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

Support for ITER ECRF design. Substask 3 Design and optimzation of the window unit. Final Report

The proposed ITER ECH window unit employs a single, edge-cooled (water, e.g. 20 C) CVD-diamond disk in a corrugated HE_1_1 waveguide with 52 mm inner diameter, with an outer disk diameter of 77 mm and a thickness of 1.482 mm (4 #lambda#/2). Thermal computations show that for larger outer disk diameters the peak temperature is unaffected. Thus due to the high thermal conductivity of the diamond, the exposed window edge area does not have to be large to obtain significant heat transfer. This implies that the window diameter can be minimized which has the added benefit of reducing the cost. For a power of 1 MW at 170 GHz, a loss tangent of 1.10"-"5, a thermal conductivity of 1800 W/mK (at room temperature) and a heat transfer coefficient of 12 kW/m"2K (water flow: 13.5 1/min, water velocity: 2 m/s, room temperature) to the cooling water the central window temperature will not be higher than approx. 45 C and the edge temperature is about 30 C. The absorbed power is 176 W. Simulations also show that steady state conditions are generally achieved in under 3 s and that a 2 MW window should be feasible. Owing to the negligible temperature dependence of the CVD-diamond loss tangent, also the approximately 100 C hot torus cooling water could be used to cool the window. Simulations of an ''encased'' window, a window in which the edge of the disk has been covered with a 0.4 mm thick layer of electrodeposited copper (tritium barrier in case of broken window disk), show that this is feasible without a significant decrease in heat transfer rate. Neutron irradiation tests were extended to fluences of 10"2"1 n/m"2 (E > 0.1 MeV)17 refs.Available from TIB Hannover: ZA 5141(6255) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman