Faculty Bibliography

PURPOSE/OBJECTIVE:To study the mid-term effects of implanting a single intracorneal ring segment (ICRS) for treatment of mild to moderate progressive keratoconus. METHODS:This retrospective study was conducted on patients with progressive keratoconus treated with ICRS. The mean follow-up time was 15.2 ± 8.8 (range, 7-26) months before and 27.8 ± 7.5 (range, 18-35) months after surgery. Patients received no other treatment during this time. Of the cases studied, 59.1% had inferior keratoconus. RESULTS:Thirty eyes of 30 patients with a mean age of 27.5 ± 4.6 years were included in the study. Corrected distance visual acuity decreased by 1 line during the preoperative follow-up and improved by 2 lines after surgery (P < 0.05). Maximum keratometry (Kmax) of the anterior (2.39 ± 0.75 D) and posterior (0.33 ± 0.32 D) corneas at 3 mm and anterior Kmax at 8 mm (2.39 ± 0.95 D) decreased after treatment (all P < 0.05). The posterior Q value shifted toward a more oblate curvature (0.50 ± 0.52, P = 0.023). Decreases in anterior elevation at the thinnest point (5.22 ± 7.21 μm) and posterior corneal central elevation (8.89 ± 11.26 μm) were significant (both P < 0.05). Corneal thickness at the center (11.11 ± 12.38 μm) and thinnest point (15.89 ± 12.75 μm) increased after treatment (all P < 0.001). Other significant changes included postoperative decreases in the keratoconus index (0.12 ± 0.06), index of height decentration (0.06 ± 0.05), index of surface variance (27.32 ± 13.08), index of vertical asymmetry (0.42 ± 0.21), index of height asymmetry (8.42 ± 20.57), and an increase in the center keratoconus index (0.01 ± 0.02) (P < 0.001). CONCLUSIONS:This study demonstrates that ICRS implantation provides favorable mid-term outcomes in treatment of mild and moderate progressive keratoconus and can improve corneal indices compared with their preoperative states.

PURPOSE/OBJECTIVE:To determine the corneal weakening induced by different re-treatment options after small incision lenticule extraction (SMILE) and investigate the potential of corneal cross-linking (CXL) to reestablish the original corneal stress resistance. METHODS:, 10 min) was performed in two groups with currently common enhancement techniques: following cap-to-flap conversion (-3D LASIK enhancement) and in controls. Biomechanical properties were measured with stress-strain extensometry ranging from 1.27 to 12.5 N. RESULTS:The Re-SMILE and PRK enhancement did not significantly reduce the overall elastic modulus of the cornea compared to controls (24.7 ± 2.23 and 22.7 ± 2.61 versus 23.8 ± 3.35 MPa, P ≥ .176), whereas LASIK enhancement did (22.2 ± 3.37 MPa, P = .048). CXL treatment significantly increased the elastic modulus compared to all non-cross-linked conditions (P ≤.001). Refractive surgery decreased the overall elastic modulus by 7%, whereas CXL increased it by 20%. CONCLUSIONS:In enhancement, the corneal biomechanical integrity is less affected with both Re-SMILE and PRK enhancement. Corneal weakening through laser refractive surgery is small compared to the stiffening effect after CXL. [J Refract Surg. 2017;33(3):193-198.].

PURPOSE/OBJECTIVE:To develop an algorithm to predict the stiffening effect of CXL and to verify the accuracy with results obtained from experimental measurements. METHODS:and irradiation times from 8 to 30 minutes. Stress-relaxation measurements were performed in fresh-enucleated porcine (n = 66) and rabbit (n = 2) eyes directly after treatment, using a load of 0.6 MPa. RESULTS:= 0.9961). CONCLUSIONS:The proposed model, supported by data in porcine, murine, and lapine corneas, suggests a possibility of also predicting the biomechanical CXL efficacy in human corneas. The biomechanical efficacy of CXL may be increased by prolonged UV irradiation at reduced irradiances or by a higher oxygen pressure in the environment. Pulsed CXL does not accelerate CXL or increase its efficacy when compared to standard CXL of the same irradiation duration. This model might be used to calculate customized irradiation settings for high-risk cases, but also topography-guided CXL treatments. [J Refract Surg. 2017;33(2):128-136.].

PURPOSE/OBJECTIVE:To study whether repeated collagen cross-linking (CXL) performed in vivo in mice shows an additive effect on mechanical corneal stiffness. METHODS:). 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.].

PURPOSE/OBJECTIVE:To morphologically, biochemically, and physiologically characterize corneal cross-linking with riboflavin and UV-A light (CXL) in a newly established in vivo murine model. METHODS:= 67) were treated with various CXL protocols, with modification of the following parameters: total energy (fluence) used, duration of UV-A irradiation, continuous versus pulsed irradiation, and CXL under hypoxic conditions (contact lens). Corneas were evaluated biomicroscopically, histologically, and using optical coherence tomography. Conformational collagen changes were evaluated via changes in the speed of enzymatic digestion. RESULTS:reduced epithelial thickness, but maintained a transparent cornea after 1 month. Pulsed UV irradiation inhibited neovascularization, but favored scar formation. Changes in the speed of enzymatic digestion suggest that CXL in mice, when compared to humans, requires less UV-A energy than the difference in corneal thickness between the species would suggest. CONCLUSIONS:We demonstrated the in vivo response of very strong and very weak CXL and identified the best suited range of UV fluence in murine corneas. The presented murine CXL model may be helpful in future research addressing cellular and molecular pathways associated to CXL treatment. TRANSLATIONAL RELEVANCE/CONCLUSIONS:Adverse tissue reactions following CXL treatment were observed, if the administered UV energy was out of the treatment window-raising concern about novel CXL treatment protocols that have not been previously validated in an experimental setting.