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.

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.

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.

Impact of hypothermia on the biomechanical effect of epithelium-off corneal cross-linking.

BACKGROUND: The corneal cross-linking (CXL) photochemical reaction is essentially dependent on oxygen and hypothermia, which usually leads to higher dissolved oxygen levels in tissues, with potentially greater oxygen availability for treatment. Here, we evaluate whether a reduction of corneal temperature during CXL may increase oxygen availability and therefore enhance the CXL biomechanical stiffening effect in ex vivo porcine corneas. METHODS: One hundred and twelve porcine corneas had their epithelium manually debrided before being soaked with 0.1% hypo-osmolaric riboflavin. These corneas were equally assigned to one of four groups. Groups 2 and 4 underwent accelerated epithelium-off CXL using 9 mW/cm2 irradiance for 10 min, performed either in a cold room temperature (group 2, 4 °C) or at standard room temperature (group 4, 24 °C). Groups 1 and 3 served as non-cross-linked, temperature-matched controls. Using a stress-strain extensometer, the elastic moduli of 5-mm wide corneal strips were analyzed as an indicator of corneal stiffness. RESULTS: Accelerated epithelium-off CXL led to significant increases in the elastic modulus between 1 and 5% of strain when compared to non-cross-linked controls (P < 0.05), both at 4 °C (1.40 ± 0.22 vs 1.23 ± 0.18 N/mm) and 24 °C (1.42 ± 0.15 vs 1.19 ± 0.11 N/mm). However, no significant difference was found between control groups (P = 0.846) or between groups in which CXL was performed at low or standard room temperature (P = 0.969). CONCLUSIONS: Although initial oxygen availability should be increased under hypothermic conditions, it does not appear to play a significant role in the biomechanical strengthening effect of epithelium-off CXL accelerated protocols in ex vivo porcine corneas.

Individualized Corneal Cross-linking With Riboflavin and UV-A in Ultrathin Corneas: The Sub400 Protocol.

PURPOSE: To determine whether corneal cross-linking (CXL) with individualized fluence ("sub400 protocol") is able to stop keratoconus (KC) progression in ultrathin corneas with 12-month follow-up. DESIGN: Retrospective, interventional case series. METHODS: Thirty-nine eyes with progressive KC and corneal stromal thicknesses from 214 to 398 µm at the time of ultraviolet irradiation were enrolled. After epithelium removal, ultraviolet irradiation was performed at 3 mW/cm2 with irradiation times individually adapted to stromal thickness. Pre- and postoperative examinations included corrected distance visual acuity (CDVA), refraction, Scheimpflug, and anterior segment optical coherence tomography imaging up to 12 months after CXL. Outcome measures were arrest of KC progression at 12 months postoperatively and stromal demarcation line (DL) depth. RESULTS: Thirty-five eyes (90%) showed tomographical stability at 12 months after surgery. No eyes showed signs of endothelial decompensation. A significant correlation was found between DL depth and irradiation time (r = +0.448, P = .004) but not between DL depth and change in Kmax (r = -0.215, P = .189). On average, there was a significant change (P < .05) in thinnest stromal thickness (-14.5 ± 21.7 µm), Kmax (-2.06 ± 3.66 D) and densitometry (+2.00 ± 2.07 GSU). No significant changes were found in CDVA (P = .611), sphere (P = .077), or cylinder (P = .915). CONCLUSIONS: The "sub400" individualized fluence CXL protocol standardizes the treatment in ultrathin corneas and halted KC progression with a success rate of 90% at 12 months. The sub400 protocol allows for the treatment of corneas as thin as 214 µm of corneal stroma, markedly extending the treatment range. The DL depth did not predict treatment outcome. Hence, the depth is unlikely related to the extent of CXL-induced corneal stiffening but rather to the extent of CXL-induced microstructural changes and wound healing.

Diffuse and patchy intra-myocardial fat deposition in left ventricle: unclassified cardiomyopathy in an obese woman without pathological condition.

Fat deposition in the left ventricle in patients without proven myocardial diseases has not been sufficiently investigated. In this paper, a case of diffuse and patchy intramyocardial fat deposition in the left ventricular myocardium in a patient with no cardiac disease history has been detected by cardiac magnetic resonance imaging (CMRI). Such a finding would not be considered a usual cardiomyopathy and further studies are needed to investigate its prevalence, pathophysiological mechanisms, and prognosis.