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X. He, J. Liu; Stiffened Cornea Is Associated With Higher IOP Elevation. Invest. Ophthalmol. Vis. Sci. 2008;49(13):697.
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The Ocular Hypertension Study had reported central corneal thickness as a powerful predictive factor for glaucoma progression (Gordon, 2002). However, the mechanistic details of the cornea’s role in glaucoma are not well understood. The goal of the current study is to investigate whether corneal stiffness affects the eye’s ability to regulate IOP after an acute increase of intraocular fluid.
Ten fresh porcine globes were obtained within 2h postmortem. The corneas were dehydrated in 20% dextran solution to resume a normal thickness. An 18G needle was inserted from limbus into the vitreous chamber, and was connected to a 3-way valve via rigid tubing. The valve was connected to an injection syringe and a pressure sensor that monitored the IOP continuously (calibrated prior to experiments). The initial IOP for all eyes was adjusted to 10 mmHg. The original corneal stiffness was measured by a non-invasive ultrasound technique developed in our laboratory (Liu, 2007). 0.2ml saline was infused into the eye in 1 min. The peak value of IOP during infusion was recorded. After saline injection, the IOP was allowed to resume 10 mmHg. The cornea was then immersed in a 5% glutaraldehyde solution (with 15% dextran) for 20 min. Glutaraldehyde was proven to stiffen the corneas by introducing collagen crosslinking. The eye was facing down and only the cornea surface was immersed in the solution. The same saline infusion was repeated after the crosslinking treatment in the same eye, and the peak IOP was recorded. The ultrasonic measurement was repeated in the same eyes after the corneas were stiffened.
The measurements from the ultrasound method showed a significant increase in corneal stiffness after glutaraldehyde treatment (2.45 ± 0.04 GPa before treatment vs. 2.55 ± 0.03 GPa after treatment, P<0.0001). We found a significantly higher IOP elevation after the corneas were stiffened (15 ± 3 mmHg before stiffening vs. 33 ± 5 mmHg after stiffening, P<0.0001).
The results suggested that corneal stiffness plays an important role in regulating IOP elevation caused by an increase of the volume of the intraocular fluid. Our results showed that a stiffened cornea was associated with much higher IOP elevation in the same eye. This indicated that corneal stiffness could be an important risk factor for glaucoma.Reference:Gordon, M.O., et al., The Ocular Hypertension Treatment Study - Baseline factors that predict the onset of primary open-angle glaucoma. Archives of Ophthalmology, 2002, 120(6) 714-720.Liu, J., et al., Ultrasonic Model and System for Measurement of Corneal Biomechanical Properties and Validation, Journal of Biomechanics, 2007. 40(5): 1177-82.
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