 mm, respectively, which decreased to 3.8 ± 0.7 mm and 4.9 ± 1.2 mm, respectively, at 18 months. Eighteen months postoperatively, both photopic and mesopic pupil groups had a statistically significant reduction in size from preoperative levels. No significant differences in UDVA, UIVA, and UNVA were found between the groups (P > .001). Significant differences in the QoV questionnaire day scores and night scores were found between the 4 groups (P < .001). CONCLUSIONS: The rotationally asymmetric multifocal IOL provided excellent optical performance during 18-months follow-up. The preoperative photopic pupil is an important parameter for consideration of this type of IOL because smaller pupils have a significant negative subjective impact on QoV.

Visual quality and performance comparison between 2 refractive rotationally asymmetric multifocal intraocular lenses.

PURPOSE: To compare the 12-month postoperative quality of vision and visual performance of 2 different refractive rotationally asymmetric multifocal intraocular lenses (IOLs). SETTING: Cathedral Eye Clinic, Belfast, Northern Ireland, United Kingdom. DESIGN: Retrospective case series. METHODS: Refractive lens exchange (RLE) patients were divided into 2 groups. Group A comprised eyes receiving a Lentis Mplus LS-312 MF30 IOL and Group B, eyes receiving a Lenstec SBL-3 IOL. Refraction, uncorrected (UDVA) and corrected distance visual acuities, uncorrected intermediate (UIVA) and near (UNVA) visual acuities, distance-corrected intermediate and near (DCNVA) visual acuities, and quality of vision were evaluated preoperatively and up to 12 months postoperatively. RESULTS: Each group comprised 90 eyes. Both groups had a high level of quality of vision 12 months postoperatively with no significant difference between the 2 groups (P = .919). There was no significant between-group difference in mean monocular and binocular UDVA, monocular UIVA, or monocular UNVA. Group B had statistically significantly better mean monocular DCNVA (P = .049), binocular UNVA (P = .011), and binocular DCNVA (P = .035). Group B had a higher percentage of complete spectacle independence. CONCLUSIONS: Both refractive rotationally asymmetric multifocal IOLs provided an excellent level of quality of vision 12 months postoperatively. Both IOL models restored distance, intermediate, and near visual function; however the IOLs in Group B provided better near visual performance.

Visual outcomes and patient satisfaction 3 and 12 months after implantation of a refractive rotationally asymmetric multifocal intraocular lens.

PURPOSE: To assess the 3-month and 12-month postoperative visual performance and subjective patient satisfaction after refractive lens exchange (RLE) with implantation of a rotationally asymmetric multifocal intraocular lens (IOL). SETTING: Cathedral Eye Clinic, Belfast, United Kingdom. DESIGN: Prospective case series. METHODS: The refraction, uncorrected (UDVA) and corrected distance visual acuities, uncorrected intermediate (UIVA) and near (UNVA) visual acuities, distance-corrected intermediate and near visual acuities, and a quality of vision (QoV) questionnaire were evaluated 3 months and 12 months after implantation of an SBL-3 IOL. RESULTS: The study enrolled 100 eyes of 50 patients. The mean monocular UDVA was -0.02 logarithm of minimum angle of resolution (logMAR) ± 0.12 (SD) 3 months postoperatively and -0.01 ± 0.10 logMAR at 12 months (P = .393). The mean monocular UIVA was 0.39 ± 0.11 logMAR and 0.41 ± 0.12 logMAR, respectively (P = .06). The mean monocular UNVA was 0.12 ± 0.13 logMAR and 0.14 ± 0.12 logMAR, respectively (P = .077). The mean QoV score was 8.26 ± 1.16 at 3 months with a significant improvement at 12 months, at which time the mean QoV score was 8.84 ± 1.08 (P ≤ .001). CONCLUSIONS: This asymmetric multifocal IOL provided excellent unaided vision with no significant difference in near, intermediate, and distance vision 3 months and 12 months postoperatively. However, there was a significant improvement in subjective outcomes at the second postoperative assessment, during which patients reported a significantly better QoV score and less blurred vision.

Repeated Cross-linking After a Short Time Does Not Provide Any Additional Biomechanical Stiffness in the Mouse Cornea In Vivo.

PURPOSE: To study whether repeated collagen cross-linking (CXL) performed in vivo in mice shows an additive effect on mechanical corneal stiffness. METHODS: In this experimental study, epithelium-off CXL was performed in a total of 18 eyes from male C57BL/6 mice, with 0.27%-riboflavin solution applied for 20 minutes, followed by ultraviolet-A (UVA) irradiation (365 nm, 9mW/cm2) for 2:50 minutes (fluence 1.53 J/cm2). CXL was performed as either a single (1×CXL) or a repeated (2×CXL) treatment. Un-irradiated corneas served as controls. In the 2×CXL group, the procedure was performed on day 1 and day 4 to ensure complete reepithelialization between sessions. Biomechanical analysis was performed on day 7. Corneas were harvested with a small scleral ring and mounted on a customized two-dimensional flap holder. The biomechanical measurement consisted of three parts: (1) pre-conditioned during three cycles from 0.04 to 0.4 N, (2) stress relaxation during 120 seconds following 0.4 N force application, and (3) stress-strain curve until break. RESULTS: After the relaxation period of 120 seconds, highly significant differences (P < .001) were found between the controls and both 1×CXL corneas and 2×CXL corneas. No significant difference (P = .70) was detected between the 1×CXL and 2×CXL groups. The stress remaining after relaxation was 355 ± 25.2 kPa in the control group, 457 ± 34.1 kPa in the 1×CXL group, and 463 ± 22.2 kPa in the 2×CXL group. No significant differences in the stress-strain curves were found between the conditions. CONCLUSIONS: Repeated CXL 3 days after the first procedure does not further increase corneal stiffness in mice in vivo. [J Refract Surg. 2017;33(1):56-60.].

Comparison of the visual performance and quality of vision with combined symmetrical inferonasal near addition versus inferonasal and superotemporal placement of rotationally asymmetric refractive multifocal intraocular lenses.

PURPOSE: To compare the postoperative quality of vision between different bilateral placements of near segments of rotationally asymmetric refractive multifocal intraocular lenses (IOLs) and to determine how this affects visual performance. SETTING: Cathedral Eye Clinic, Belfast, Northern Ireland, United Kingdom. DESIGN: Retrospective comparative case series. METHODS: The study enrolled consecutive patients having refractive lens exchange and implantation of rotationally asymmetric multifocal IOLs. Group 1 received bilateral SBL-3 IOLs and Group 2 received bilateral Lentis Mplus LS-312 MF30 IOLs, with the near segments placed inferonasally in each group. Group 3 received a Lentis Mplus LS-312 MF20 IOL in the dominant eye with the near segment positioned superotemporal and a Lenstec SBL-3 IOL positioned inferonasally in the fellow eye. Binocular uncorrected (UDVA) and corrected distance visual acuities, binocular uncorrected near (UNVA) and intermediate (UIVA) visual acuities, binocular distance-corrected near and intermediate visual acuities, and quality of vision were evaluated over 3 months postoperatively. RESULTS: The study enrolled 180 patients (360 eyes). There was no significant difference between the groups in binocular UDVA, UIVA, and UNVA; however, there was a significant difference between the groups in quality of vision (P ≤ .001). Group 3 had significantly better overall quality of vision. CONCLUSION: When implanting rotationally asymmetric multifocal IOLs, a combination of superotemporal placement of the near segment (+2.00 diopter [D] addition [add]) in the dominant eye with inferonasal placement of the near segment (+3.00 D add) in the fellow eye yielded consistent, high overall quality of vision and uncorrected visual acuity. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Threshold limit of postoperative astigmatism for patient satisfaction after refractive lens exchange and multifocal intraocular lens implantation.

PURPOSE: To determine the degree of tolerance toward different magnitudes of residual refractive astigmatism and corneal astigmatism and the angles of corneal astigmatism after implantation of an asymmetric multifocal intraocular lens (IOL). SETTING: Cathedral Eye Clinic, Belfast, United Kingdom. DESIGN: Retrospective comparative case series. METHODS: The study enrolled patients having refractive lens exchange and implantation of a Lentis Mplus LS-312 MF30 IOL. Uncorrected (UDVA) and corrected distance visual acuities, uncorrected near and intermediate visual acuities, and quality-of-vision questionnaires were evaluated. Groups were categorized based on the magnitude of refractive astigmatism and corneal residual astigmatism. Refractive astigmatism of less than 0.50 diopter (D) and more than 0.50 D and corneal astigmatism of 0.50 D or less, 0.51 to 0.75 D, 0.76 to 1.00 D, and more than 1.00 D were categorized. RESULTS: The study comprised 117 patients (234 eyes). There was a significant difference in UDVA (P = .003), refractive sphere (P = .001), and defocus equivalent (P ≤ .001) between the residual refractive astigmatism groups; however, there was no difference in quality of vision (P = .28). The same was found for corneal astigmatism with UDVA (P ≤ .001) and quality of vision (P = .16). The angle of corneal astigmatism in relation to IOL placement did not statistically affect postoperative outcomes. CONCLUSIONS: The IOL appeared to subjectively tolerate residual astigmatism well despite a statistically significant difference in UDVA with higher magnitudes of residual astigmatism. The angle of residual corneal astigmatism in relation to IOL placement did not have a significant effect on postoperative outcomes. FINANCIAL DISCLOSURE: None of the authors has a financial or proprietary interest in any material or method mentioned.

Optimized Visual Outcome After Asymmetrical Multifocal IOL Rotation.

PURPOSE: To report improved visual outcome after rotation of an asymmetrical multifocal intraocular lens (IOL). METHODS: Case report. RESULTS: A 58-year-old patient underwent bilateral phacoemulsification with asymmetrical multifocal IOL implantation. Postoperative uncorrected distance visual acuity (UDVA) was 0.0 logMAR (20/20 Snellen) and uncorrected near visual acuity was 0.0 logMAR (20/20 Snellen) in both eyes. Quality of vision questionnaire scores for day and night were 5 and 7, respectively. The center of the multifocal IOL in the dominant eye was initially found to be 0.2 mm superotemporally displaced, increasing the percentage area of 'near-add' compared to 'distance-add' within the physiological pupil. Rotation of this IOL 120° clockwise greatly improved the IOL centration within the pupil center and resulted in an immediate improvement in UDVA to -0.1 logMAR (20/16 Snellen) and quality of vision questionnaire scores to 8 and 9, respectively. CONCLUSIONS: Assessment of the centration of an asymmetrical multifocal IOL is important, particularly if there are dysphotoptic or other visual complaints. [J Refract Surg. 2016;32(7):494-496.].

Analysis of Riboflavin Compounds in the Rabbit Cornea In Vivo.

PURPOSE: To investigate the composition and concentration of individual riboflavin compounds in the corneal stroma in vivo after soaking with various commercially available riboflavin formulations. METHODS: Experiments were performed in 26 rabbit corneas in vivo: 24 corneas were soaked with riboflavin formulations for 30 minutes or with 0.9% NaCl for control (n = 2). After treatment, corneas were excised and prepared for ultra-high-pressure liquid chromatography (UHPLC) analysis. Additionally, computational chemical analysis of riboflavin compounds and keratan sulfate were performed. RESULTS: The amount of riboflavin and riboflavin phosphate isomers in cornea decreased by a factor of 10 to 100, when compared to the amount in riboflavin formulations. In particular, we found an inverse relationship in the ratio of riboflavin to riboflavin phosphate isomer concentration between formulations and cornea. The electronegativity and ionization potential of riboflavin and phosphate isomers are different. CONCLUSIONS: The inverse relationship observed might be explained by a stronger electronegativity of the phosphate isomers, leading to a stronger repulsion by corneal proteoglycans. Indicating the individual concentration of riboflavin compounds in formulations is more representative than the total riboflavin concentration. Riboflavin formulations and CXL protocols might be improved considering the differences in diffusion and ionization potentials of the different riboflavin compounds.

Increased Biomechanical Efficacy of Corneal Cross-linking in Thin Corneas Due to Higher Oxygen Availability.

PURPOSE: To compare the currently available ultraviolet-A (UV-A) corneal cross-linking (CXL) treatment protocols for thin corneas with respect to oxygen, UV fluence, and osmotic pressure. METHODS: Freshly enucleated murine (n = 16) and porcine (n = 16) eyes were used. The dependency on oxygen and the amount of UV absorption were evaluated using different CXL protocols, including standard CXL, contact lens-assisted CXL (caCXL), and CXL after corneal swelling. The CXL protocol was adapted from the treatment parameters of the human cornea to fit the thickness of murine and porcine corneas. Immediately after CXL, the corneas were subjected to biomechanical testing, including preconditioning, stress relaxation at 0.6 MPa, and stress-strain extensiometry. A two-element Prony series was fitted to the relaxation curves for viscoelastic characterization. RESULTS: Standard CXL was most efficient; prior corneal swelling reduced the long-term modulus by 6% and caCXL by 15% to 20%. Oxygen reduction decreased the long-term modulus G∞ by 14% to 15% and the instantaneous modulus G0 by 2% to 5%, and increased the short-term modulus G2 by 22% to 31%. Reducing the amount of absorbed UV energy decreased the long-term modulus G∞ by 5% to 34%, the instantaneous modulus G0 by 7% to 29%, and the short-term modulus G2 by 17% to 20%. The amount of absorbed UV light was more important in porcine than in murine corneas. CONCLUSIONS: The higher oxygen availability in thin corneas potentially increases the overall efficacy of riboflavin UV-A CXL compared to corneas of standard thickness. Clinical protocols for thin corneas should be revised to implement these findings.

Establishing Corneal Cross-Linking With Riboflavin and UV-A in the Mouse Cornea In Vivo: Biomechanical Analysis.

PURPOSE: To establish corneal cross-linking (CXL) with riboflavin and UV-A in in the mouse cornea in vivo and to develop tools to measure the biomechanical changes observed. METHODS: A total of 55 male C57BL/6 wild-type mice (aged 5 weeks) were divided into 14 groups. Standard CXL parameters were adapted to the anatomy of the mouse cornea, and riboflavin concentration (0.1%-0.5%) and fluence series (0.09-5.4 J/cm²) were performed on the assumption of the endothelial damage thresholds. Untreated and riboflavin only corneas were used as controls. Animals were killed at 30 minutes and at 1 month after CXL. Corneas were harvested. Two-dimensional (2D) biomechanical testing was performed using a customized corneal holder in a commercially available stress-strain extensometer/indenter. Both elastic and viscoelastic analyses were performed. Statistical inference was performed using t-tests and specific mathematical models fitted to the experimental stress-strain and stress-relaxation data. Adjusted P values by the method of Benjamini and Hochberg are reported. RESULTS: For all CXL treatment groups, stress-relaxation showed significant differences (P < 0.0001) after 120 seconds of constant strain application, with cross-linked corneas maintaining a higher stress (441 ± 40 kPa) when compared with controls (337 ± 39 kPa). Stress-strain analysis confirmed these findings but was less sensitive to CXL-induced changes: at 0.5% of strain, cross-linked corneas remained at higher stress (778 ± 111 kPa) when compared with controls (659 ± 121 kPa). CONCLUSIONS: Cross-linking was induced in the mouse cornea in vivo, and its biomechanical effect successfully measured. This could create opportunities to study molecular pathways of CXL in transgenic mice.

PACK-CXL: Corneal Cross-linking for Treatment of Infectious Keratitis.

This article discusses corneal cross-linking (CXL) and how it transitioned from a modality for treating corneal ectatic disorders to an inventive means of treating infectious keratitis. Initially, CXL was successfully developed to halt the progression of ectatic diseases such as keratoconus, using the standard Dresden protocol. Later, indications were extended to treat iatrogenic ectasia developing after laser-assisted in situ keratomileusis (LASIK) and photo-refractive keratectomy (PRK). At the time, it had been postulated that the combination of ultraviolet light with riboflavin could not only biomechanically strengthen the cornea but also was capable of destroying living cells and organisms including keratocytes and pathogens. Thus a new and innovative concept of treatment for infectious keratitis emerged through the use of CXL technology. Initially only advanced infectious melting ulcers resisting standard microbicidal therapy were treated with CXL in addition to standard therapy. In subsequent studies CXL was also used to treat bacterial keratitis as first line therapy without the use of concomitant antibiotic therapy. With the increasing interest in CXL technology to treat infectious keratitis and to clearly separate its use from the treatment of ectatic disorders, a new term was adopted at the 9(th) CXL congress in Dublin for this specific indication: PACK-CXL (photoactivated chromophore for infectious keratitis). PACK-CXL has the potential to eventually become an interesting alternative to standard antibiotic therapy in treating infectious corneal disorders, and may help reduce the global burden of microbial resistance to antibiotics and other therapeutic agents.

Failure analysis of adhesive restorations with SEM and OCT: from marginal gaps to restoration loss.

OBJECTIVE: The objective of this study was to analyse the failure mode of adhesive interfaces by comparing OCT and scanning electron microscope (SEM) analysis of class V restoration margins located on enamel and dentin. MATERIALS AND METHODS: Three groups were tested that differed in the application of a 3-step etch-and-rinse adhesive system (OptiBond FL) prior to cavity filling with restorative composite resin (Clearfil AP-X). After tooth restoration and polishing, the samples were loaded in a fatigue machine, and adhesive interfaces were evaluated with OCT and SEM. RESULTS: Important and complementary information could be obtained with OCT analysis in respect to how marginal defects can propagate inside the cavity, compromising the restoration's long-term performance. A self-etching effect was observed with OptiBond FL due to the presence of an acidic primer (GPDM) within its composition. Our results could show that areas of bonding and gaps coexisted within the same restoration. CONCLUSIONS: When marginal imperfections, or non-continuous margins, were detected by SEM, also imperfections beneath the surface could be observed at the tooth-restoration interface with OCT. Restoration loss occurred above the borderline of 50% of marginal gaps on enamel and dentin. CLINICAL RELEVANCE: Marginal discrepancies of adhesive restorations can propagate inside the cavity and lead to restoration loss.

Antibacterial efficacy of accelerated photoactivated chromophore for keratitis-corneal collagen cross-linking (PACK-CXL).

PURPOSE: To investigate whether optimized photoactivated chromophore for keratitis-corneal collagen cross-linking (PACK-CXL) treatment settings allow accelerating treatment while maintaining antibacterial efficacy. METHODS: Staphylococcus aureus and Pseudomonas aeruginosa strains were irradiated with ultraviolet-A light of equal fluence but different intensity settings (18 mW/cm² for 5 minutes and 36 mW/cm² for 2.5 minutes). The killing rate was determined by comparing the number of colony-forming units between cross-linked specimens and non-irradiated controls. The potential additional effect of 0.001% benzalkonium chloride was also investigated. RESULTS: The killing rates for Staphylococcus aureus were 92.5% ± 5.5% (5 minutes at 18 mW/cm²) and 94.4% ± 2.9% (2.5 minutes at 36 mW/cm²). For Pseudomonas aeruginosa, the killing rates were 93.2% ± 8.3% (5 minutes at 18 mW/cm²) and 92.9% ± 5.0% (2.5 minutes at 36 mW/cm²). The presence of benzalkonium chloride in the riboflavin solution did not increase the killing rate significantly. CONCLUSIONS: The antibacterial efficacy of PACK-CXL follows the Bunsen-Roscoe law of reciprocity and can be maintained even when the irradiation intensity is considerably increased. These optimized settings may allow a shortened treatment time in the future for PACK-CXL and thus help facilitate the transition from the operating room to the slit lamp for treatment.

Accelerated photoactivated chromophore for keratitis-corneal collagen cross-linking as a first-line and sole treatment in early fungal keratitis.

PURPOSE: To report the use of accelerated photoactivated chromophore for keratitis-corneal collagen cross-linking (PACK-CXL) as a first-line treatment in a patient with an atypical fungal keratitis. METHODS: Case report and literature review. RESULTS: A patient who presented with a painful peripheral corneal infiltrate underwent PACK-CXL with a local limited abrasion and accelerated ultraviolet-A irradiation at 365 µm and 9 mW/cm² for 10 minutes. Cultures grew Aureobasidium pullulans. The corneal epithelium closed completely within 3 days and the infiltrate was completely eradicated without administration of antibiotics. CONCLUSIONS: Accelerated PACK-CXL was successfully used as a first-line and sole treatment in a case of early fungal keratitis caused by Aureobasidium pullulans. Further characterization of the antifungal effect of PACK-CXL is needed in prospective studies.

Additive effect of repeated corneal collagen cross-linking in keratoconus.

PURPOSE: To report the long-term clinical outcome in a patient diagnosed as having bilateral progressive keratoconus who received a single corneal collagen cross-linking (CXL) treatment in the right eye and repeated CXL in the left eye. METHODS: Observational case report. Topographical changes were assessed by high-resolution Scheimpflug imaging. The right eye underwent a standard epithelium-off CXL procedure in February 2008, followed by the left eye 4 weeks later. In 2012, the left eye was treated with CXL for a second time. Irradiation was performed in all cases at a fluence of 5.4 J/cm². Energy settings were 30 minutes @ 3 mW/cm² for the CXL procedures performed in 2008, and 10 minutes @ 9 mW/cm² for the second CXL procedure of the left eye that was performed in 2012. RESULTS: The right eye that underwent a single CXL procedure showed a flattening of keratometry values between 2008 and 2012, followed by stabilization. The left eye showed a similar flattening effect between 2008 and 2012, followed by another flattening effect after the second CXL procedure and accompanied by a distinct increase in corrected distance visual acuity. CONCLUSIONS: Following repeated CXL, the corneal stroma and endothelium remained inconspicuous, and postoperative haze and visibility of the stromal demarcation line was similar to what is usually observed after a single CXL procedure. Whether the additive flattening effect of the anterior surface observed in this single case goes along with an additive increase in biomechanical stiffness remains to be seen.

Determination of the excimer laser ablation rate in previously cross-linked corneas.

PURPOSE: To evaluate the need for and quantify the extent of nomogram adjustments to compensate for potential changes in the amount of effective corneal stroma ablated in previously cross-linked corneas. METHODS: Ex vivo porcine corneas were divided into two groups (the corneal cross-linking [CXL] group, n = 30; and the control group, n = 3): these experimental corneas underwent CXL including deepithelialization, instillation of riboflavin solution for 25 minutes, and ultraviolet-A irradiation at 9 mW/cm2 for 10 minutes. The control group was deepithelialized only. Four consecutive excimer laser ablations of 50 pm each were performed (AMARIS 750S; SCHWIND eye-tech-solutions, Kleinostheim Germany), and stromal bed thickness was measured with a built-in optical coherence pachymeter. To determine the potential influence of riboflavin, a third group (the riboflavin group, n = 12) underwent deepithelialization and instillation of riboflavin, but no ultraviolet-A irradiation. RESULTS: The mean individual ablation depth across the four ablations was significantly smaller in cross-linked corneas (-17%) when compared to untreated control corneas (P < .001). A consistent reduction of 12% was observed via a cumulative analysis when assessing the relative isolated effect of CXL on the ablation rate. There was no significant effect from riboflavin in the deeper ablations, except for the first ablation (68.6 + 1.1 mm [range: 1 to 50 pm]). This may be due to a measurement error in pachymetric readings due to the thin film of riboflavin on the surface that resists even extensive rinsing. CONCLUSIONS: CXL reduces the corneal ablation depth of excimer lasers in the anterior 200 pm of the porcine cornea by approximately 12%. Further clinical studies are needed to validate these findings in human corneas.