Nuclear sclerosis is an age-related change in the density of the crystalline lens nucleus that occurs in all older animals. It is caused by compression of older lens fibers in the nucleus by new fiber formation. The denser construction of the nucleus causes it to scatter light. Although nuclear sclerosis may describe a type of early cataract in human medicine, in veterinary medicine the term is also known as lenticular sclerosis and describes a bluish-grey haziness at the nucleus that usually does not affect vision, except for unusually dense cases.
Nuclear sclerosis occurs when the linear fibers in the lens become compressed as new fibers continually form and push them toward the center. Compression causes the center, or nucleus, of the lens to grow thicker, leading to a cloudy appearance.
Symptoms include a change in pupil color from black to gray or bluish white and mild visual impairment later in life. Color change usually affects both pupils simultaneously.
Veterinarians can diagnose nuclear sclerosis during routine eye exams. Pupil dilation can help determine whether a dog has this condition or cataracts.
Nuclear sclerosis does not require medical treatment. Safety measures, such as blocking off stairs and supervising dogs that are outdoors, should be taken if visual impairment occurs.
In veterinary practice, nuclear sclerosis is a consistent finding in dogs greater than six years old. Nuclear sclerosis appears as a bilateral bluish-grey haziness at the nucleus, or center of the lens, caused by an increase in the refractive index of that part of the lens due to its increased density. It is often confused with cataracts. The condition is differentiated from a cataract by its appearance and by shining a penlight into the eye. With nuclear sclerosis, a reflection from the tapetum will be seen, while a cataract will block reflection.