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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.

Clinical Signs

Enlargement of the eye


  • History
  • Clinical signs
  • Eye exam
  • Tonopen or Tonovet - Measurement of intraocular pressure

Reported Cases

  • Case 1: Glaucoma in a Owl A captive-bred adult great horned owl behaved as though it was bilaterally blind. An ophthalmological examination showed that it had an increased intraocular pressure in both eyes and gonioscopy showed an abnormality of the iridocorneal angles. Retinal changes were also observed. Treatment was not attempted and the owl was euthanased. Histopathology confirmed the abnormal iridocorneal angles, but the exact aetiology of the primary glaucoma was not identified. Ref

  • Case 2: Glaucoma in a White-bellied caique A 34-day-old, male, white-bellied caique was presented for a complaint of bilateral buphthalmos. Clinical examination was unremarkable apart from the ophthalmic findings. The ophthalmologic examination was negative for direct, consensual, and dazzle reflexes in both eyes. The intraocular pressure exceeded 40 mm Hg OU. Fluorescein stain demonstrated corneal surface lesions suggestive of exposure keratopathy subsequent to bilateral buphthalmos. Diagnostic imaging tests were conducted to perform ocular biometric measurements and investigate the intraocular structures, including the iridocorneal angle and lens, by means of high-resolution ultrasonography (HRUS). The presence of congenital glaucoma in this young parrot was strongly suspected after clinical and ophthalmological examination and the results of diagnostic imaging. Pharmacological treatment to reduce intraocular pressure was initiated using dorzolamide hydrochloride 2% and timolol maleate 0.5%. A month later, the parrot's eyes did not show any visual improvement, but the intraocular pressure had returned to normal. The parrot was unable to feed itself and died during a feeding procedure. Postmortem examination revealed ab ingestis pneumonia. Both eyes were submitted for histopathology, with severe anterior segment dysplasia and goniodysgenesis found OU. Histological findings added to the clinical presentation, the ophthalmologic examination and the imaging findings, confirmed the presence of congenital glaucoma. Ref


Topical dorzolamideA type of carbonic anhydrase inhibitor that is applied two to three times a day initially, then titrated to effect (which may take up to 4 or 5 days).
Osmotic agentsMannitol, glycerin or isosorbide.
SurgeryEnucleation (eye removal) surgery, while under general anesthesia.



Reduce risk of trauma

Scientific References

Risk Factors

  • Prior history of trauma to the eye

Case Stories