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J-M Parel, V Fernandez, C Billotte, DB Denham, PD Lamar, A Rosen, A Ho, N Kenyon, BR Collins, P Erickson; Accommodation Stress-Strain Relation in Human and Non-Human Primate Eyes Ex-Vivo . Invest. Ophthalmol. Vis. Sci. 2002;43(13):406.
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Purpose: To measure the stress-strain relation during ex-vivo simulated accommodation. Methods: Based on designs by Fischer, Campbell, Sunderland, and Glasser, a computer controlled stretching system was constructed to apply a circumferential load to the zonular apparatus of cadaver eyes immersed in an optical cell while continuously recording the load-elongation curves. The recorded curves are superimposed on a videorecording of the eye section viewed through the operation microscope. Pinhole retroillumination permits qualitative assessment of lens power changes during stretching. The system was designed to permit open lens surgery, including lens-refilling procedures (Phaco-Ersatz). The crystalline lens of 6 cynomologous (4 year old) and 2 human (14 years old) eyes (3 hrs to 5 days postmortem) underwent pre and postoperative testing for up to 4mm increase in circumferential diameter. Differential elongation of the ciliary body, zonules and lens were subsequently measured on video images. The natural or refilled lens weight and volume were measured by shadow-photogrammetry. Results: Preoperatively, the load-elongation curves are quasi-linear and very similar in both the cynomologous and human eyes, with a load of approximately 10g for a 4mm diameter increase. The image of the pinhole by the lens was defocused in all experiments, which qualitatively demonstrates changes in optical power during stretching. Similar results were obtained with empty capsular bags and bags refilled with low consistency polymeric gels. Ciliary body breaks occurred at loads of 13 to 20g corresponding to extensions larger than 4mm. Larger extensions slightly increased the size of the capsulorhexis but did not cause zonular breakage or a capsule tear. Repeating the stretching cycles gave reproducible results with loads smaller than 5gr. Conclusion: This pilot study confirms that young non-human primate eyes are a good model for young human eyes and can be used to assess ex-vivo the natural accommodation and its surgical restoration. 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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