Olivier Richoz

Corneal biomechanical properties at different corneal cross-linking (CXL) irradiances.

PURPOSE New corneal cross-linking (CXL) devices are capable of using higher UV-A light irradiances than used in original CXL protocols. The Bunsen-Roscoe law states that a photochemical reaction should stay constant if the delivered total energy is kept constant; however, little clinical data are available to support this hypothesis. METHODS We investigated the biomechanical properties of four groups (n = 50 each) of porcine corneas. Three groups were exposed to riboflavin 0.1 % and UV-A irradiation of equal total energy (3 mW/cm(2) for 30 minutes, 9 mW/cm(2) for 10 minutes, and 18 mW/cm(2) for 5 minutes). Controls were exposed to riboflavin 0.1% without irradiation. Youngs modulus of 5-mm wide corneal strips was used as an indicator of corneal stiffness. RESULTS We observed a decreased stiffening effect with increasing UV-A intensity. Youngs modulus at 10% strain showed significant differences between 3 mW/cm(2) and 9 mW/cm(2) (P = 0.002), 3 mW/cm(2) and 18 mW/cm(2) (P = 0.0002), 3 mW/cm(2) and the control group (P < 0.0001), and 9 mW/cm(2) and the control group (P = 0.015). There was no difference between 18 mW/cm(2) and the control group (P = 0.064) and between 9 mW/cm(2) and 18 mW/cm(2) (P = 0.503). CONCLUSIONS The biomechanical effect of CXL decreased significantly when using high irradiance/short irradiation time settings. Intrastromal oxygen diffusion capacity and increased oxygen consumption associated with higher irradiances may be a limiting factor leading to reduced treatment efficiency. Our results regarding the efficiency of high-irradiance collagen cross-linking (CXL) raise concerns about the clinical efficiency of the new high-irradiance CXL devices already used in clinical practice without proper validation.

Corneal Collagen Cross-Linking for Ectasia after LASIK and Photorefractive Keratectomy: Long-Term Results

PURPOSE To report the long-term results of corneal collagen cross-linking (CXL) in ectasia after LASIK and photorefractive keratectomy (PRK). DESIGN Retrospective, interventional cases series. PARTICIPANTS Twenty-six eyes of 26 patients (18 male, 8 female) with postoperative ectasia after LASIK (23 eyes) and PRK (3 eyes) were included with a mean age of 35 ± 9 years at the time of treatment and a mean follow-up of 25 months (range, 12-62 months). METHODS All consecutive patients treated with CXL for progressive ectasia after LASIK or PRK at the Institute for Refractive and Ophthalmic Surgery, Zurich, Switzerland between 2004 and 2010 were included. MAIN OUTCOME MEASURES Corrected distance visual acuity (CDVA), maximum keratometry readings (K(max)), minimum radius of curvature (R(min)), and 6 corneal topography indices were assessed in this study. RESULTS Mean CDVA before CXL was 0.5 logarithm of the minimum angle of resolution (logMAR) units, which improved to a mean of 0.3 logMAR units (P<0.001). Corrected distance visual acuity improved 1 line or more in 19 cases and remained unchanged in 7 patients. Mean K(max) after CXL of 50.9 ± 4.9 diopters (D) was significantly lower (P<0.001) than mean pre-CXL K(max) of 52.8 ± 5 D. The R(min) after CXL was increased significantly (P = 0.006), whereas the index of surface variance (P = 0.03), the index of vertical asymmetry (P = 0.04), the keratoconus index (P = 0.03), and the central keratoconus index (P = 0.016) were reduced significantly. CONCLUSIONS Ectasia after LASIK and PRK was arrested by CXL with stabilization or improvement of CDVA and K(max) after a mean follow-up of 25 months. There were improvements in 4 topography indices, suggesting a more regular corneal surface.

Safety profile of high-fluence corneal collagen cross-linking for progressive keratoconus: preliminary results from a prospective cohort study.

PURPOSE To investigate the effect of high-fluence corneal collagen cross-linking (CXL) with riboflavin and ultraviolet-A in the management of progressive keratoconus. METHODS Preliminary results from a prospective cohort study. Seven eyes from 7 patients with progressive keratoconus subjected to CXL were included. CXL was performed as a standard epithelium-off procedure, irradiating with high-fluence settings (18 mW/cm(2) for 5 minutes). Endothelial cell density (ECD), speed of postoperative epithelial healing, maximal and average keratometric readings (Kmax and Kmean, respectively) of the anterior corneal surface, and corrected distance visual acuity (CDVA) were evaluated preoperatively and at 1 and 6 months after CXL. One-way analysis of variance was applied for statistical analysis. P values less than .05 were considered significant. RESULTS ECD did not change significantly postoperatively and complete epithelial healing occurred in all eyes within 96 hours postoperatively. No morphological alterations in the corneal limbus were observed. Kmax, Kmean, and CDVA showed no significant changes at 1 and 6 months postoperatively. No complications were observed postoperatively. CONCLUSIONS Although the preliminary results are not sufficient for a valid evaluation of the biomechanical effect and the overall safety profile of high-fluence CXL in vivo, they demonstrate that CXL at 18 mW/cm(2) for 5 minutes affects neither endothelial cell density nor the speed of epithelial healing, an indirect indicator of limbal stem cell function.

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.

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.

Collagen copolymer toric phakic intraocular lens for residual myopic astigmatism after intrastromal corneal ring segment implantation and corneal collagen crosslinking in a 3-stage procedure for keratoconus.

Purpose To evaluate staged combined treatment for keratoconus with intrastromal corneal ring segment (ICRS) implantation followed by corneal collagen crosslinking (CXL) with riboflavin–ultraviolet‐A (UVA) and then toric implantable collagen copolymer phakic intraocular lens (pIOL) implantation. Setting Large private ophthalmic hospital system. Design Case series. Methods Eyes with progressive keratoconus had ICRS implantation, then CXL, and then pIOL implantation (minimum 6 months between procedures). Results The study enrolled 14 eyes (9 patients). After the combined treatments, the mean decimal uncorrected distance visual acuity (UDVA) and mean decimal corrected distance visual acuity (CDVA) were significantly improved from 0.01 and 0.14, respectively, preoperatively to 0.44 and 0.57, respectively (P<.0001). The mean manifest refraction spherical equivalent decreased from −16.40 diopters (D) ± 3.56 (SD) (range −11.50 to −22.50 D) to −0.80 ± 1.02 D (range −2.00 to +2.00 D) after the combined treatments (P<.0001). The mean refractive astigmatism decreased from −4.73 ± 1.32 D (range −3.00 to −7.00 D) to −0.96 ± 0.35 D (range −0.50 to −1.50 D) (P<.0001). The mean steep and mean flat keratometry values reduced from 60.57 D and 56.16 D, respectively, to 54.48 D and 53.57 D (P<.0001), respectively. No intraoperative or postoperative complications occurred. Conclusions A combined 3‐stage‐approach keratoconus treatment comprising ICRS implantation followed by CXL and then toric pIOL implantation was effective in improving functional vision and reducing disease progression. Longer term studies are required for further evaluation and comparison with other methods. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

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 9th 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.

Impact of Fluorescein on the Antimicrobial Efficacy of Photoactivated Riboflavin in Corneal Collagen Cross-linking

PURPOSE To investigate the effect of fluorescein on the antimicrobial efficacy of photoactivated riboflavin in corneal collagen cross-linking (CXL) in vitro. METHODS The ultraviolet light-A (UVA) absorption by fluorescein and riboflavin in different concentrations was analyzed with a spectrophotometer. The killing rate of Staphylococcus aureus strains after CXL with UV-A irradiation using different solutions containing riboflavin and/or fluorescein, was evaluated in vitro. RESULTS Fluorescein absorbed UV-A to a significant extent, which augmented with increasing concentration. Moreover, addition of fluorescein to the riboflavin solution contributed to a significant reduction of the killing rate of S. aureus strains after 30 minutes of UV-A irradiation in vitro with a killing rate of 85%, whereas it was 47% in the presence of 2% fluorescein (P = .0247). CONCLUSIONS The results indicate that fluorescein competes with riboflavin for the absorption of UV-A during CXL and reduces the antimicrobial effect of the procedure. The authors recommend that physicians treating infectious ulcerative keratitis by CXL should not stain the cornea with fluorescein for visualization of the corneal ulceration prior to CXL

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.

The Effect of Standard and High-Fluence Corneal Cross-Linking (CXL) on Cornea and Limbus

PURPOSE When treating peripheral ectatic disease-like pellucid marginal degeneration (PMD), corneal cross-linking with UV-A and riboflavin (CXL) must be applied eccentrically to the periphery of the lower cornea, partly irradiating the corneal limbus. Here, we investigated the effect of standard and double-standard fluence corneal cross-linking with riboflavin and UV-A (CXL) on cornea and corneal limbus in the rabbit eye in vivo. METHODS Epithelium-off CXL was performed in male New Zealand White rabbits with two irradiation diameters (7 mm central cornea, 13 mm cornea and limbus), using standard fluence (5.4 J/cm(2)) and double-standard fluence (10.8 J/cm(2)) settings. Controls were subjected to epithelial removal and riboflavin instillation, but were not irradiated with UV-A. Following CXL, animals were examined daily until complete closure of the epithelium, and at 7, 14, 21, and 28 days. Animals were killed and a corneoscleral button was excised and processed for light microscopy and immunohistochemistry. RESULTS For both irradiation diameters and fluences tested, no signs of endothelial damage or limbal vessel thrombosis were observed, and time to re-epithelialization was similar to untreated controls. Histological and immunohistochemical analysis revealed no differences in the p63 putative stem cell marker expression pattern. CONCLUSIONS Even when using fluence twice as high as the one used in current clinical CXL settings, circumferential UV-A irradiation of the corneal limbus does not alter the regenerative capacity of the limbal epithelial cells, and the expression pattern of the putative stem cell marker p63 remains unchanged. This suggests that eccentric CXL may be performed safely in PMD.