Sudden Acquired Retinal Degeneration Syndrome (SARDS) causes rapid and irreversible blindness in dogs. It develops when the photoreceptor cells in the retina, which convert light into signals for the brain, abruptly stop working. The sudden vision loss, combined with other systemic signs, creates a confusing clinical picture that can lead to misdiagnosis. Understanding why these errors happen helps ensure dogs receive a timely and correct diagnosis.
Recognizing SARDS Symptoms
The most apparent sign of SARDS is a sudden and complete loss of vision, occurring over just a few days to weeks. Owners may notice their dog bumping into furniture, getting lost in familiar spaces, or hesitating to navigate stairs. The dog’s pupils may also appear constantly dilated, even in bright light.
Beyond the blindness, many dogs with SARDS exhibit systemic symptoms that can appear weeks before vision loss is apparent. These include increased thirst (polydipsia), more frequent urination (polyuria), and a greater appetite (polyphagia), which often leads to weight gain. These signs are not secondary to the blindness but are part of the syndrome itself.
Why SARDS is Often Misdiagnosed
The primary reason SARDS is frequently misdiagnosed is the strong overlap of its systemic symptoms with more common diseases. The increased thirst, urination, and appetite are also hallmark signs of endocrine disorders like Cushing’s disease or diabetes mellitus, steering the initial investigation away from the eyes.
Another challenge is that in the early stages of SARDS, the retina itself appears normal during a standard ophthalmic examination. The photoreceptor cells cease to function before they physically degenerate, so there are no immediate structural changes to observe. This lack of visible evidence can be misleading when systemic signs are prominent.
SARDS is also less common than the diseases it mimics. For a general practitioner seeing a dog with increased thirst and appetite, Cushing’s disease is a more frequent diagnosis. Consequently, blood tests for hormonal issues are often performed first, and SARDS may only be considered after these tests fail to provide a clear answer.
Common Misdiagnoses for SARDS
SARDS is most commonly mistaken for Cushing’s disease (hyperadrenocorticism). The hallmark signs of Cushing’s—excessive thirst, urination, hunger, and weight gain—are nearly identical to the systemic signs in most SARDS cases. This can lead to extensive and costly hormonal testing before SARDS is considered.
Diabetes mellitus is another condition that shares the symptoms of increased thirst and urination. While diabetes can lead to blindness from cataracts, the vision loss is more gradual. The mechanism is also entirely different from the sudden retinal death seen in SARDS.
Other causes of sudden blindness can also complicate the diagnosis. Optic neuritis (inflammation of the optic nerve) and central nervous system disorders like a brain tumor can cause acute vision loss. Progressive Retinal Atrophy (PRA) causes gradual blindness, but owners might only notice it in its final stages, perceiving it as a sudden event. These conditions can be confused with SARDS if a full retinal evaluation is not performed.
Achieving an Accurate SARDS Diagnosis
Confirming a SARDS diagnosis begins with a detailed patient history. Pet owners should document the timeline of vision loss and the onset of other signs like increased drinking or appetite. Communicating the rapid progression of blindness is important, as it helps differentiate SARDS from more gradual conditions.
A thorough ophthalmic examination is the next step, but the retina may appear normal. Pupillary light reflexes (PLRs) can be sluggish or diminished, but are sometimes present in the early stages. This is why specialized testing is necessary for a definitive conclusion.
The gold standard for diagnosing SARDS is an electroretinogram (ERG). This test, performed by a veterinary ophthalmologist, measures the electrical response of retinal cells to light. In a dog with SARDS, the photoreceptors are non-functional and produce a “flatline” ERG, confirming the diagnosis even when the eye looks normal. Blood tests are also performed to rule out mimicking conditions.
Steps if You Suspect Misdiagnosis
Pet owners should trust their observations, particularly regarding the sudden and complete nature of their dog’s vision loss. If a dog was diagnosed with another condition like Cushing’s disease but treatment is not helping and the blindness persists, it may be time to reconsider. The acute loss of sight is the distinguishing sign that sets SARDS apart.
Seeking a second opinion from a board-certified veterinary ophthalmologist is a proactive step. These specialists have the equipment and experience to perform and interpret an ERG to confirm SARDS. Before the appointment, owners should gather all previous medical records and exam notes to provide a complete history.
While there is no cure for the blindness from SARDS, an accurate diagnosis is beneficial. It prevents unnecessary and expensive treatments for the wrong disease. It also provides owners with a clear understanding of their dog’s condition, allowing them to focus on supportive care and adaptations for life without sight.