Glaucoma is a group of eye conditions leading to the interruption of visual information from the eye to the brain. In most cases of glaucoma, an increased pressure in the eye, commonly known as intraocular pressure (IOP), causes damage to the optic nerve via retinal ganglion cell (RGC) apoptosis. Chickens can develop glaucoma as a primary condition or secondary to trauma. Glaucoma needs to be differentiated from other causes of exophthalmos (a bulging or enlarged eye).
How is glaucoma diagnosed?
For a definite diagnosis of glaucoma, your veterinarian will need to measure the intraocular pressure (IOP) within your chicken's eye. This is accomplished through the use of a handhold tonometer. A normal bird's eye will have an intraocular pressure between 9.2 and 22 mmHg.
How is glaucoma treated?
The major treatment for glaucoma consists of lowering the IOP through eye drops, oral drugs, and sometimes surgery. Some of the common drugs used for glaucoma therapy include:
- Osmotic agents: This are known for producing rapid results, and as such are most frequently used during emergency management of glaucoma. The most commonly drugs used in animals include mannitol, glycerin and isosorbide. They are administered systemically and distributed to extracellular fluids, increasing plasma osmolality.
- Carbonic anhydrase inhibitors (CAIs): These are known for their ability to inhibit the formation of bicarbonate in the ciliary body that is necessary for aqueous humor production. The most commonly used topical agents include dorzolamide and brinzolamide. CAIs are shown to be very effective in dogs and cats.
- Beta-blockers: These are known for being highly effective in humans, and as such as the most commonly prescribed for treatment in people. They have been increasingly used for glaucoma treatment in animals, especially horses. Timolol is the most commonly used drug. Other topical beta-blockers include levobunolol, betaxolol, metipranolol and carteolol.
When the condition has advanced, surgery to remove the eye may be needed.