THE WARMER weather is just around the corner for many of the dairying regions in Australia. The longer summer days can bring new animal health concerns, one of which is cancer eye. This article discusses the most common types of cancer eye in cows as well as their treatment and prevention.
What is cancer eye?
The most common type of tumour or ‘cancer eye’ in cattle is squamous cell carcinoma.
This type of tumour is very invasive and can rapidly spread to the surrounding ocular tissues. The condition is of extreme economic importance, representing 58 per cent of all cancers that result in condemnation of mature cattle slaughtered and 33 per cent of total condemnations in mature cattle (Australian Quarantine Inspection Service, NSW, 2010–2014).
Herd prevalence varies from one to 20 per cent and is associated with certain risk factors such as breed, pigmentation, age and exposure to sunlight (UV radiation).
Cattle with non-pigmented eyelids and conjunctiva (white-faced cattle) are at increased risk and the disease occurs most commonly in Herefords and white-faced Holstein Friesian cattle. Cancers usually start on the unpigmented skin but can spread to pigmented areas.
Older cattle are more susceptible to cancer eye, with the disease being uncommon in cows under five years of age. This is likely related to the increased exposure to other risk factors such as sunlight.
Viruses have also been implicated but their importance in the disease is not fully understood.
How is cancer eye identified?
The tumours are found most commonly on the third eyelid, the upper and lower eyelid margin and on the eyeball itself (most frequently where the white of the eyeball meets the clear part of the eyeball, called the limbus).
There are four common appearances of cancer eye, three of which are benign and the fourth being highly malignant, meaning it has the ability to spread to adjacent and underlying tissues.
- Plaque (benign): Small, circular, white elevation on the surface of the eyeball.
- Keratoma (benign): Hard, raised growth on the eyelids, often with discharge and debris.
- Papilloma (benign): A wart-like growth.
- Carcinoma (malignant): Nodular and cauliflower-like. Commonly is bloody, ulcerated, friable, and foul smelling. Can initially appear as one of the other benign forms of cancer eye or can simply arise without any of the benign stages.
The benign forms can sometimes regress but the malignant form will progressively grow and invade the entire eye socket and surrounding structures.
How is cancer eye treated?
Treatment must be prompt, aggressive and performed by a veterinarian. The success of treatment is highly dependent on the location of the tumour and invasion of surrounding tissues.
Tumours can be surgically excised, either in isolation or may involve a more radical procedure such as ablation of the entire eyeball. Surgical excision does not guarantee a cure and a high recurrence rate can be expected in some cases (40 to 50 per cent). Your veterinarian will check the lymph nodes of the head and neck prior to any treatment to help give a prognosis.
Cryotherapy (effectively freezing the tumour off with a cryogen such as liquid nitrogen) is also utilised by some veterinarians and is a very useful therapeutic tool. This method works well on small tumours (less than 2 cm diameter) on the eyeball itself but can leave a scar on the surface of the eye that may interfere with future vision.
Another therapy involves exposure of the tumour to ionising radiation such as strontium-90.
Prevention and control of cancer eye
Routine inspection of all cows (aged more than three years old) allows early detection and treatment of cancer eye.
It is important to always check both eyes as about 30 per cent of affected animals will have lesions on both eyes and sometimes multiple lesions on one eye.
Identification of plaques, papillomas and keratomas is preferable as these early stages are much easier to treat and have a better prognosis.
All treated animals should be closely observed on a regular basis for recurrence.
Early culling of affected animals is a viable option due to the risks of recurrence and subsequent rejection of the carcase at slaughter. Severely affected animals should be humanely destroyed as soon as possible to minimise discomfort and suffering.
In the long-term, cancer eye can be effectively controlled by selection for pigmented eyelids. Eyelid pigment is present at birth, while eyeball pigment usually takes more than five years to fully develop.
Both are highly heritable and appear to be genetically related, thus selection for one effectively selects for both.