Glaucoma in Cats: Understanding the Silent Threat to Feline Vision

Cats are known for their keen eyesight and graceful movements. Their eyes are not only captivating but also essential for their survival. However, just like humans, cats can develop various eye conditions, including glaucoma. Glaucoma is a serious and potentially blinding eye disease that affects felines. Understanding this condition and its implications is crucial for cat owners to ensure early detection and prompt treatment, thereby safeguarding their feline companion's vision.

What is Glaucoma?

Glaucoma is a complex condition that encompasses various disorders sharing a common outcome of the optic nerve and retinal pathology, ultimately leading to vision loss. It is widely regarded as a neurodegenerative disease. Rather than being a single disease entity, "glaucomas" represent a diverse group of disorders that affect different species.

In both humans and animals, the most significant risk factor for developing glaucoma is intraocular pressure (IOP), which refers to the pressure inside the eye. 
Glaucoma is characterized by the increased pressure within the eye caused by an imbalance in the production and drainage of aqueous humor, the clear fluid that nourishes the eye. This buildup of fluid can lead to optic nerve damage, resulting in irreversible vision loss.

What is Normal IOP in Cats?

As elevated IOP leads to the progression of glaucoma, an accurate and reliable method of measuring IOP is essential for the effective diagnosis and monitoring of this disease.

The intraocular pressure (IOP) range considered normal in cats is typically between 10 and 25 mmHg (millimeters of mercury). However, it is important to note that IOP in cats can be influenced by various factors, including age. Geriatric cats generally have lower IOP than young cats, while adolescents tend to have higher IOP than adult cats. Additionally, young kittens within the first few weeks of life may have lower IOP compared to adolescent cats.

A large study involving 538 cats aged 7 years and older found that the average IOP, as measured by Tono-pen XL, was 12.3 ±4.0 mmHg. In cats that underwent multiple IOP measurements over time, there was a progressive decrease in IOP. It was not uncommon for older cats to have very low IOP levels (≤ 7 mmHg) without exhibiting any signs of anterior uveitis. This decline in IOP may be attributed to reduced active secretion of aqueous humor associated with declining systemic health.

How Do Cats Get Glaucoma?

The most direct cause is an increase in IOP, so what are the diseases that cause an increase in IOP?

Primary Glaucoma

This form of glaucoma is hereditary and often seen in certain cat breeds, such as Siamese, Burmese, and Persian. It usually affects both eyes and tends to develop gradually.

Secondary Glaucoma

Secondary Glaucoma: This form of glaucoma occurs as a result of other underlying eye conditions or factors. Some common causes include:

• Uveitis
• Lens Luxation
• Trauma
• Eye tumors
• Eye infections
• Age-Related Glaucoma

It is important to note that glaucoma can be bilateral, affecting both eyes or unilateral, affecting only one eye. Unilateral glaucoma can eventually progress to involve the other eye if left untreated.

What Does Glaucoma Look Like in Cats?

Glaucoma in cats can present with various signs and symptoms, being aware of the visual and behavioral changes associated with glaucoma can help cat owners recognize potential problems and seek veterinary care promptly. Here are some common signs that may indicate glaucoma in cats:

• Squinting or blinking excessively
• Redness or bloodshot appearance of the eyes
• Cloudiness or bluish tint in the cornea
• Dilated pupils that are unresponsive to light
• Bulging or enlarged eyes
• Increased tearing or discharge
• Reluctance to open the affected eye
• Changes in behavior, such as increased irritability or lethargy

What Are the Early Stages of Glaucoma in Cats?

During the initial phases of glaucoma, the cornea, which is the clear front surface of the eye, may exhibit subtle cloudiness or haze. This slight opacity arises from a mild accumulation of fluid caused by elevated intraocular pressure.

Moreover, one of the early signs of glaucoma in cats is the loss of peripheral or lateral vision. This means that cats may experience difficulties seeing objects or movements occurring on the sides, leading to a narrowing field of vision. Loss of peripheral vision is often the first noticeable indication of glaucoma in cats.

How is Glaucoma Diagnosed?

Your veterinarian can easily diagnose glaucoma in cats with an eye examination and an intraocular pressure or IOP (intraocular pressure) measured by an ophthalmometer.

It is important to exercise caution when diagnosing glaucoma based solely on a single elevated IOP reading. When elevated IOP is observed without clinical evidence of optic nerve and retinal damage, it is referred to as "ocular hypertension," distinguishing it from overt glaucoma.

How to Treat Glaucoma in Cats?

Important Clinical Considerations when formulating treatment strategies for feline glaucoma

Is the glaucoma primary or secondary?

1. Primary Glaucoma

The goal of treatment is to reduce intraocular pressure (IOP), alleviate discomfort, and preserve the cat's vision. 

• Medications: Medications are often the first line of treatment for primary glaucoma. The goal is to lower intraocular pressure (IOP) and prevent further damage to the optic nerve. Medications commonly prescribed include prostaglandin analogs, beta-blockers, carbonic anhydrase inhibitors, and miotics.
• Surgical Options: If medication alone is insufficient to control glaucoma, surgical interventions may be considered. Laser therapy, drainage implants, or cycloablation may be performed to lower IOP and improve fluid drainage.
• Ongoing Monitoring: Cats with primary glaucoma require regular monitoring to assess the effectiveness of treatment, IOP levels, and any changes in vision. Adjustments to medication or additional interventions may be necessary over time.

2. For Secondary Glaucoma

In cases of secondary glaucoma, addressing the underlying cause is crucial. 

Infection Treatment: Treating the underlying infection is crucial to managing secondary glaucoma. The specific treatment will depend on the type of infection, (examples include conjunctivitis, keratitis, iritis, and sclerositis) and may involve antibiotics eye drops, antiviral medications, or other appropriate therapies.

Tumor Treatment: The treatment approach for ocular tumors depends on the type, location, and size of the tumor. It may involve surgical removal, radiation therapy, cryotherapy, or other targeted therapies.

Trauma Management: Treating the trauma itself is important to address secondary glaucoma. It may involve surgical repair of any injuries, removal of foreign objects, or other appropriate interventions.

Medications: Uveitis is typically treated with anti-inflammatory medications, such as corticosteroids or non-steroidal anti-inflammatory drugs (NSAIDs). These medications help reduce inflammation in the eye and can indirectly lower IOP. Additional medication to control IOP may be prescribed if necessary.

Surgical removal:

In certain cases, surgical removal of the eye may be recommended as a treatment for feline glaucoma. This option is typically considered when irreversible blindness is present or when cancer is suspected as the underlying cause of glaucoma. While the decision to have your pet's eye removed can be distressing, it's important to remember that the eye itself can cause significant pain and discomfort.

Fortunately, cats tend to cope well with this type of surgery. With the source of discomfort eliminated, they often experience relief and adjust relatively smoothly to the loss of vision in the affected eye. Even cats who are blind in both eyes have a remarkable ability to adapt and lead fulfilling lives following the surgery.

It is normal to feel anxious or concerned about such a procedure, but rest assured that cats typically recover successfully and can continue to enjoy a good quality of life. Working closely with your veterinarian, who can provide guidance and support throughout the process, will help ensure the best outcome for your beloved feline companion.

Glaucoma in Cats FAQs

What Age Do Cats Get Glaucoma?

Glaucoma can occur in cats at any age, but it is more commonly observed in older felines. The prevalence of glaucoma tends to increase with advancing age, especially in cats over the age of seven.

Can Glaucoma in Cats Be Cured?

Unfortunately, glaucoma in cats cannot be cured. Once diagnosed, glaucoma is a chronic and progressive condition that requires ongoing management to control intraocular pressure (IOP) and preserve the cat's remaining vision.

Is Cat Glaucoma Painful?

Yes, glaucoma in cats is a painful condition. Increased intraocular pressure (IOP) in the eye causes discomfort and can lead to significant pain. The elevated pressure puts pressure on the delicate structures within the eye, including the optic nerve, which can result in damage and vision loss.

Cats are known to be stoic animals and may not always exhibit obvious signs of pain. However, there are certain indications that a cat with glaucoma may be experiencing discomfort:

• Squinting or closing the affected eye.
• Increased tearing or watery discharge from the eye.
• Redness or bloodshot appearance in the eye.
• Pawing at the eye or rubbing against objects.
• Avoiding bright light or dark environments.
• Behavioral changes, such as irritability, decreased appetite, or lethargy.

If you observe any of these signs or suspect that your cat may have glaucoma, it is crucial to seek veterinary attention promptly. Timely diagnosis and appropriate treatment can help alleviate the pain associated with glaucoma and preserve the cat's remaining vision. Your veterinarian can evaluate the cat's condition, determine the best course of treatment, and provide pain management strategies to ensure the cat's comfort.