Mechanical Properties of Human Lens Capsule Assessed Ex Vivo in a Lens Stretcher

Abstract

Purpose: : To determine the mechanical properties of the human natural lens in a lens stretcher before and after removal of the lens contents.

Methods: : Postmortem human eyes (n = 91, Age = 1 day to 76 yrs, PMT = 15 to 120 hrs) obtained from the Ramayamma International Eye Bank in India & several Eye Banks in USA were dissected according to a protocol described previously (Manns et al, IOVS 2007) to produce specimens that contain the lens maintained in its accommodating framework, including intact zonules and, ciliary body and 8 sections of sclera. The specimens were mounted in a mechanical lens stretching system (Parel et al, ARVO 2002) and the ciliary body was stretched 2 mm radially in increments of 0.25 mm. The load and lens equatorial diameter were measured at each step. The lens contents were removed through a small peripheral capsulorhexis (1.2 mm, range 0.7 mm to 2 mm) (Tahi et al, JCRS 1999). The stretching cycles were repeated on the empty capsular bag (Ziebarth et al, IOVS 2008). The load-diameter relationship was analysed as a function of age.

Results: : The unstretched empty lens capsule diameter increased with age (in mm: 9.24 + 0.01*Age, p<0.0001) between ages 6 and 76 yrs. Removal of lens contents increased lens capsule diameter by 6.5 ± 3.0% independent of age (p = 0.11). The load necessary to stretch the empty lens capsule was independent of age (15.3 ± 4.9 g/mm, p = 0.20). The ratio of load-diameter slopes for the empty bag and the natural lens decreased significantly with age (0.82 - 0.01*Age, p<0.0001).

Conclusions: : There was no difference between Indian and US lens capsules. Over the age range examined, the stiffness of the human lens capsule is constant. With aging, the lens contents require a greater force to stretch.

Keywords: aging • accommodation • presbyopia