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Retinal Degeneration in Dogs

The retina is the tissue that lines the inner surface of the eye, and is the light sensitive part of the eye that acts as the brain's camera, transmitting images through the rods and cones that are part of its structure, thus enabling the experience of vision. The retina is part of the central nervous system (CNS) and the only part of the CNS that can be easily imaged and examined. In retinal degeneration, the cells of the retina begin to decline in function, thereby leading to impaired vision or even blindness. There are many causes for retinal degeneration.

Symptoms and Types

• Night blindness that progresses to blindness in light as well
• Dilated pupils
• Inability to see clearly in bright light
• In some conditions, only central vision may be lost, the animal may still retain peripheral vision
• The pupil (opening of the eye) has abnormal reactions to light
• The retinal structure appears abnormal when a doctor examines it with an ophthalmoscope; cataract may be observed
• The liver may also be affected, obesity may be observed
• Sudden blindness may be due to sudden acquired retinal degeneration syndrome (SARDS)

Dogs

• Progressive retinal atrophy (PRA) is a group of disease that worsens over time, and is seen especially in collies, Irish setters, miniature poodles, cocker spaniels, Briards and Labrador retrievers, mastiffs, X-linked in Samoyeds and Siberian huskies
• Central progressive retinal atrophy (eye disease that leads to loss of central vision, but retention of peripheral vision possibly for years) may be seen in Labrador retrievers
• Neuronal ceroid lipofuscinosis (a nervous system disorders with swelling and/or changes in some retinal cells) occurs in most breeds
• Inability to see clearly in bright light (known as hemeralopia) may occur in Alaskan malamutes
• Sudden blindness due to sudden acquired retinal degeneration or SARD is more common in middle-aged and older dogs; 70 percent are female

Mean Age and Range

• Early progressive retinal atrophy may occur three to four months of age up to two years of age
• Clinical signs of late progressive retinal atrophy are seen dogs older than four to six years of age

Causes

• Genetic
  • Hereditary degeneration is common
  • This is characterized by the formation and development of a faulty group of cells, which gradually worsen in function over life
• Degenerative
  • Long-term glaucoma, scarring inflammation or separation of the retina due to trauma
• Abnormal structure
  • Abnormal structure at birth or abnormal development of the retina with age
• Metabolic
  • Insufficient or excess amounts of certain enzymes
• Cancer
  • Cancer from other parts of the body that has spread to the retina
• Nutritional
  • Deficiency of Vitamin A or E
• Infectious/Immune
  • Infections of the retina or infections that spread from other parts of the body
• Idiopathic (Unknown Cause)
  • Sudden blindness due to sudden acquired retinal degeneration syndrome (SARDS)
• Toxic
  • Adverse Reactions to specific drugs

Diagnosis

You will need to give a thorough history of your dog's health, onset of symptoms, and possible incidents that might have led to this condition, such as trauma or exposure to toxic substances. Your dog's diet will also be taken into consideration, since this may be a supporting cause.

Your veterinarian will perform a complete physical exam on your dog, taking into consideration your dog's lineage and whether there might be a genetic link. Standard laboratory tests include a blood chemical profile, a complete blood count, an electrolyte panel and a urinalysis, in order to rule out other causes of disease.

The physical exam will entail a full ophthalmic exam using a slit lamp microscope. During this exam, the retina at the back of the eye will be closely observed for abnormalities and the electrical activity of the retina will also be measured.

Genetic testing may also be done if your dog belongs to a breed that is prone to familial retinal disease. Additionally, hormonal causes may bring about retinal disease, and this will be considered as well. X-rays, computed tomography (CT) and magnetic resonance imaging (MRI) can be used effectively to screen for the effects of hormonal abnormalities.