Age-dependence of mouse lens viscoelasticity

Abstract

Purpose : Prior studies using compression testing suggest the mouse lens becomes stiffer with age, but the age-dependence of mouse lens viscosity has not been characterized. The purpose of this study was to measure and compare the viscoelasticity of young and old mice by quantifying their response during compression and stress relaxation.

Methods : Data were acquired on 10 young (8 weeks old) and 10 old (8 months old) C57BL/6J mouse lenses. Lenses were extracted from the eye and incubated (Garner & Garner. IOVS 2016;57:2851-2863) in a solution of Dulbecco's Modified Eagle Medium (DMEM) and 1% antimycotic at 37°C for 18 hours. Following the incubation, the lenses were placed in a DMEM-filled chamber within a custom-built elastometer system (Figure 1). The elastometer compresses the lens using a 4mm diameter cylindrical probe connected to a load sensor mounted on a computer-controlled positioning stage. The elastometer includes an imaging system that continuously records bottom and side views of the lens during experiments. The lens was compressed by 600µm at a speed of 48.6µm/s and the probe was held at the final position for 5 minutes. The load was recorded during the compression and stress relaxation phases. The experiment was performed a total of 3 times on each lens, with a resting period of 6 minutes between compressions. All lenses were imaged pre- and post-compression using SD-OCT to ensure the capsule remained intact (Figure 2). Lens stiffness in g/mm was estimated from linear fits of load-displacement data recorded during the first 250s of the compression phase. The relaxation phase was fit with a three-term exponential series. The time constants (t1, t2, t3) and asymptotic load (F) were quantified from the fit. The stiffness, time constants and asymptotic load of young and old mouse lenses were compared.

Results : The stiffness of the young and old lenses were 1.16±0.11g/mm and 1.35±0.14g/mm, respectively. The three time constants were t1 = 223.2±5.7s, t2 = 25.0±1.3s, t3= 3.2±0.6s for the young lenses and t1 = 192.2±5.4s, t2 = 22.2±0.8s and t3 = 2.5±0.1s for the old lenses. The asymptotic loads for the young and old lenses were 1166.6±22.5mg and 1180.0±15.5mg, respectively. The linear fit (stiffness) and time constants were statistically different (p<0.05) between the young and old mouse lenses.

Conclusions : Old mouse lenses are stiffer and less viscous (faster stress relaxation time) than young mouse lenses.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.