Dioptric Power vs Zonular Tension During Ex-vivo Simulated Accommodation of Primate Crystaline Lenses Before and After Refilling

Abstract

Abstract: : Purpose:: To assess the force vs dioptric power relationship in natural and refilled lenses of non-human primates cadaver eyes in a lens-stretching device. Methods: An 8-segment lens stretcher (EVAS, presented at ARVO'02) equipped with a load sensor was used to radially stretch 4 cynomolgus monkey cadaver lenses (postmortem time: 2h to 4days, 2 y/o). Specimens comprising the lens, capsule, zonule, ciliary body and segmented sclera were prepared by bonding PMMA segments to the anterior scleral surface; excising the cornea, iris, posterior pole and adherent vitreous; and segmenting the sclera between each PMMA segment. The specimens were immersed in the EVAS cell filled with DMEM solution and stretched radially by up to 2 mm, in 0.5 mm steps. An optical system using the Scheiner principle was used to measure changes in lens focal length during stretching. The optical system delivered 2 parallel beams (0.1mm dia, 3mm separation) to the specimen along the optical axis of the lens. The point of convergence of the two beams after passing through the specimen was detected using a CCD camera mounted on a translation stage. Optical calculations were used to calculate the corresponding change in crystalline lens power. After testing the crystalline lens in its natural state, the capsular bag was emptied and refilled with a polymer (phaco-ersatz surgery). Refilled lenses were tested before and after polymer crosslinking. Results: Lens refilling in the stretcher was successful in 3 out of 4 lenses. The lens power before and after refilling decreased linearly as the load increased. The slopes of the linear regression for the four eyes before and after refilling were, in Diopters/gram: -3.17/-4.32, -1.90/N/A, -1.87/-0.85, and -4.32/-1.25. The powers of the four lenses at 0 load before and after refilling were, in Diopters: 42.0/38.2, 46.3/N/A, 33.4/35.1, and 38.2/21.2. Conclusions: This study demonstrates that the ex vivo accommodation system can be used to compare the accommodation amplitude and force of natural and refilled lenses. CR: NONE. Support: NIH Grant#EY14225-01; Australian CRC Scheme, CRC for Eye Research and Technology, Sydney; Florida Lions Eye Bank; Henri and Flore Lesieur Foundation; Research to Prevent Blindness.

Keywords: accommodation