Chorioretinitis in Dogs
Chorioretinitis is a medical condition that affects the eyes; the term refers to inflammation of the choroid and retina. The retina is a layered membrane that lines the inner eyeball and which contains the light-sensitive rods, cones, and cells that convert images into signals and send messages to the brain to allow for vision. The choroid is located immediately under the retina and is part of the middle layer of the eyeball that contains the blood vessels. The choroid is also called the posterior uvea., which is the entire middle layer of the eyeball that contains the blood vessels. The uvea is composed of the iris (the colored or pigmented part of the eye), the ciliary body (the area between the iris and the choroid), and the choroid. Spreading inflammation may result in separation of the back part of the eye (retina) from the underlying, vascular part of the eyeball (choroid); a condition known as retinal detachment. Chorioretinitis may be a sign of a generalized (systemic) disease, therefore, appropriate diagnostic testing is important.
Dogs with uveodermatologic syndrome (an immune-mediated disease that causes inflammation of the eye and loss of clear sight, along with loss of pigment in the skin and whitening of the hair) may also present as inflammation in the front part of the eye, including the iris. In the case of an uveodermatologic condition, inflammation of the skin (dermatitis) will also require management. Uveodermatologic syndrome is more likely to occur in Akitas, Chow Chows, and Siberian Huskies. An immune-mediated disease requires lifelong therapy to control inflammation of the choroid and retina.
Other causes for chorioretinitis are generalized fungal infections, known as mycoses, which are more common in large, hunting-breed dogs; and a Borzoi breed-specific eye disorder with multiple areas of fluid build-up in the retina (referred to as retinal edema) or loss of tissue in the choroid and retina (chorioretinal atrophy) resulting in deterioration of the retina, causing pigmented and hyper-reflective areas (referred to as Borzoi chorioretinopathy). Secondary glaucoma, in which the pressure within the eye is increased secondary to inflammation in the eye, can also be a complication related to inflammation, and will also require treatment.
Symptoms and Types
Chorioretinitis is not usually painful except when the front part of the eye, including the iris, is affected. Some of the symptoms that may point to chorioretinitis include vitreous abnormalities, which can display as tearing, bleeding, or will show evidence of the vitreous becoming liquefied (the vitreous is the clear, gel-like material that fills the back part of the eyeball between the lens and the retina). A condition usually seen in dogs is invasion of the eye by fly larvae. Tracts from migrating larvae may be seen when the eye is examined with an ophthalmoscope.
Changes in the appearance of the retina when examined with an ophthalmoscope may include change in color, darkened or lighter areas, scars, and changes in the contour/surface of the retina. A close examination may show few, or small, lesions.
The conditions that can lead to chorioretinitis are varied, as you can see in the list below. Your veterinarian will need to consider biological, chemical, and genetic causes, just to name a few. There is also the possibility that a cause for the condition will not be found, in which case it will be classified as idiopathic (of unknown origin) in nature.
- Fungal infections
- Bacterial infection (e.g., Rickettsia)
- Viral infections (e.g., canine distemper virus, rabies virus, and herpes virus, which is rare and usually seen in newborn puppies)
- Algal infections (water plant based infection, typically from plants growing in stagnant water)
- Protozoal infection
- Autoimmune disease
- Genetic predisposition
- Generalized infection, such as blood poisoning or bacteria in the blood
- Toxicity (e.g., antifreeze poisoning, or adverse reaction to medications)
- Physical trauma
Your veterinarian will use diagnostic tools that are both invasive and non-invasive in order to make a correct diagnosis of chorioretinitis. The non-invasive methods will include measuring your pet's blood pressure; screening a large area of the retina with indirect ophthalmoscopy (an instrument used for viewing the interior structure of the eye by use of a light reflecting mirror), or using direct ophthalmoscopy for closer examination of the affected areas of the eye. If results are not conclusive at that point, the need for invasive procedures will become a factor in pinpointing the cause for the chorioretinitis.
Your veterinarian may be able to make a diagnosis by examining a fluid specimen from the eye, which will be a fairly simple procedure, or there may be a need for a deeper examination, in which case your doctor will want to take a sample of cerebrospinal fluid (also called spinal fluid, the liquid that bathes the brain and spine) to look for infection, or for an indication of central nervous system disease or optic neuritis. Cerebrospinal fluid is removed through a procedure called a spinal tap, where a needle is inserted into the vertebrae of the spine and the fluid is allowed to collect into a vial. The sample is then sent to a lab for testing. It is a fairly quick procedure, but your pet would have to be sedated and might be affected for the rest of the day afterward.