The meaning of the demarcation line after riboflavin-UVA corneal collagen crosslinking

Introduction: The demarcation line (DL) observed since the pioneering crosslink (CLX) protocol at the posterior edge of the cross-linked stroma has been universally accepted as a therapeutic milestone of treatment. Numerous laboratory and clinical CXL studies demonstrate that a deeper DL is associated with a higher amount and saturation level of crosslinks, a more pronounced stiffening effect, and a more durable ectasia stability. Areas covered: A critical revision of laboratory, clinical, and analytical studies on the DL depth supports the significance of the DL as an evaluator of the performance of CLX procedures in terms of biomechanical efficacy and safety avoiding extensive experiments. A mechanical approach based on experimental data shows that the DL depth obtained with different CXL protocols relates with an asymptotic non-linear increasing function to the modified biomechanical corneal stiffness (elastic modulus). Expert opinion: The strong connection between the depth of the DL and the increase of the biomechanical efficacy can be explained by means of UV cross-linking chemical investigations demonstrating that only a limited amount of free reactive collagen residues is involved in the short-wave UV-mediated CXL. Thus, the CXL density can rise only up to an upper boundary value, i.e. the saturation value

Corneal melting after collagen cross-linking for keratoconus: a case report

<p>Abstract</p> <p>Introduction</p> <p>Corneal collagen cross-linking is a rather new technique that uses riboflavin and ultraviolet A light for collagen fiber stabilization in keratoconus corneas. Other than reversible side effects, the preliminary results of corneal collagen cross-linking studies suggest that it is a rather safe technique. In this report, we demonstrate a case of corneal melting after corneal collagen cross-linking for keratoconus corneas associated with an acute inflammatory response.</p> <p>Case presentation</p> <p>A 23-year-old Caucasian man with keratoconus cornea stage 1 to 2 underwent uneventful corneal collagen cross-linking treatment according to the Dresden protocol. The next day the patient had intense photophobia, watering and redness of the eye, and his visual acuity was limited to counting fingers. Slit lamp biomicroscopy revealed severe corneal haze accompanied by non-specific endothelial precipitates following an acute inflammatory response. Mild inflammation could be detected in the anterior chamber. Moreover, the re-epithelialization process could barely be detected. His corneal state gradually deteriorated, resulting in descemetocele and finally perforation.</p> <p>Conclusion</p> <p>In this report, we present a case of a patient with corneal melting after standard corneal collagen cross-linking treatment for keratoconus corneas following an acute inflammatory response. Despite modifying postoperative treatment, elaboration of all apparent associated causes by the treating physicians and undergoing extensive laboratory testing, the patient developed descemetocele, which led to perforation. Our report suggests that further research is necessary regarding the safety of corneal collagen cross-linking in keratoconus corneas.</p

A Constant-Force Technique to Measure Corneal Biomechanical Changes after Collagen Cross-Linking

PurposeTo introduce a constant-force technique for the analysis of corneal biomechanical changes induced after collagen cross-linking (CXL) that is better adapted to the natural loading in the eye than previous methods.MethodsFor the biomechanical testing, a total of 50 freshly enucleated eyes were obtained and subdivided in groups of 5 eyes each. A Zwicki-Line Testing Machine was used to analyze the strain of 11 mm long and 5 mm wide porcine corneal strips, with and without CXL. Before material testing, the corneal tissues were pre-stressed with 0.02 N until force stabilization. Standard strip extensiometry was performed as control technique. For the constant-force technique, tissue elongation (Δ strain, %) was analyzed for 180 seconds while different constant forces (0.25 N, 0.5 N, 1 N, 5 N) were applied.ResultsUsing a constant force of 0.5 N, we observed a significant difference in Δstrain between 0.26±0.01% in controls and 0.12±0.03% in the CXL-treated group (p = 0.003) over baseline. Similarly, using a constant force of 1 N, Δstrain was 0.31±0.03% in controls and 0.19±0.02% after CXL treatment (p = 0.008). No significant differences were observed between CXL-treated groups and controls with 0.25 N or 5 N constant forces. Standard stress-strain extensiometry failed to show significant differences between CXL-treated groups and controls at all percentages of strains tested.ConclusionWe propose a constant-force technique to measure corneal biomechanics in a more physiologic way. When compared to standard stress-strain extensiometry, the constant-force technique provides less variability and thus reaches significant results with a lower sample number

Recent Innovations in Collagen Corneal Cross-linking; a Mini Review

The introduction of corneal cross-linking (CXL) with ultraviolet-A (UVA) and Riboflavin photosensitizer (Vit B2) from Seiler et al., revolutionized the treatment of Keratoconus and other corneal ectatic diseases. Today, the commonly known epithelium off Dresden protocol is in clinical use for the last 15 years with great success and regarded by many as the golden standard