Synechiae in Dogs

The iris is the colored part of the eye that controls the amount of light reaching the lens. It contracts to make the pupil larger or smaller depending on the amount of light present. The iris sits between the cornea in front and the lens cover behind. Various eye problems may cause the iris to be displaced and stick to either the cornea or the lens cover. This condition is known as synechiae. It often occurs in combination with an infection of the uvea or middle part of the eye, or as a complication of surgery or injury to the eye. The condition is a concern since it is often a precursor to the development of secondary, non-hereditary glaucoma and it can make operation on cataracts more difficult. 

The iris can sometimes become displaced and adhere to another part of the eye, usually as the result of an eye infection or injury. Veterinarians call this condition synechiae. In dogs, it can often lead to the development of more serious eye problems.

Synechiae occurs most commonly as a result of an eye infection, so it is often recognized by symptoms of infection. This condition needs immediate treatment. You should see a veterinarian as soon as possible if you notice any of the following symptoms in your dog:

• Eye pain
• Red eyes
• Squinting
• Avoidance of bright light
• Cloudy eyes
• Bleeding or evidence of tearing in the eye

Types

Synechiae is defined by whether the iris sticks to the part of the eye in front of it, or behind.

• Anterior synechiae - the iris is stuck to the cornea
• Posterior synechiae - the iris is stuck to lens cover
• 360⁰ Posterior synechiae or iris bombe - severe form of posterior synechiae where the iris bulges forward

Synechiae commonly forms as part of an infection.

• Uveitis - infection of the uvea, or middle part of the eye. The uvea is made up of the iris, ciliary body, and choroid. Infection may include only the iris and ciliary body (anterior uveitis) or all three (posterior uveitis.) It may be due to a bacterial infection, a metabolic imbalance, an auto-immune response or even cancerous tumors. Repeat episodes present the most problems and have a higher chance of creating synechiae.

Other possible causes included:

• Trauma or injury to the eye
• Cysts on the iris - more common in Golden Retrievers and Great Danes.
• Corneal ulcer
• Corneal laceration
• Complications after eye surgery
• Diabetes

The veterinarian will perform a complete eye exam. Extreme synechiae may be visible to the naked eye, but even mild forms will be visible with a magnifying glass or ophthalmoscope. The veterinarian will also measure the pressure in your dog’s eye using a tonometer, dilate the pupils and check for reactions to light and other signs of poor vision. Your dog may be referred to an eye specialist depending on the extent of your veterinarian’s practice. 

As well as diagnosing synechiae, the veterinarian will attempt to determine the condition which caused it. Synechiae can develop as a complication of eye surgery, so if your dog has just been treated for another eye condition that will be an obvious answer.

It is sometimes difficult to find the cause for repeat eye infections. Uveitis can be related to a variety of problems, from bacteria, to autoimmune responses, to cancer, so the veterinarian may run additional tests to determine the cause of the original uveitis. This will likely include a complete physical examination including blood and urine tests, and probably X-rays or ultrasound as well.

The veterinarian will treat any immediate infection with antibiotics and pain medication. There isn’t a specific treatment for synechiae, although sometimes medication which dilates the pupils can alleviate mild forms or prevent it from developing. If the pupils can dilate normally, this suggests that the synechiae isn’t a serious problem.

If uveitis was the cause, treatment will likely include an attempt to avoid a repeat infection. Mild uveitis doesn’t usually cause a problem, but repeated episodes are what lead to the development of more problematic synechiae which can create further vision complications. Anti-inflammatory drugs are often prescribed to prevent recurring uvea infections, especially where the cause is undetermined.

If your dog has been diagnosed with synechiae, he should have regular eye exams and be monitored for the development of glaucoma. Posterior synechiae following uveitis is one to the primary precursors to the secondary, non-hereditary form of glaucoma. Diabetes is also a common cause of eye problems which can lead to synechiae, so if you know your dog has diabetes he should have his eyes monitored regularly. In the event the synechiae leads to vision loss, you may need to modify your dog’s lifestyle to accommodate near sightedness or complete blindness. Your dog will likely still lead a fulfilling life with this condition, but he will need monitoring and regular medical appointments.