Hereditary Cataract

What is hereditary cataract?

A cataract is an opacity of the lens, the normally transparent structure inside the eye that focuses light onto the retina. Hereditary cataract (HC) is a cataract that occurs as a result of an inherited genetic predisposition rather than from injury, inflammation, or ageing. It is one of the most commonly certified conditions under the BVA/KC/ISDS Eye Scheme.

The lens changes seen in hereditary cataract vary considerably between breeds in their position within the lens, their pattern, the age at which they appear, and the rate at which they progress. In some breeds, the cataract is congenital (present from birth or very early life) and may progress rapidly to total opacity and blindness within months. In others, it develops in middle or old age and may remain partial throughout the dog's life with little effect on vision.

Breeds affected

Hereditary cataract is certified under the BVA scheme in more than 20 breeds. Each breed has a specified age range during which hereditary cataract is considered most likely to be of hereditary origin. The breeds currently on the scheme include the Alaskan Malamute, Australian Shepherd, Belgian Shepherd Dog (all varieties), Bichon Frise, Boston Terrier, Cavalier King Charles Spaniel, French Bulldog, German Shepherd Dog, Giant Schnauzer, Irish Red and White Setter, Large Munsterlander, Leonberger, Miniature Schnauzer, Norwegian Buhund, Old English Sheepdog, Standard Poodle, Chesapeake Bay Retriever, Golden Retriever, Labrador Retriever, Siberian Husky, American Cocker Spaniel, Welsh Springer Spaniel, and the Staffordshire Bull Terrier.

DNA testing

For several breeds, a DNA test targeting a mutation in the HSF4 gene is available. This test is relevant to the Staffordshire Bull Terrier, Boston Terrier, Australian Shepherd, and Miniature Schnauzer, among others. However, not all hereditary cataracts in these breeds are caused by the HSF4 mutation, and DNA testing does not replace clinical examination. For breeds where no DNA test is available, clinical examination under the BVA scheme remains the primary screening tool.

What the examination involves

The examination requires pupil dilation with tropicamide drops to allow full visualisation of the lens. The panellist examines the lens using slit-lamp biomicroscopy, assessing the position, shape, density, and extent of any opacity. Both eyes are examined. Your dog's eyes will be light-sensitive for several hours after the drops, so plan accordingly for the journey home.

Not all lens changes seen on examination are hereditary cataracts. Temporary opacities around the lens sutures, nuclear rings, and the normal lens clouding of old age (nuclear sclerosis) must be distinguished from true hereditary cataract. An experienced panellist will be able to differentiate these findings.

When to test

Annual examination within the age range specified for your breed is the standard recommendation for any dog being used for breeding. The age ceiling for each breed represents the point beyond which a newly developing cataract is considered less likely to be of hereditary origin, though this does not mean examination is without value after that age.

A final eye examination at or after eight years of age is recommended for all dogs that have been used for breeding, to check for late-onset inherited disease and to provide evidence of clear breeding lines.