A cataract is an opacity of the lens or its capsule. The transparency of the lens depends upon its relatively dehydrated state, lamellar arrangement of lens fibres, solubility of lens proteins and smooth/uniform lens capsule. The lens is avascular and depends upon the integrity of the lens capsule and anterior epithelium for the majority of its metabolic needs. Injury to the capsule and/or anterior epithelium can result in metabolic changes and derangement of the lens transparent state. Insults to the lens can lead to death of cells and lens fibres, abnormal cell proliferation, and disruption of relatively anhydrous state which leads to localized water accumulations, vacuolation and local precipitation of soluble proteins, and deposition of crystals/aggregates.
In dogs and cats, cataracts can be inherited (juvenile or later onset), or secondary to systemic disease or ocular abnormality, eg uveitis. In rabbits it is commonly due to Encephalitozoon cuniculi infection but can also be congenital. Other causes of cataracts can include diabetes, ocular disease, trauma, etc. In exotic species such as ferrets, guinea pigs and reptiles, cataracts are often age-related, but can also be congenital. The cause of cataracts in horses can be difficult to define in many cases, but can be developmental (eg congenital, hereditary), degenerative (eg senile) or acquired (eg secondary to ocular disease). Congenital cataracts in cows are usually caused by the bovine viral diarrhoea virus or can be an inherited autosomal recessive defect.
To find out more on this topic, watch out for The Webinar Vet’s latest webinar on Cataract. As a general practitioner, what can I do about it? by Ron Ofri DVM PhD DipECVO on the 30th May at 8.30pm.
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