PMC

Specimen in the inflation testing fixture. The inset depicts a close-up of the tissue sample in the holder, with the cannula angled slightly to avoid the lens and to properly insert into the anterior chamber.

The averaged creep response of the 2 and 11 month old C57BL/6 scleral tissue to elevations in pressure. The younger tissue showed evidence of pressure-dependent creep, where the older tissue did not. The associated creep rates are reported in .

Sclera inflation displacement profiles following tracking points from the limbus (testing fixture) to the apex for a typical 2 month old C57BL/6 sclera in the A) x-direction B) y-direction, and a typical 11 month old C57BL/6 sclera in the C) x-direction D) y-direction. Profiles are taken at 10.5, 15, 22.5, 30, 37.5, and 45mmHg.

The averaged apex displacement, representing an average of two points from the peripapillary region for each specimen, comparing the 2 and 11 month old C57BL/6 scleral tissue for A) the first loading ramp from 6 to 15mmHg and B) the last loading ramp from 6 to 45mmHg. Age has a significant stiffening effect to the structural response of the inflating mouse sclera.

A digital image correlation (DIC) video snapshot of a 2 month old C57BL/6 mouse sclera in the testing fixture underneath the dissecting microscope in the reference configuration. The boxes represent the digital image correlation (DIC) tracking subset locations for 2D tracking of the point relative to its position in the reference configuration, and the numbers indicate the location for fresh-tissue scleral thickness measurements. The optic nerve is excised approximately 2 mm behind the eye and left in place during testing. The apex tracking location is immediately on the nasal and temporal side of the optic nerve, and DIC measurements are made in locations every 100 micrometers from there toward the fixture attachment at the limbus.

Experimental set-up. The eye is tested in a PBS bath and its IOP is measured and controlled via an active pressure-feedback controller through the attached cannula. The pressure of the sample is recorded on a computer (Dell Precision T7500) through a National Instruments data acquisition system (NI 9237 DAQ). The automated syringe pump (Cavro XL 3000, 5mL) is programmed, through a Labview proportional controller (National Instruments, V8.5), to dispense or aspirate PBS into the cannula depending on the difference between the measured pressure (P_actual) and the set pressure (P_set). The CCD video camera (GRAS-20S4M/C, Pt. Grey Research) attached to the dissecting microscope (Zeiss Greybody) records images during inflation testing, and the digital image correlation software (Vic 2D, Correlated Solutions) measures scleral displacement.