Lens

a transparent, biconvex structure in the eye that helps to refract light to be focused on the retina

The lens is a transparent, avascular organ surrounded by an elastic capsule. It is suspended behind the pupil by zonular fibres and confined by its own basement membrane. The lens continues to life-long fiber cell proliferation. 

The lens is avascular and depends on the uvea, aqueous humor, and vitreous for its metabolic needs. Its function depends on its transparancy and ability to refract light.

Cataracts

A cataract is a change in the clear protein of the lens.  When some of this protein becomes abnormal it becomes crystallized and opaque.  This opaque area distorts the image and blurs the image slightly.  As the cataract gets larger more and more of the image becomes distorted until vision is affected.  Surgery is the only method of improving vision in a patient with cataracts.  (FAQ on Cataracts)

Diabetes Mellitus

Diabetes Mellitus is a common endocrine (hormonal) disease that affects both dogs and cats. It occurs more commonly in middle aged to older animals. Female dogs are more likely than male dogs to get diabetes, while male cats are more prone than female cats. Dog breeds that are more at risk include Beagles, Cairn Terriers, Dachshunds, Miniature Pinschers, Miniature Schnauzers, Poodles and Pulis. No specific cat breed is more predisposed than another. (FAQ on Diabetes Mellitus)

Lens Luxation

The lens of the eye normally lies immediately behind the iris and the pupil, and is suspended in place by a series of fibers, called zonular ligaments.  When partial or complete breakdown of the zonular ligaments occurs, the lens may become partially dislocated (Lens Subluxation) or fully dislocated (Lens Luxation) from the lens’ normal position.  Surgical removal of the lens can be beneficial. Medical treatment of inflammation and glaucoma can relieve discomfort. (FAQ on Lens Luxation)

Nuclear Sclerosis

Nuclear sclerosis is a normal aging process of the lens.  The lens within the eye slowly lays down lens fibers in layers at its outer edge throughout life.  Once the lens has reached its maximum size, lens fiber layers become compressed toward the center making the lens harder and more optically dense.  As the lens becomes increasingly dense, it traps more blue light giving the impression of a pathologic cataract.  Nuclear sclerosis does not need to be treated. It is a normal aging process and will not clinically affect vision in most animals. (FAQ on Nuclear Sclerosis)

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