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H. Aliyar, P. Hamilton, M. Fetsch, N. Ravi; Viscoelasticity of Lens Capsular Bag Filled by in-situ Formed Hydrogel . Invest. Ophthalmol. Vis. Sci. 2003;44(13):243.
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Purpose: Age-related changes in the viscoelasticity of the lens have been implicated to be one of the primary causes of lenticular presbyopia; however, the viscoelastic constitutive equation of the lens is unknown and needs to be determined. A custom-designed radial stretcher capable of performing stress-strain experiments in physiological mode was used. To validate the experimental technique, hydrogels of known mechanical properties were formed within pre-evacuated lens capsular bags. Methods: Copolyacrylamide solutions (5-20%) were used to form cylindrical hydrogels and their mechanical properties were determined by compression between parallel plates. The same solutions were used for endocapsular gelation. Fresh pig eyes were used. The cornea and iris were dissected. A capsulorhexis of ~1.0 mm in diameter on the lens was performed using an Ellmen surgitron. The capsular bag was then evacuated with a Storz phacofrag instrument. Copolyacrylamide of select compositions and concentrations were used to fill the evacuated lens capsular bag, which formed hydrogels inside the capsular bag within a few minutes. The radical stretcher, a mechanical analogue of ciliary body, was used to carry out the stress-strain experiments. Results: The moduli of the hydrogels ranged from 300 to 2000 Pa and were a function of composition and concentration. We successfully performed the capsulorhexis and injected the polymer solution into the capsular bag where it gelled in less than five minutes. The stress-strain characteristics of the lens capsule-hydrogel (10 wt.%; molecular weight of 350,000 daltons; modulus 1500 Pa) composite were similar to that of the natural lens as shown in the figure. The hydrogels were optically clear, mechanically soft, and objects seen through the lens appeared undistorted. Conclusions: This method provides a validating technique to gain insight into the viscoelasticity of the lens. The procedures developed thus far also aid us in our continuing pursuit of developing an accommodating intra-ocular lens. View OriginalDownload SlideView OriginalDownload Slide
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