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CANINE DISEASES
Cataract
Cataracts are an opacification (developing cloudiness) of the lens within the eye. The lens is situated behind the pupil (black hole in the centre of the eye) and allows the eye to focus vision. Cataracts should be differentiated from nuclear sclerosis, which is the cloudy-blue appearance of a lens that may be seen in older dogs, especially those over 7 years of age. Both look similar, but nuclear sclerosis is a normal change with age and although the lens appears cloudy the vision will not be greatly affected. With cataracts however there is impaired vision of varying degrees.
Cataracts may be a result of any of the following causes:
- Trauma
- Degeneration of the lens secondary to glaucoma (increased eye pressure), uveitis (inflammation within the eye) or any other ocular (eye) disease
- Pups on milk replacer diets that are deficient in amino acids
- Metabolic disturbances such as diabetes mellitus, hypocalcaemia (low blood calcium) and hypoparathyroidism (lowered activity of the gland that regulates the calcium levels in the body)
- Inherited condition in some purebred dogs which may start to be evident as early as 8 weeks of age The breeds more common effected include Afghan hound, Beagle Bernese Mountain Dog, Boston Terrier, English Cocker Spaniel, English Springer Spaniel, German Shepherd, Golden Retriever, Maltese, Miniature Schnauzer, Old English Sheepdog , Rottweiler and StandardPoodle.
A retroillumination examination is used to differentiate cataracts from nuclear sclerosis. This involves shining light into the eye and evaluating if light reflecting off the back of the eye is being obstructed, which would be the case if cataracts are present.
The prognosis (outlook) for cataract development can be generally related to the position of the cataract within the lens. Nuclear cataracts are those that occur in the middle of the lens and they will not progress. Posterior opacities (on the back of the lens) will also not tend to progress. Equatorial cataracts (those at the edges of the lens) can progress to the point where they extend throughout the entire lens. Anterior cataracts (on the front of the lens) show variable progression.
The aim of treatment is to manage the initial cause of the cataract and then to surgically remove the cataract. Electroretinography, which is a diagnostic technique to measure the function of the visual receptors in the eye, is often undertaken prior to surgery to determine whether near normal vision can be expected after removal of the cataract. Recently a major advance in cataract surgery has been a technique called phaco-fragmentation. This technique uses ultrasound to break up the cataract into small particles that can then be removed by suction. This technique has a success rate in excess of 90%.
Related sites
Animal opthalmology
Good information on surgical treatment
Veterinary vision
Good surgical description with diagrams
Animal Eye Specialists
Detailed description of surgery with photos
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