Induction of Elevated Intraocular Pressure in a Rat Model

Take an anesthetized rat and measure the intraocular pressure, or IOP, in both the experimental and control eyes.

The IOP reflects the balance between aqueous humor production by the ciliary bodies and its drainage through the limbal blood vessels located between the cornea and sclera.

Under a microscope, clamp the experimental eye to expose the limbal blood vessels.

Use an ophthalmic cautery, a heat-generating device, to seal the vessels around the corneal circumference.

The appearance of circular marks and pupil dilation indicates successful cauterization.

The heat coagulates the connective tissue proteins in the blood vessel walls, forming a plug that impairs the aqueous humor outflow and raises the IOP.

Measure the post-operative IOP to assess the elevated pressure in the experimental eye compared to the control eye.

To measure baseline intraocular pressure, or IOP, of both experimental and contralateral control eyes, place the anesthetized rat in a ventral decubitus position on the benchtop, such that the corneal surface is easily accessible to the tip of the tonometer. Position the tonometer tip such that it slightly touches the central corneal zone perpendicularly. Then, acquired the measurement by pressing the measurement button.

Next, place the rat in a slight lateral decubitus position under a stereomicroscope, and inspect the experimental eye at 40 times magnification. During the procedure, keep the contralateral control eye lubricated by instilling a drop of carmellose sodium, or sodium hyaluronate.

Next, using curved forceps, gently push the experimental eyeball forward to expose the vasculature surrounding 360 degrees of the limbus. Then, with the other hand, using a low temperature ophthalmic cautery, gently cauterize the vessels all around the cornea. Be careful not to cauterize the corneal periphery.

Confirm the success of the surgical procedure by observing the emergence of small circular marks of cauterization on the scleral limbus, the obliteration of limbal vasculature, and pupil dilation in the operated eye. After the surgery, check the immediate postoperative IOP in both eyes, as demonstrated earlier.

Then apply a drop of ophthalmic prednisolone acetate to the anterior surface of the experimental eye. After 40 seconds, replace it with an ophthalmic antibiotic ointment. Apply a daily clinical follow-up of the experimental eye with topical medications composed of a non-steroidal anti-inflammatory drug and antibiotic ointment.