This study was performed by three

researchers named B K Pierscionek, M Asejczyk-Widlicka, and R A Schachar. This study

was done to figure out the effects of IOP when the cornea and sclera were

deformed. The authors wanted to

specifically see how the corneal and scleral radii reacted to IOP. They

deformed the cornea and sclera by injecting through the optic nerve to the

vitreous. Then they measured the IOP and ocular rigidity after the deformation.

The final conclusions of this study were that the elastic moduli of both the

cornea and sclera are independent of IOP. Some differences in results between

the cornea and sclera are that the modulus of elasticity of the sclera is

higher than the modulus of elasticity in the cornea and the curvature of the

sclera changes when IOP increases while the curvature of the cornea does not

change with increasing IOP. Lastly, it was seen that the porcine scleral

rigidity seemed to be similar to the human scleral rigidity.

The authors were able to obtain 16

porcine eyes to use in their experiments. Since they are eyeballs they need to

stay fresh so the authors kept the eyes on ice as they transported them and

then during the preparation and experiment the authors kept the eyes moist by

putting saline solution on them. Also, the extraocular muscles and extraneous

fat were removed from the eyeballs. In

order to keep the eyes in one position the authors placed the eyeballs on a

base that was made of perspex tubing with gradation along the edge. The radii

for the corneal and scleral profiles were measured by the authors taking pictures

of the eyeball and then uploading the pictures onto a computer. In order to

find the center of curvature of each eyeball the authors had to use an

optimization procedure. By using a corneal applanation tonometer, that had an

accuracy of plus or minus 2 mm the authors were able to figure out the baseline

IOP.

In order to be accurate the authors

measured the IOP four different times after each of the 5 injections of 100 ul

increments were injected into the vitreous. The authors were also able to

measure the ocular rigidity from this as well. By using equations applicable to

thin-walled pressure vessels the authors were able to measure the elastic

properties of the cornea and sclera. The assumption to allow us to apply these

equations to the eyeball was that the authors had to treat the eyeball as a

thin-walled pressure vessel. One equation that we did not go over in class that

was used is the equation for circumferential stress, which is P times R divided

by 2 times t. The variables are as follows:

P is the IOP, R is the radius of the scleral shell, and t is the

thickness of the scleral shell. The authors also used an equation for

volumetric strain within a thin- walled sphere which is 3 divided by E, which

is the elastic modulus, all multiplied by stress minus Poisson’s ratio (for the

sclera) which is then multiplied by stress. They then use the volume of the eye

and the equation for volumetric strain to derive an equation for elastic

modulus, which ends up being 3 times 1 minus Poisson’s ratio all multiplied by

stress over volumetric strain.