The retina is a highly complicated tissue located in the back of the eye. Light strikes the retina and starts a series of chemical reactions that causes an electrical event (nerve impulse). The impulse passes through the layers of the retina to the optic nerve and from there to the brain where vision takes place. In the retina, cells called rods are involved with black and white or night vision, and cells called cones are involved with colour or day vision.
WHAT IS SARD? SARD is a condition characterized by a rapid onset of blindness. This condition may strike any breed of dog. Pets who develop SARD are often older than 6 years of age. Examination of tissue specimens from some patients at research institutions has indicated that the retina in these pets is totally destroyed and cannot regenerate. Blindness occurs very quickly over a few weeks, or in some cases – over a few days. A typical pet may have gone out on a walk with the owner one day and been normal, but the next day be bumping into everything in the house.
HOW IS SARD DIAGNOSED? The ophthalmologist will examine the retina with an instrument called an indirect ophthalmoscope. A test known as an electroretinogram (ERG) is essential for accurate diagnosis. This test involves sophisticated instrumentation used to measure the response of the retina when a light is shone upon it. Your pet will need to be anesthetized and placed in a dark room. This may require a separate appointment. A special contact lens connected to a computer is placed on the eye and two tiny needles are placed under the skin. A light source is flashed periodically into the eye and the computer evaluates the response. Blood tests will also need to be run to rule out any systemic disease that may cause blindness. Non systemic conditions that can mimic SARD are brain tumors and optic neuritis (nerve inflammation). Diagnosis is important because systemic disease and optic neuritis can be treated with medication and vision may be restored.
WHAT IS THE TREATMENT FOR SARD? Unfortunately, there is no cure for SARD. Although we do not completely know the cause of and cannot treat SARD, you should know that this is not a painful condition, but you and your pet will need to adjust and deal with the blindness.