The lens of a dog's eye is a solid disk located in the center of the eye. It's located in the iris (the colored part of the eye), and you usually don't see it because it's completely transparent, like glass. When light enters the eye, it passes through the pupil and the area behind the eye (light on the nerves). The lens is an important part of the eye. When it changes shape, we can see at different distances.

As a dog ages, changes will occur within the body. Maybe it has less energy, becomes a little fatter, or maybe develops a little arthritis and changes inside the eye. Moreover, the core will continue to harden, begin to become less transparent, and more "yin" parts will appear. This hardening causes cloudiness. This is a gradual process that generally does not cause vision problems and is called nuclear sclerosis.

Older dogs are more likely to develop cataracts than younger dogs, possibly because older dogs are exposed to more things that can damage their eyes over time. Cataracts can form for a variety of reasons, including radiation (or light), injury, malnutrition, genetics, and diabetes, all of which increase the risk of developing cataracts.