Abstract
Purpose:
To assess the relationship between intraocular pressure (IOP) increase induced by microvolumetric changes and corneoscleral biomechanical characteristics in the human eye.
Methods:
Five human eyes were tested within 12 hrs postmortem. Corneal properties were first examined using a quantitative A-mode ultrasound method (He and Liu, IOVS 2011,52(2)). The globes were then perfused to establish a baseline IOP of 15mmHg. 15 μL of PBS was infused at a rate of 15, 1 or 0.1 μL/s using a syringe pump (PHD Ultra, Harvard Apparatus) to induce an IOP increase. IOP was monitored using a pressure sensor (P75, Harvard Apparatus) at a sampling rate of 20Hz and the maximal increase in IOP (ΔIOP) during the infusion was recorded. The sclera shells were then prepared and clamped to a custom-built chamber for inflation testing from 5 to 30 mmHg after preconditioning. The strains along the meridian direction in the temporal superior (TS), temporal inferior (TI), nasal superior (NS), and nasal inferior (NI) regions of the posterior sclera were measured using ultrasound speckle tracking (Tang & Liu, J Biomech Eng 2012, 134(9)). Creep tests at 30 mmHg were also performed at all four quadrants. The relationships between corneal and scleral parameters and ΔIOP were evaluated using Pearson correlation coefficients.
Results:
The average ΔIOP in donor eyes (age = 53 to 75 yrs) was 19.6 ± 3.6, 18.3±3.9 and 15.2±2.2 mmHg at 15, 1 and 0.1 μL/s infusion rates. The radial and tangential strains in the posterior sclera were -1.4±-0.3% and 0.4±0.4% (NI), -1.1±-0.7% and 0.2±0.2% (NS), -0.8±-0.4% and 0.3±0.2% (TI), and -1.0±-1.0% and 0.3±0.1% (TS) at an inflation pressure of 20 mmHg. The average radial strain at 10 minutes of creep was -2.4±-1.0%, while minimal tangential strains were detected during creep. A trend of positive correlation was found between ΔIOP (at 15 μL/s infusion) and central cornea thickness (p=0.03) and the radial strains during creep (p=0.05). No other significant correlations were found in the current study.
Conclusions:
Corneoscleral biomechanics may play an important role in modulating IOP-associated glaucomatous damage.This study indicated a potential link between corneoscleral biomechanics and IOP dynamics in the human eye and this result motivates further studies with a larger sample size.
Keywords: 708 sclera •
568 intraocular pressure