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Corneal Stiffness Affects IOP Elevation during Rapid Volume Change in the Eye

¹From the Departments of Biomedical Engineering and ²Ophthalmology, The Ohio State University, Columbus, Ohio.

PURPOSE. To investigate whether corneal stiffness affects the elevation of intraocular pressure after an acute increase in the volume of ocular fluid.

METHODS. Saline (200 µL total) was infused into porcine globes before and after corneal stiffening. Intraocular pressure (IOP) was continuously monitored by a pressure sensor that was cannulated to the vitreous chamber. Corneal stiffening was achieved by immersing the corneas in a 1% or 4% glutaraldehyde solution for 20 minutes. Corneal strips were dissected from the globes, and the stress-strain relationships were measured. The mean secant modulus of each group of corneas at 5% strain was calculated. Control eyes with no corneal stiffening were also tested.

RESULTS. A significantly higher IOP elevation was observed in the globes after the corneas were stiffened (mean ± SD, 14.9 ± 1.9 mm Hg before stiffening vs. 19.1 ± 2.6 mm Hg after 1% glutaraldehyde treatment and 24.3 ± 1.9 mm Hg after 4% glutaraldehyde treatment at 200 µL infusion; P < 0.001). The control group showed no change in IOP elevation. The 5% secant modulus was 0.46 ± 0.24 MPa, 1.63 ± 0.41 MPa, and 2.78 ± 1.04 MPa (mean ± SD), respectively for the original corneal tissue and tissue with 1% or 4% glutaraldehyde treatment.

CONCLUSIONS. This study showed that stiffened corneas induced substantially higher IOP elevations when all other geometrical and material properties of the eye remained essentially the same. The results suggested that corneal stiffness may play an important role in determining IOP elevation caused by an acute increase in the volume of intraocular fluid.