What is Glaucoma?
Glaucoma is a complex eye disease that causes damage to the retina and optic nerve, often leading to vision loss. In cats, its key feature is elevated intraocular pressure (IOP).
The eye constantly produces a fluid called aqueous humor, which normally drains out to maintain healthy eye pressure. However, if the drainage becomes blocked, fluid builds up inside the eye, causing pressure to rise above the normal level (<30mmHg in cats). This increased pressure damages the retina and reduces blood flow to the optic nerve, leading to progressive blindness if left untreated.
In addition to vision loss, glaucoma is often painful. Humans with the condition describe it as similar to a constant migraine, making early diagnosis and treatment essential for preserving both vision and comfort.
What causes Glaucoma?
Glaucoma in cats can develop due to various causes, but it is generally classified into two main types:
Primary Glaucoma – Caused by a faulty drainage system in the eye. Certain breeds, including Burmese, European Shorthair, and Siamese cats, are genetically predisposed to developing this condition.
Secondary Glaucoma – Caused by other eye conditions that interfere with fluid drainage, leading to increased pressure.
Common causes include:
- Uveitis (intraocular inflammation)
- Lens dislocation
- Intraocular bleeding
- Intraocular tumors
Identifying the underlying cause is essential for determining the best treatment approach and preserving vision whenever possible.
How is glaucoma diagnosed?
Glaucoma is diagnosed based on clinical signs and intraocular pressure (IOP) measurement using a tonometer.
Signs may include:
- Eye enlargement
- Redness (scleral vascular engorgement)
- Squinting and increased tearing
- Cloudy or “glassy” cornea
- Pupil dilation
- Vision disturbances
Determining the Type of Glaucoma
It is essential to determine whether the glaucoma is primary (genetic) or secondary (caused by another eye condition).
Our ophthalmologists will perform a complete eye examination to assess:
- How long the eye pressure has been elevated
- The extent of vision loss
- The underlying cause of the increased pressure
Advanced Diagnostic Tests
- Gonioscopy – This test evaluates the fluid drainage pathway of the eye to determine if glaucoma is primary or secondary.
- Ultrasound Biomicroscopy (UBM) – If further information is needed, this detailed imaging test provides a full view of the drainage system. Since precision is required, your cat will need to be sedated for the procedure.
Early and accurate diagnosis is crucial for preserving vision and preventing pain.
How Is Glaucoma Treated?
Glaucoma is typically first managed with medicated eye drops to help control intraocular pressure (IOP).
These drops work by either:
- Reducing the production of fluid inside the eye
- Enhancing fluid drainage to lower pressure
Some cases may require a combination of both approaches. However, glaucoma is ultimately considered a surgical disease, meaning that long-term pressure control and vision preservation are often best achieved through surgical intervention.
Monitoring Treatment Response
To assess how well your cat is responding to treatment, your ophthalmologist may recommend an intraocular pressure curve. This involves measuring IOP multiple times throughout the day, as a single reading only provides a limited snapshot of pressure fluctuations. This helps determine whether further intervention is needed.
Surgical Treatment Options
If medication alone is not sufficient, surgery may be the only way to control pressure and prevent pain.
There are two main surgical approaches:
- Increasing Fluid Outflow – A shunt (drainage device) is implanted to help excess fluid exit the eye more effectively. There are various types of shunts, and they may be used alone or in combination with other techniques.
- Reducing Fluid Production – Techniques are used to selectively destroy fluid-producing cells, decreasing pressure.
What Are the Success Rates of Glaucoma Surgery in Cats?
Currently, there are no published studies evaluating the success of glaucoma surgeries in feline patients. However, based on our experience, the outcomes in cats appear to be similar to those in dogs.