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Uveal cysts: treat or not treat?

Author : CHRISTINE HEINRICH

Categories : Vets

Date : January 12, 2015

CHRISTINE HEINRICH DVOphthal, DipECVO, MRCVS

IT’S Monday and your first client is a distressed Mr Hunt. Over the weekend he has noted what he believes to be a pigmented tumour in the left eye of his four-year-old working trial Labrador retriever, Grouse (Figure 1).

The generally steadfast gun dog trainer is shaken by the thought of his future champion dog losing sight so crucial to competing at high level – not to mention even potentially losing an eye to cancer.

Fortunately, you have an interest in eyes and quickly ascertain the darkly pigmented sphere in the ventral anterior chamber of Grouse’s eye is an iris cyst rather than an iris melanoma. To assure Mr Hunt of your diagnosis, you use a Finoff transilluminator (Figure 2) to demonstrate the lesion has the typical characteristics of a cyst as compared to a tumour by being a perfect sphere – and by being translucent when transilluminated. What’s more, you are able to show Mr Hunt a smaller cyst is also already present in the fellow eye (Figure 3).

Question

Mr Hunt is relieved to know Grouse does not have an intraocular tumour, but he is worried. What impact might the pigmented uveal cysts have on his dog’s vision and performance in competitions? Should treatment to remove them be considered?

Answer

1 / 9 Single uveal cysts are a benign and often incidental finding in dogs, but some patients may also present with multiple cysts in both eyes. Most uveal cysts generally occur without any precedent or concurrent ocular disease and originate from the pigmented epithelium of the iris or ciliary body. Theories exist suggesting the cysts are present at birth, but do not start to grow and slowly detach to become free-floating until later in life. As the cysts grow, they may become “wedged” in the visual axis and sometimes cysts collapse spontaneously, leaving pigmented deposits on the central to ventral corneal endothelium.

There is no absolute answer to whether uveal cysts require treatment. In many dogs, single or multiple cysts may be present, floating in the anterior chamber, intermittently impairing the visual axis without any obvious effect on the dog’s visual behaviour. However, in other cases, “fly snapping” has been observed and in dogs with multiple cysts, clients report their dog misses objects during play or collides with small branches and obstacles in the environment.

Removal of iris cysts is possible non-invasively by laser ablation or surgically by aspiration with a needle or by irrigation and aspiration with custom-made hand-pieces. All three methods carry potential risks, require sedation (laser treatment) or general anaesthesia and firmly belong in the hands of a veterinary ophthalmologist.

It is therefore often suggested to leave small and free-floating cysts alone and only plan to intervene with removal once a cyst grows to a size where it impairs the pupillary axis, or when it becomes “stuck” between lens and cornea. However, at this point the cyst wall is likely to attach permanently to the corneal endothelium, causing opacification of the visual axis (Figure 4a and 4b) and potential later focal corneal oedema and corneal ulceration due to endothelial dysfunction (Figure 5). Attempts to remove an iris cyst at this stage are likely to be incomplete with all three methods and focal permanent endothelial pigmentation or opacification will remain. Removal is therefore carried out more safely and successfully while it is small and free-floating. Ideally, referral for a specialist assessment and discussion of pros and cons of intervention in each case is recommended early – as soon as the cysts are diagnosed and before they become stuck.

Take home message

While most uveal cysts are benign and incidental findings, their removal should be considered early on to prevent development of corneal complications and visual impairment, which will occur in some patients. Cyst removal should specifically be considered in working and service dogs. However, given many dogs live apparently undisturbed by their cysts, some owners may elect not to proceed with treatment after being given a chance to review all their options.

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Figure 1. A heavily pigmented uveal cyst in the ventral anterior chamber of Grouse’s left eye. Note the cyst’s perfect spherical shape, distinguishing it from an iris melanoma. To transilluminate the cyst, a very bright light source should be shone at it from one side while the lesion is observed from the other.

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Figure 2. Use of a Finoff transilluminator to show translucency of even a heavily pigmented uveal cyst.

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Figure 3. Grouse’s other eye, which shows a small cyst settled on the ventral aspect of the anterior chamber.

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Figure 4a. Multiple uveal cysts are stuck to the corneal endothelium in this patient.

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Figure 4b. The same patient as in Figure 4a. Note how the pigment deposited by the uveal cysts on to the corneal endothelium is partially blocking the bright green fundic reflex, allowing good estimation of how much the dog’s visual axis is impaired.

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Figure 5. Focal corneal ulceration associated with endothelial dysfunction due to deposition of uveal cyst pigment.

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