Cat Glaucoma Explained

Glaucoma is a disease of the eyes which affects the optic nerve, located at the back of the eye. In a cat with glaucoma, the optic nerve will slowly be destroyed and the eventual loss of vision will occur. Glaucoma can be divided into two categories: primary and secondary. Because glaucoma is one of the most common causes of blindness in cats, pet owners should be aware of the different types, the causes, how it can affect their cat, and how it can be treated.

What Causes Glaucoma?

Glaucoma is caused when pressure builds up in the eye. Under normal conditions, the eye produces a watery fluid known as aqueous humor. That liquid is responsible for maintaining the structure and shape of the eye. Normal pressure is maintained in the eye by the constant production and drainage of the fluid. However, when that fluid is not able to drain properly, an increased amount of pressure starts to build. The pressure, in turn, causes the structures of the eye to become damaged. When the optic nerve is damaged, the eventual loss of sight is imminent.

Primary Glaucoma

Primary glaucoma is a condition which tends to be inherited. Although, this particular type of glaucoma is  uncommon in cats, it is not unheard of. Primary glaucoma usually starts out only affecting one of the eyes. However, it can lead to destruction of the other eye shortly after it presents itself.

Secondary Glaucoma

Secondary glaucoma is considered to be a side effect of a separate eye condition. There are a few situations which can lead to the presentation of secondary glaucoma. They include:

  • Uveitis - A severe inflammation which causes debris to float in the watery fluid of the eye (aqueous humor). This debris can interfere with the normal drainage of the liquid and cause the iris to become inflamed. This is the most common cause of glaucoma in cats.
  • Cataracts - A cloudy appearance over the lens of the eye.
  • Cancer or Tumor - Both cancers and tumors of the eye can block normal drainage.
  • Trauma - Severe trauma to the eye can cause it to fill with blood and block the normal pathway of drainage.

Signs of Glaucoma

The first sign to usually present itself is complete blindness. However, there are some other signs to watch for. They include:

  • Red eyes
  • Inflammation of the eyes
  • Constant squinty and painful appearance
  • Tearing
  • Dilated pupils that don't respond to light
  • Cloudy and glassy surface over the eye
  • Enlargement of the eye

How Does Glaucoma Affect Your Cat?

Regardless of whether the condition develops over time or a sudden onset of pressure develops, the condition is quite painful. Because the fluid is not draining properly, there is no release for the pressure. That amounts to a very painful situation for your cat. The cat's reaction to this may be to paw at the area or rub their head on the floor in an attempt to alleviate the pain. It is also very likely that their eyes will be sensitive to bright light. In an emergency situation, pressure can rise instantly and cause an explosive feeling in the eye. At that point, vision will be lost within minutes.

How Is Glaucoma Diagnosed?

There are two devices used to diagnose glaucoma:

  • Tonometer - Measures the pressure in the eye and determines if glaucoma is present.
  • Gonioscopy - Determine which type of glaucoma is present. This method will also determine how much of the remaining vision is likely to be compromised.

Neither of these testing procedures is painful for you cat. A general anesthetic is given in the eye to deaden it, and then the procedure if performed.

Treatment of Glaucoma

The purpose behind treatment is to relieve the pressure in the eye, reduce the amount of fluid that it produces, increase the fluid drainage, and to provide pain relief. The following medical treatments may be given to your cat:

  • Diamox - Used to decrease fluid pressure
  • Pilocarpine - Used to relieve pain and encourage fluid drainage

The use of these medications cannot reverse glaucoma. However, they can provide temporary relief to your cat. 

Surgery would be the next viable option. Surgery is usually performed to save any remaining portion of the eye that can be saved and provide pain relief. The most commonly used surgical procedure is the destruction of the cells in front of the eye that produce the fluid. When vision cannot be saved, the ultimate goal of surgery is to provide pain relief and save the eye. However, if there is no likelihood of saving vision, removing the eye can prevent future problems from arising.