SUDDEN VISION LOSS

Sudden vision loss in dogs can be due to problems in one of three areas: the retina, the optic nerve or in the brain.

Possible causes include

Retinal causes:

1. SARDs - sudden acquired retinal degeneration syndrome

• Vision loss may occur over a few days to several weeks.
• This may occur in dogs of all ages.
• Some dogs may have a history of increased thirst, urination and/or appetite and may have gained weight. Some dogs with SARDs also have Cushing’s Disease, a hormonal disease whereby the adrenal produces too much cortisol. Blood tests with your local veterinarian will help to diagnose this condition or rule it out.
• The retina is normal on examination early in the disease, but may show signs of degeneration months after the vision loss has occurred.
• The cause of SARDs is unknown and there is no treatment
• Cases of SARDs usually have a reduced PLR (pupillary light response).
• SARDs can be confirmed by ERG (electroretinogram) which is flat showing no retinal activity.

2. Retinal Inflammation and Retinal Detachments.

• On examination of the retina, inflammation is seen as subtle to marked changes in many cases whilst in others the retina appears normal. Retinal detachments are usually clearly visible.
• The cause of this condition is unknown, however is suspected to be immune-mediated.
• Treatment of this condition involves the use of oral cortisone tablets.
• Over 50% of cases respond to cortisone.
• Inflammation may recur.

Optic Nerve causes:

1. Optic Neuritis = inflammation of the optic nerve

• Vision loss in these cases is usually very sudden and in many cases both eyes are affected.
• This condition may affect any breed, but appears to be more common in Maltese.
• The pupils are usually very dilated and not responsive to light.
• On examination of the optic nerve, signs of inflammation may or may not be seen depending on what part of the nerve is affected (into the eye versus behind the eye).
• The cause is suspected to be immune-mediated inflammation, however some cases may be related to an inflammatory condition of the brain called GME = Granulomatous Meningoencephalitis.
• ERG (electroretinogram) is normal in cases of optic neuritis.
• Treatment is oral cortisone tablets.
• Approximately 50% of cases respond and some vision is regained. This may only be in one eye, suggesting that the inflammation was present in one eye first.
• If there is no improvement with cortisone, further tests can be performed including imaging of the brain (CT scan or MRI).

2. Tumour at the optic chiasm

• Occasionally tumours can grow in a position that affects the crossover point of the optic nerves.
• Such tumour may extend from the nasal cavity or surrounding structures and compress the optic nerves. In such cases other signs may be seen (eg nasal discharge or sneezing).
• The pupils are usually dilated and non-responsive, and ERG is normal.
• Diagnosis of this condition is by skull and brain imaging techniques (Xrays and scans).

Central (Brain) causes

Causes of central blindness include:

Diagnosis of such conditions is via brain imaging techniques (CT or MRI) Liver shunts are most common in younger animals and affected animals usually show other neurological signs. Diagnosis of this condition is via blood tests etc.

ERG – Electroretinography

ERG is very beneficial in differentiating different causes of sudden vision loss. This can be important with respect to possible cortisone therapy, as this may be contraindicated in some animals.