There are a couple medical conditions that can lead to cloudy eyes in a dog, including nuclear sclerosis and cataracts.
Nuclear sclerosis is a benign condition occurring in senior dogs due to their lens fibers becoming denser and scattering light. Typically, the eye will appear only mildly hazy or bluish, and this condition does not affect vision. It occurs in all older dogs and usually, no treatment is needed.
On the contrary, a cataract develops as proteins accumulate within the lens of the eye due to a disease or genetics. This is a progressive condition, which means it worsens over time. A cataract starts out incomplete (the cloudiness only covers a portion of the lens) then progresses to cover the entire lens. In a mature cataract, the lens appears opaque or white in color. One or both eyes may be affected. Cataracts ultimately result in blindness and can be particularly painful.
Dogs that are genetically predisposed to cataracts tend to develop them at younger ages. However, dogs who have diabetes develop cataracts due to dysregulation of glucose, which can occur at any age. Once mature cataracts develop, there is no treatment aside from surgery. However, anti-inflammatory medications may be prescribed by your veterinarian to help manage pain and inflammation.
If an eye condition is suspected, your veterinarian can perform a thorough exam and discuss appropriate next steps for your pet.