Iris Bombe in Cats

The most common and indicative sign of iris bombe is the altered and strange appearance of your cat’s eye. The iris may appear a marbled, or different color, and the pupil may appear to have changed shape. Iris bombe can be very serious, and may cause an acute attack of angle-closure glaucoma. Glaucoma is a condition in which the optic nerve is destroyed by elevated intraocular pressure and is a cause of blindness in cats. It is very important that your cat receives veterinary treatment immediately, as it may be the difference between your cat maintaining or losing its sight.

Iris bombe is a condition that is the result of the accumulation of fluid in the posterior chamber of the cat’s eye. This fluid causes a great deal of pressure, forcing the peripheral iris to bulge. The increased fluid is the result of an irregularity of the synechia, the adhesions that attach the iris to the rest of the cat’s eyeball. This fluid-caused pressure is likely very uncomfortable and even painful for your cat and often causes mild to severe decrease in vision. 

The first symptom that will likely be noticed by pet owners is the altered appearance of the eye. In addition to this sign that your cat needs immediate veterinary attention, the following symptoms may also be present:

• Blurred, inflamed, or otherwise changed appearance of the cat’s eye
• Excessive squinting 
• Corneal lesions 
• Excessive production of tears 
• Glaucoma, seen as a clouding over of the eyes 
• Variation in lens color 
• Uveitis, which is the inflammation of the middle layer of the eyeball, and can possibly cause blindness
• Decreased reaction to light 
• Decreased sight 
• Painful Inflammation of the eye 
• Subconjunctival hemorrhage, or “bloodshot eyes”

It is not uncommon that the cause of a cat’s iris bombe is unable to be determined, even by a veterinarian. The following causes, however, may be considered by your veterinarian:

• Chronic infection 
• Side effect of surgery 
• Ocular wound(s) or injuries, often as a result of a fight with another cat or animal 
• Corneal ulcer

As is typical, your visit to the vet will likely begin with the vet listening to your report of the symptoms you have observed in your cat and to the duration of those symptoms. The vet will usually perform a thorough physical examination to determine the cat’s overall health and, if possible, review the cat’s medical history. 

• In order to diagnose iris bombe, the veterinarian, or veterinary ophthalmologist, will do a thorough ophthalmological exam on the cat, looking for the symptoms listed above.
• A tonometer may be used to measure the intraocular pressure, meaning the pressure within the eyeball.
• The vet will be looking for the signs of iris bombe as well as evidence of the glaucoma that may have developed as a result of the iris bombe.

The veterinarian will be looking for evidence that will help the vet to rule out other serious ocular conditions such as intraocular neoplasia, cataracts, persistent pupillary membranes, iris hypoplasia, and conjunctivitis.

In response to a case of iris bombe in a cat, the following two factors must be considered in devising a plan of treatment:

• Relieving the pressure produced by the extra fluid in the eye, which may allow the eye to return to its normal appearance and performance
• Addressing the possible glaucoma that may have developed as a result of the iris bombe

These two factors may be addressed in the following ways:

• The vet may choose to relieve the pressure on the cat’s eye by putting the cat on diuretics in hopes of the fluid being drawn out of the eye and passed out of the body in urine. 
• Beta blockers may be prescribed to decrease the production of fluid to relieve pressure.
• Anti-inflammatories may be prescribed to lessen swelling and irritation in the eye.
• If glaucoma has developed, the vet may choose to perform laser surgery to improve the cat’s vision.

Permanent loss of vision is always a risk with iris bombe. The likelihood of a cat retaining its sight depends upon how far the cat’s condition has progressed before treatment is sought. If the cat is seen by a veterinarian in the early stages of iris bombe while the cat’s sight is still intact, before glaucoma has developed, the cat will have a much better chance at a full recovery. There will likely be one or more follow up appointments so the vet can assess the progress of any treatments.