Electroretinography (abbreviated ERG) is one of the most important tests performed in veterinary ophthalmology. It evaluates the electrical activity of the retina, meaning it checks whether the light-sensitive receptors in the form of cones and rods are functioning properly. When are there indications to perform an ERG test? What is the process like? How to prepare a dog for electroretinography?
To understand the essence of the ERG test, it is essential to clarify what the retina in the eye actually does. In simple terms – it is responsible for seeing specific images. It receives light stimuli and transforms them into an electrical impulse, which is then transmitted through the nerves to the brain. Within the retina, there are light-sensitive receptors – cones and rods – which are responsible for color and shape vision, respectively. If their function is disturbed in any way, it impacts the pet’s vision condition.
When Is an ERG Test Performed?
ERG is routinely performed before cataract surgery in dogs. This disease causes cloudiness of the lens, making it difficult to assess the condition of the retina during a standard ophthalmic examination. This is significant because any potential damage to the retina is considered a contraindication for cataract surgery.
Furthermore, ERG is one of the most effective methods for accurately diagnosing various retinal diseases, especially those in which initially there are no visible ophthalmological disorders (e.g., retinal dysplasia, day blindness, which affects German shorthaired pointers and Alaskan malamute dogs, sudden acquired retinal degeneration, etc.).
Electroretinography is also used to diagnose the initial form of progressive retinal atrophy (PRA) and dysplasia of rods and cones (rcd). These disorders most often occur in breeds such as Collie Shepherds, Norwegian Elkhounds, Cocker Spaniels, American and English Labrador Retrievers, Poodles, and Irish Setters.
How Is an ERG Test Conducted?
ERG is a completely safe and painless test for dogs. Depending on the protocol, it lasts about 10 or 45 minutes. Initially, the animal is prepared for electroretinography. The patient is placed under general anesthesia, laid on a table, and then connected to specialized equipment. Two electrodes are implanted subcutaneously, and a third one in the form of a lens is placed on the cornea. Anesthesia is administered not only to increase the dog’s comfort during the test but also to limit its movements. The animal must remain still for the results to be as reliable as possible. Before placing the lens, special eye drops are given to the dog to anesthetize the cornea and dilate the pupils.
The entire test is conducted in complete darkness. This is to eliminate the influence of daylight and enhance the response of individual retinal cells to the applied light stimuli.
What Does the ERG Test Involve?
The electrode placed on measures the electrical activity of this part of the eye. This appears as a response to a specific stimulus. The result is presented in the form of a special graph, showing the value of the received signal, which is further defined in a specific time interval. Based on this, the condition of the retina and its individual components is determined. The results of the ERG tests should be interpreted by a veterinarian trained in this field.
Right after the test, the dog is awakened. After a short while, the animal can return home with its owner.
How to Prepare a Dog for an ERG Test?
Although the ERG test is painless and safe, it is worth preparing appropriately for it. First of all, the animal should arrive at the veterinarian’s office on an empty stomach. The last meal should be given to the pet about 8-12 hours before the electroretinography. During this time, only water can be provided (especially important in summer).
It should also be remembered that after the test, the pet will likely feel somewhat unwell. It is worth providing it with special care and not overstressing it. The return to full capability after anesthesia can take the dog even a day.
This article was created in collaboration with the Veterinary Ophthalmology Center EyeVet Wrocław: https://eyevet.pl/pl