The loss of clarity in the crystalline lens of the eye is called a cataract. Normally the substance of the crystalline lens is absolutely clear, and light passes unimpeded through the lens, to be focused on the retina at the back of the eye.
Two major types of cataracts are known:
juvenile and mature
The juvenile form usually occurs rather suddenly and prior to the eighth year of life. The mature form develops much more slowly and is usually seen in dogs at least 9 or 10 years old.
It is unusual for schnauzers to develop juvenile cataracts, but if they are see, your vet should be examined by a qualified vet, skilled in the treatment of eye diseases.
Unless there are secondary changes within the eyes, such as glaucoma, little need be done to treat mature cataracts. They are a result of the gracefully aging dog.