Chapter 8 Lens
Most pathology that affects the lens, aside from rare congenital defects, is described as a cataract. A cataract is an opacity in the lens that can vary from a small defect visible only under magnification to an opacity that affects the entire lens and causes blindness. Most cataracts in dogs of any age are hereditary. Diabetic cataracts are also fairly common. Most cataracts in cats are secondary to uveitis.
Descriptions of cataracts include the location of the cataract, the causes of the cataract, and the stage of cataract development. Early, small opacities that do not interfere with vision and may not progress are referred to as incipient. Cataracts that are immature involve more of the lens and, depending on their size and location, may affect vision. When the entire lens is involved and no tapetal reflex is seen through the lens, the cataract is called mature. Immature and mature cataracts can liquefy, and lens proteins can leak out of the lens capsule, leading to shrinkage of the lens. At this stage the cataract is called hypermature.
Figure 8-5 Nuclear sclerosis. The nucleus of the lens becomes sclerotic with age and is visible as a circular area of “frosted glass” inside the “clear glass” of the lens equator. No visual impairment occurs in animals.