Optic Nerve Swelling in Cats

Inflammation may be confined to only the optic nerve or it may involve the optic head (papillitis). It can also damage the space behind the eye, resulting in retrobulbar neuritis. The disease leads to the loss of nerve conduction causing either partial or complete blindness, which is often sudden in onset. Early intervention may prevent permanent blindness. It is a very rare condition in cats.

Optic neuritis refers to a disease that interferes with optic nerve function whether inflammation is present or not, though it usually is. The optic nerve transmits signals and images from the retina to the brain so that it may interpret what the eye is perceiving. Optic neuritis can affect either one or both eyes and is usually due to a secondary condition or an underlying disease such as that affecting the central nervous system or a systemic infection, although occasionally the source is unknown (idiopathic). Accompanying deterioration of the myelin sheath surrounding the nerve disrupts or completely blocks the nerve’s communication with the brain. 

Symptoms of optic nerve swelling commonly include:

• Fixed and dilated pupils
• Inability to see clearly
• Pain when moving the eye
• Headache
• Extreme disorientation
• Sudden bumping into objects 
• Distress
• Swollen optic nerve head
• Diminished pupillary reflex to light

Types

• Papillitis: Also called intraocular optic neuritis, a specific type of optic neuritis in which the optic nerve head is inflamed. Edema may or may not accompany the inflammation. 
• Retrobulbar optic neuritis: Inflammation of the optic nerve behind the eyeball, but with a normal-appearing optic nerve head. 

Inflammation of the optic nerve rarely occurs on its own unless it is in conjunction with a systemic condition. However, in some cases, its origin is unknown (idiopathic) and seems to occur spontaneously.

• Inflammatory disease of the brain
• Viral infection such as feline infectious peritonitis (FIP)
• Systemic fungal or bacterial infection
• Inflammatory disease of the surrounding tissues of the eye
• Trauma
• Lead poisoning
• Toxoplasmosis (parasites)
• Vitamin A deficiency 
• Cancer of the eye
• Retinal degeneration
• Hypertension

The veterinarian will begin with a simple physical examination including a careful examination of the eye with an ophthalmoscope, which will identify any presence of inflammation. If inflammation is found, other in-office tests will be performed.

A blood test, CBC, and urinalysis will help to detect any underlying infectious diseases, and your cat’s blood pressure will be taken to determine hypertension. If these tests show a positive result indicating optic neuritis, your veterinarian may refer you to a board-certified veterinary neurologist for additional testing.

A neurologist will conduct an electroretinogram (ERG) to determine the functionality of the retina. This procedure involves sedation in order to get a clear view of the inner eye. A fluorescein dye will be injected into the bloodstream to highlight the retina and choroid at the back of the eye, which helps the neurologist to determine the rate of blood flow through the eye.

While under sedation, the neurologist may conduct an MRI or CT scan to check for any signs of disease within the brain, and a sample of the cerebrospinal fluid surrounding the brain will be taken. This fluid aids in maintaining the health of the central nervous system. Any abnormalities would indicate an underlying condition and would require further testing unrelated to optic neuritis.

Treatment is largely dependent upon the primary cause of the inflammation. Your veterinarian will discuss with you the necessary steps to address the underlying cause of the optic neuritis.

In all cases, topical and systemic corticosteroids (prednisone) are administered to help reduce the swelling around the optic nerve. NSAIDs may also be prescribed to help reduce swelling. These medications may temporarily increase thirst, urination, and appetite. 

Pain medication may be given as well as a course of antibiotics if an infection is apparent. If your cat is found to be hypertensive, medication to control blood pressure may also be prescribed.

Your veterinarian will want to continue monitoring your cat’s gastrointestinal, liver, and kidney functions and its blood pressure during the course of treatment for signs of adverse change.

If the cause of optic neuritis is idiopathic (of unknown origin), your veterinarian will still prescribe certain medications to help control your cat’s symptoms and provide comfort as your cat makes the adjustment to vision loss.

Early and quick intervention in the underlying condition causing optic nerve inflammation will increase the chances of your cat’s vision being completely restored. Often a return of the pupillary reflexes and normal pupil size returns within several days of treatment, with normal vision returning a few days after that.

However, in some cases, partial or complete blindness is still possible if the inflammation has persisted long enough to destroy the fibers the nerve uses to communicate with the brain due to the inability of the fibers to heal and repair itself.

Whether vision is restored or not, you will need to schedule regular check-ups with your veterinarian to make sure that your cat’s eye health is maintained.

If blindness is permanent, be assured that cats usually adjust to it rather well, especially if the blindness was slow in onset. Their other senses take over to help them find their way around. If the blindness was quick in onset, though, you may see some initial distress in your cat. Signs of withdrawal are common and he or she may stay near the places they are very familiar with and know to be safe. 

As your cat makes the adjustment to its loss of sight, be sure not to make any changes in your home right away. Keep furniture and other objects in their usual places, and make food and water bowls and litter boxes easily accessible. Approach your cat quietly and carefully so as not to scare him since he can’t see you coming. Your cat may still go outside if it is in an enclosed area and one you can easily monitor.

With time, love, and careful attention to unchanging surroundings, most cats adjust well to blindness and go on to live a normal, happy life.