Elastic Properties of Whole Cadaver Primate Crystalline Lenses Assessed by Atomic Force Microscopy

Abstract

Purpose:: To compare humans and non-human primate cadaver lens elasticity using atomic force microscopy (AFM).

Methods:: AFM elasticity measurements were performed on intact lenses of 18 non-fixed cynomolgus eyes (4-10 years, <1 day postmortem) and 8 non-fixed human eyes (26-82 years, <3 days postmortem) that were left attached to the zonule-ciliary body-sclera framework. The eyes were prepared by bonding a plastic ring on the sclera after removal of conjunctiva, adipose, and muscle tissues. The posterior pole was sectioned and excess vitreous was removed but the anterior vitreous and hyaloid membrane were left intact. The eye’s anterior section was placed on a Teflon slide to protect the posterior pole of the lens, and the cornea and iris were sectioned. The lens-zonule-ciliary body-sclera section was then placed in a Petri dish filled with DMEM in a laboratory-built AFM system designed for force measurements (Wojcikiewicz et al, J Cell Science, 2003). The central pole of the anterior lens surface was probed with the AFM cantilever tip. The recorded cantilever deflection-indentation curves were used to derive force-indentation curves for the lens. Young’s modulus was calculated from the force-indentation relation using the model of Hertz (Timoshenko, Theory of Elasticity 1934).

Results:: Young’s modulus was ranged from 0.4 to 3.2kPa for monkey eyes and 0.8kPa-29.4 MPa for human eyes. Measurements from 4 human eyes were excluded due to capsular delimination. Young’s modulus was found to increase significantly with age (p=0.06).

Conclusions:: Pre-presbyopic cynomolgus monkey and human lenses have comparable elasticity. The elasticity of both human and monkey lenses increases with age.Support: NSF Graduate Student Fellowship; NIH EY14225; Florida Lions Eye Bank; Vision CRC, Sydney Australia;AMO Inc, Santa Ana, CA;NIH center grant P30-EY014801; Research to Prevent Blindness.; Henri and Flore Lesieur Foundation; NSF-BITC; NIH GM55611; Scientific Advisory Committee, University of Miami.

Keywords: presbyopia • aging