Intravitreal Injections in the Ovine Eye

Intravitreal injections can be used to deliver therapeutic agents to the retina. A protocol for intravitreal injections into the sheep eye, as a model of the human eye, is presented here. Intravitreal injections are much less invasive than other ocular injections.

Intravitreal injections can be successfully used to deliver a gene therapy product and treat retinal degeneration in sheep with naturally-occurring neuronal ceroid lipofuscinoses. Once the sheep is anesthetized, start aseptically disinfecting the eye to be injected by irrigating it with 1 to 5%povidone iodine solution using a 20-milliliter syringe. Then, position a sterile, fenestrated surgical drape over the eye.

Fit an eye speculum to the eyelids to hold the eye open. Grasp the bulbar conjunctiva on the dorsal lateral aspect of the eye with forceps and rotate the eye globe ventromedially. Insert the needle approximately seven-millimeter posterior to the sclera on the lateral aspect of the eye, and angled posteriorly to avoid the lens.

Administer the single injection of 100 microliters as a bolus, as close to the retina as possible, without disturbing the retinal surface. Rinse the eye with approximately 10 to 15 milliliters of 1 to 5%povidone iodine solution followed by 10 milliliters of saline, before removal of the speculum and drape. Electroretinography analysis demonstrated preserved retinal function in the treated eye while the untreated eye declined in a similar manner to CLN5-affected animals.

Retinal histology was near normalized in the treated eye with a total retinal thickness comparable to healthy control animals in the central retina. In contrast, the thickness of the untreated retina was comparable to CLN5-affected animals. The expression of the glial fibrillary acidic protein, or GFAP, a marker of retinal stress and astroglia, was lower in treated eyes than the untreated eyes, indicating that disease-associated inflammation was attenuated following treatment.

With the establishment of a protocol for intravitreal injections into the sheep eye, sheep could now be used to test the safety and efficacy of many intravitreally-delivered therapeutic agents.