Glaucoma develops when aqueous humor cannot drain normally, and intraocular pressure rises enough to damage vision-related structures. Glaucoma can be very painful and can permanently damage the retina and optic nerve. The signs of glaucoma in dogs can sometimes appear suddenly, while glaucoma in cats is often associated with another ocular disease. In pets, a red, cloudy eye can be a true veterinary emergency, especially when intraocular pressure is rising. 

Animal Eye Care of New England provides specialty veterinary care for glaucoma in dogs and cats in the Boston, MA area, including diagnosis, pressure monitoring, medical management, and surgical evaluation. Understanding high eye pressure in pets begins with understanding how fluid normally moves through the eye. Veterinary glaucoma treatment options depend on the cause, remaining vision, degree of pressure elevation, and overall condition of the affected eye.

What Is Glaucoma?

Aqueous humor is a clear fluid that supports the eye’s internal structures by delivering nutrients, removing waste, and performing other functions. It also plays a huge role in stabilizing eye pressure. It normally drains through specialized pathways. When drainage is impaired, fluid accumulates, and pressure within the eye can rise.

Glaucoma is very serious. Sustained or severe elevation of intraocular pressure can cause irreversible blindness. The condition can also produce substantial ocular pain.

Pressure can rise rapidly or gradually, depending on the type of glaucoma. An acute increase requires urgent treatment, while chronic disease progresses more slowly. Both forms require veterinary evaluation because vision can decline even when the eye does not initially look severely abnormal.

Why Does Pressure Increase Inside the Eye?

The eye continuously produces aqueous humor, so that fluid needs a way to leave. In dogs and cats, most aqueous humor exits through a drainage region where the iris and cornea meet. This area is called the iridocorneal angle.

When that drainage system becomes restricted, pressure can increase. Structural abnormalities, disease, injury, or infection can cause the problem. Identifying the cause helps the veterinary ophthalmologist classify the glaucoma and plan treatment.

High pressure is dangerous because delicate visual structures are not designed to tolerate sustained pressure elevation. Damage can affect the retina and optic nerve. Vision loss can be permanent. 

Primary and Secondary Glaucoma Are Different

Primary glaucoma develops because of a problem involving the eye’s drainage system. It is particularly important in dogs because several breeds are predisposed. Primary disease affecting one eye also raises concern about the other eye.

Secondary glaucoma occurs when something else, such as injury, medication, or another ocular disease, interferes with aqueous humor drainage. Causes can include inflammation inside the eye, lens displacement, tumors, and other structural abnormalities. 

Treatment must address both the pressure and the underlying problem whenever possible.

Classification affects prognosis and management. A dog with primary glaucoma may need monitoring or preventive treatment of the other eye, while a patient with secondary disease needs evaluation of the condition obstructing drainage. A complete veterinary ophthalmology examination helps distinguish these situations.

Signs of Glaucoma in Dogs

Acute canine glaucoma can cause redness, corneal cloudiness, squinting, a dilated or poorly responsive pupil, vision loss, and obvious changes in the affected eye. Pain can also appear as behavioral changes rather than dramatic rubbing or blinking. You may also notice behavioral changes. Some dogs become quieter, less interested in food, or unusually withdrawn.

With prolonged pressure elevation, the eyeball can enlarge. Chronic glaucoma can also displace the lens and cause permanent structural changes in the eye.

Early signs can be surprisingly subtle. Mild pupil changes, congestion of blood vessels around the eye, and enlargement are easy to miss, especially when only one eye is affected. Regular veterinary exams and pressure measurements are especially valuable for dogs with increased inherited risk.

Glaucoma in Cats Can Be Harder to Recognize

Feline glaucoma is less common than canine glaucoma. We also tend to see secondary glaucoma more often in cats. Inflammation of the anterior uvea and intraocular tumors are common causes, although primary glaucoma can occur. Identifying the cause of the pressure increase is particularly important when evaluating a cat.

Cats may show a dilated or sluggish pupil, redness, corneal swelling or discoloration, and changes in eye size or appearance. Vision may also deteriorate. As in dogs, discomfort may appear through behavior rather than constant squinting.

Your feline companion may hide more, become less social, sleep differently, resist having the face touched, or show reduced interest in normal activities. Those changes are not specific to glaucoma, but they deserve attention when they accompany an abnormal-looking eye. Cats are skilled at masking discomfort so that subtle behavioral changes can offer valuable clues.

Glaucoma Is a Painful Eye Disease

Glaucoma should not be viewed only as a threat to eyesight. Increased intraocular pressure can be painful, particularly during an acute episode. Protecting comfort is a major goal even when vision has already been permanently lost.

Pets do not always express ocular pain in obvious ways. Your animal companion may become quiet, restless, reluctant to eat, less playful, or sensitive around the head. Lethargy and reduced appetite can occur when intraocular pressure increases.

If a pet suddenly seems unwell and one eye becomes red or cloudy, seek prompt veterinary attention. Don’t wait for obvious crying or constant pawing at the face before taking the discomfort seriously. Acute glaucoma is considered an ophthalmic emergency.

How Is Glaucoma Diagnosed?

Tonometry is central to diagnosing glaucoma. A tonometer measures intraocular pressure, allowing the veterinarian to determine whether pressure is abnormally elevated. Modern veterinary practices commonly use rebound or applanation tonometers to obtain these measurements.

Pressure is only part of the examination. The veterinarian also evaluates the appearance of the cornea, pupil, lens, retina, optic nerve, and other ocular structures when they can be visualized. Visual responses and the appearance of the opposite eye provide additional information about the disease.

Tonometry should generally be performed before pupil dilation because dilation can be inappropriate when intraocular pressure is elevated. If glaucoma is identified, additional diagnostic procedures can help classify the disease and evaluate damage. The order of testing matters during a thorough ophthalmic examination.

What Is Gonioscopy?

Gonioscopy allows a veterinary ophthalmologist to examine the iridocorneal angle, the region through which most aqueous humor normally drains. 

This examination can be particularly useful when glaucoma is suspected. Evaluating the opposite eye may provide information about its drainage angle and future risk. The findings can contribute to classification, prognosis, and treatment planning.

Gonioscopy is not the same as measuring eye pressure. Tonometry tells the veterinarian the pressure at that moment, while gonioscopy provides information about the drainage angle anatomy. The two tests answer different questions and can complement one another.

Other Tests May Be Needed

A complete evaluation may include slit-lamp examination, ophthalmoscopy, ocular ultrasound, or other specialized testing, depending on the eye’s condition. The veterinarian may need to investigate inflammation, lens displacement, a tumor, or another disease that could be causing secondary glaucoma. The diagnostic plan is tailored to the findings.

Ophthalmoscopy helps assess the retina and optic nerve when those structures can be seen. As the disease progresses, glaucoma can cause characteristic damage to the optic nerve and retina. Dense corneal edema, cataracts, or other abnormalities can sometimes prevent a clear direct view.

Ultrasound or other imaging techniques can provide information when structures inside the eye cannot be examined normally. The goal is not simply to document elevated pressure but to understand why it developed, whether vision remains, and which treatment approach is appropriate.

Veterinary Glaucoma Treatment Has Several Goals

Treatment aims to lower intraocular pressure, relieve pain, preserve vision when possible, and address the underlying cause of secondary disease. Acute glaucoma requires rapid pressure reduction because continued elevation can damage the optic nerve and retina. Medical and surgical treatments may be used separately or together.

Several classes of ophthalmic medications can reduce aqueous humor production or improve its outflow. The right medications depend on species, glaucoma type, other ocular conditions, and the individual patient’s health. Something that is suitable for one form of glaucoma may not be suitable for another.

A veterinarian must authorize and review all glaucoma medications. Follow the prescribed dose and schedule carefully, and do not use another pet’s eye drops or an old prescription. Glaucoma often requires long-term monitoring because pressure control can change as the disease progresses.

When Is Glaucoma Surgery Considered?

Doctors may consider surgery when medication alone doesn’t control pressure well enough or when preserving remaining vision requires additional intervention. Procedures can target the structures that produce aqueous humor or create another route for fluid drainage. The best option depends on the eye and the type of disease.

Laser procedures can reduce aqueous humor production by treating portions of the ciliary body. Drainage implants can provide another pathway for fluid to leave the eye. These procedures require careful patient selection and continued follow-up because glaucoma remains a progressive disease.

Surgery does not eliminate the need for future monitoring. Pressure can change, and medications may still be necessary. Your veterinary ophthalmologist also needs to evaluate your dog’s vision and comfort over time.

What Happens When a Glaucomatous Eye Is Already Blind?

When blindness becomes irreversible, treatment priority shifts to keeping the animal comfortable. A blind eye with uncontrolled glaucoma can remain painful even though restoring sight is no longer possible. Surgical options for a permanently blind eye may include removal. Although eye removal can initially upset families, the procedure can eliminate a source of chronic ocular pain. Animals often adapt well when a painful, blind eye no longer affects daily comfort. The goal is to make decisions based on quality of life rather than preserving the appearance of an eye that is painful and permanently blind.

Why the Other Eye Matters in Dogs With Primary Glaucoma

Primary glaucoma means both eyes should be monitored, even when only one is experiencing an acute pressure increase. Because inherited drainage abnormalities can affect both eyes, the apparently normal eye may also be at risk. This makes evaluating the opposite eye an important part of the diagnostic process. Monitoring can help identify changes before obvious symptoms develop.

When a veterinary ophthalmologist confirms primary glaucoma, they may recommend gonioscopy, repeated pressure measurements, or preventive medication for the other eye. Recommendations depend on the type of glaucoma and individual findings. 

Follow the prescribed schedule even when the second eye looks completely normal. 

Do Not Treat a Red Eye at Home Without a Diagnosis

Many ocular issues can cause redness. Conjunctivitis, corneal ulcers, uveitis, dry eye, glaucoma, trauma, and other conditions can all produce a red or uncomfortable-looking eye. The right treatment depends on the underlying cause.

One cannot accurately assess pressure from appearance alone. Tonometry provides an objective measurement and is especially important when glaucoma is suspected. 

Cornell University College of Veterinary Medicine wrote about glaucoma in pets. Merck Veterinary Manual also wrote about pet glaucoma.

Frequently Asked Questions About Glaucoma in Pets

What are the early signs of glaucoma in a dog?

Early signs can include subtle redness, a slightly enlarged or sluggish pupil, mild cloudiness, changes in visible blood vessels, or early enlargement of the eye. Your dog may also become quieter or behave differently because elevated eye pressure can be painful. Early glaucoma is not always obvious to owners.

As pressure rises, symptoms can become much more dramatic, and vision can deteriorate rapidly. A red or cloudy eye with pain, pupil changes, or reduced vision requires prompt veterinary evaluation. 

Is glaucoma in pets an emergency?

Acute glaucoma is an ophthalmic emergency because rapidly elevated intraocular pressure can irreversibly damage the retina and optic nerve. Prompt treatment is intended to lower pressure, protect any remaining vision, and relieve discomfort. Waiting to see whether a severely abnormal eye improves can reduce treatment options.

Seek urgent veterinary care for sudden cloudiness, marked redness, a dilated abnormal pupil, obvious eye pain, or sudden vision loss. If your regular veterinary clinic is unavailable, follow its emergency recommendations. 

Can glaucoma cause permanent blindness?

Yes. Elevated intraocular pressure can damage the retina and optic nerve, and that damage can become irreversible. The amount of remaining vision depends on how high the pressure becomes, how long it remains elevated, the type of glaucoma, and how the eye responds to treatment. This is why early diagnosis is so important. Treatment cannot necessarily restore vision that has already been permanently lost, but in appropriate cases it may help preserve remaining sight. 

Comfort remains an important treatment goal even when vision cannot be saved.

Is glaucoma different in cats than in dogs?

Yes. Primary inherited glaucoma is more common in dogs, whereas cats more often have secondary glaucoma. 

Those differences can affect diagnostic testing and treatment choices. A cat with elevated pressure needs evaluation for the underlying cause, not just pressure management. Your veterinary ophthalmologist can identify the issue and recommend treatment based on the full examination.

Does glaucoma require lifelong care?

Yes. Glaucoma commonly requires long-term treatment and monitoring, because pressure can change as the disease progresses. Pets on medication need follow-up examinations to determine whether treatment is still effective. Surgical patients also require continued ophthalmic monitoring.

Dogs with primary glaucoma also need careful monitoring, as well as preventive management of the other eye. Keep scheduled rechecks even when your pet appears comfortable and sees normally. Pressure changes can develop before obvious symptoms appear at home.

Contact a Boston, MA Vet About Pet Glaucoma 

Glaucoma in dogs and cats can threaten both vision and comfort, making rapid diagnosis especially important when an eye becomes suddenly red, cloudy, painful, or visually impaired. Animal Eye Care of New England provides specialty veterinary ophthalmology for pets in the Boston, MA area, including pressure testing, glaucoma evaluation, ongoing monitoring, and treatment planning. If you are searching for an eye vet near me, a veterinary ophthalmologist, an animal eye specialist, or a veterinary clinic for suspected glaucoma, contact the clinic to schedule an appointment or seek prompt veterinary attention for sudden symptoms.

This article provides general educational information about glaucoma and is not a substitute for an individual veterinary examination or treatment plan. Always follow your veterinarian’s or veterinary ophthalmologist’s recommendations, use only medications prescribed for your pet, and seek prompt veterinary care for sudden eye pain, cloudiness, redness, pupil changes, or vision loss.

Glaucoma can threaten your pet’s comfort and vision, so specialized evaluation and ongoing management are especially important. Animal Eye Care of New England offers veterinary ophthalmology for pets across greater New England, including Boston, MA; Providence, RI; and Bridgeport, CT. Start on our Services page for an overview of available care, then explore Diagnostics, Glaucoma, Lens, Retina, and Surgery/Procedures Offered, Face/eyelids/third eyelid, for more detail.