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DB Denham, V Fernandez, C Billotte, A Rosen, P Lamar, F Manns, A Ho, P Erickson, JM Parel; Method For Ex-vivo Assessment Of Accommodation Forces . Invest. Ophthalmol. Vis. Sci. 2002;43(13):403.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To measure forces occurring during simulated accommodation in cadaver eyes. Method: A stretching device similar to the ones designed by Fisher, Campbell and others, but also allowing force measurements, was built to apply circumferential loads to the zonular apparatus of cadaver eyes to simulate the accommodation mechanism. Eight PMMA segments ("shoes") are attached to the sclera of the cadaver eye posterior to the limbus. The posterior hemisphere, vitreous, cornea and iris are removed and 8 radial scleral incisions are made between the "shoes" to the level of the choroid. The tissue section including the lens, zonules and ciliary body is mounted in a chamber filled with isotonic solution that allows observation through the operation microscope and coaxial fiberoptic retroillumination. Each of the eight shoes is connected to a T-shaped bar by suture lines using a system of hooks and pulleys. The bar is moved by a programmable computer controlled stepper motor at a speed of 0.1-10mm/s. A computer-controlled load cell mounted on the bar records the total radial load during stretching. Elongation of the ciliary body, zonules and lens are subsequently measured on video images. A silicone annulus is used as a daily calibration standard. Preliminary testing was performed in human and non-human primate eyes with displacements ranging from 0 to 4 mm. Results: Repetitive testing with the silicon ring shows that the repeatability of load-displacement curves is 1% during continuous testing and 4% from day to day. Tests with calibrated weights show that the accuracy of the load cell system is ±10mg. Preliminary tests show that the load displacement curves of Eye-Bank eyes are approximately linear with a load of approximately 5g for a 2mm increase in ciliary body circumferential diameter. Conclusion: Mechanical forces occurring during accommodation can be assessed ex-vivo. Support: Henri and Flore Lesieur Foundation; Florida Lions Eye Bank; Research to Prevent Blindness, NY; Australian Cooperative Research Centre (CRC) Scheme, CRC for Eye Research and Technology, Sydney.
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