PRESENTING SIGNS

Dogs are normally presented with a sudden onset painful eye, often with colour change, and sometimes with reduced vision. The pain is manifested by the patient holding the affected eye closed with increased lacrimation and photophobia. The dog might shy away from attention to this side of its face, or may be seen rubbing the eye. Owners will often also comment that the dog is depressed. The condition can be either unilateral or bilateral. Any age of dog can be affected and there is no particular breed predisposition which is a reflection of the wide variety of causes for uveitis in dogs.

CASE HISTORY

Since there are so many potential causes for uveitis the history can be variable. A few common examples are the dog returning from a walk with a sore eye, which might suggest a traumatic uveitis (due to blunt or penetrating injury). A recently vaccinated puppy might present with a ‘blue’ eye – which despite being a vaccine reaction to the canine adenovirus 1 vaccine is surprisingly often unilateral not bilateral. Thankfully this condition is not commonly encountered with modern vaccines. A history of recent travel abroad, especially to the Mediterranean, might alert one to possible Leishmania infection. The patient might have suffered from mammary carcinoma a few months previously which could be relevant to the ocular symptoms. Thus it is very important in all cases of uveitis to take a detailed history. This can point us in the right direction regarding further diagnostic tests and will help to rule out certain causes of uveitis immediately.

CLINICAL EXAMINATION

General clinical examination can be normal but may show abnormalities. For bilateral cases of uveitis an underlying systemic problem is possible and should be considered. Such patients might be pyrexic, have a lymphadenopathy, foci of pain or an abdominal mass. Unilateral cases might be traumatic, and careful evaluation for evidence of injury (e.g. bite wounds around the face, severe bruising, etc.) might be noted.

The typical ophthalmic signs of uveitis are episcleral congestion with conjunctival hyperaemia, corneal oedema, miosis and increased lacrimation (see Table 33.1). Pain is normally present such that the examination might be resented. The ocular discharge is usually serous. Vision might be reduced, especially if there is posterior segment involvement. Aqueous flare is often present, sometimes along with frank hypopyon or hyphaema. The iris will be dull and swollen, with rubeosis iridis, although this is quite difficult to appreciate in dogs with dark irides as most do have; however, it is readily noted in blue-eyed dogs. Redness might also be present around the limbus encroaching on the cornea – ciliary flush – or inflammation of the deep episcleral vessels with growth into the cornea (Figure 33.1).

Table 33.1 Ophthalmic signs of canine uveitis

Figure 33.1 Acute anterior uveitis in a Shih Tsu. The pupil has been dilated with atropine but note the episcleral congestion, corneal oedema, out-of-focus appearance to the iris due to aqueous flare and faint fluorescein uptake (ventrally). The dense white spot at 12 o’clock close to the limbus was the site of a traumatic perforation which caused the inflammation. Intraocular pressure was 8 mmHg.

Fluorescein testing should be performed. Usually this will be negative, unless a traumatic incident has occurred or the patient has traumatized the eye secondarily. Measurement of intraocular pressure (IOP) is important and normally readings will be low – commonly 6–10 mmHg. Evaluation of the posterior segment might not be possible. Indirect ophthalmoscopy is likely to be more rewarding than using a direct ophthalmoscope. Mydriasis will assist with fundus examination, but many cases of uveitis will be slow to dilate with tropicamide such that several drops need to be applied over 30–40 minutes before adequate dilation is achieved. Vitreal haze (hyalitis) might be noted along with retinal detachment or areas of active chorioretinitis. These will be seen as dull grey areas within the fundus. Perivascular oedema might be noted as a result of leaky blood vessels. The optic disc is usually normal on examination.

CASE WORK-UP

If the cause for the uveitis is identified on clinical examination – a deep corneal ulcer or head trauma for example – then specific work-up for the uveitis is not always required. Unfortunately, the inciting agent is elusive in most cases and extensive investigation can be required to identify the underlying cause. If the cornea or anterior segment is too opaque to allow direct visualization, then ocular ultrasonography should be considered. In unilateral cases this could well outline a uveal tumour for example, or perhaps demonstrate a posterior scleral rupture following blunt trauma.

It is the bilateral cases that can be the most challenging to diagnose. Clearly a systemic problem is likely and routine blood screening with haematology and biochemistry profiles are a minimal baseline. These might highlight an infectious aetiology such that more specific diagnostic tests are indicated or suggest a blood dyscrasia or neoplastic process. Generalized septicaemia such as associated with pyometra can cause uveitis. Therefore, the basic screen might suggest that clotting profiles are indicated, or perhaps Toxoplasma, Ehrlichia, Leishmania or Borrelia titres. Mycotic causes for uveitis are rare in the UK but should be considered in immunocompromised patients or those that have travelled through endemic areas. Migrating parasite larvae, such as Toxocara canis, Angiostrongylus vasorum and, less commonly, Dirofilaria immitis, can all trigger an acute uveitis. Faecal examination can be diagnostic in such cases. Some possible causes of uveitis are listed in Table 33.2.

Table 33.2 Possible causes of uveitis

If the uveitis is severe but no cause can be identified, then referral for aqueocentesis or vitreocentesis can be considered while the eye(s) is/are still potentially sighted. By the time a secondary glaucoma has developed the prognosis for saving vision is very poor, and enucleation can be considered both on humane grounds but also as a diagnostic aid. Clearly this is a last resort!

Abdominal ultrasonography is sometimes useful as part of the uveitis work-up – especially if neoplasia is suspected. Most cases of bilateral uveitis which are associated with neoplasia are secondary – lymphoma, myeloma or mammary carcinoma for example.

If all diagnostic tests are negative, then one assumes a diagnosis of idiopathic or immune-mediated uveitis. Symptomatic treatment is started, but further tests might be warranted if the patient does not respond as expected or develops other clinical signs.

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