What condition is characterized by clouding of the lens?

Cataracts are a condition specifically defined by the clouding of the lens of the eye. This cloudiness can impede vision, leading to various visual disturbances such as blurred vision, difficulty with glare, and an overall reduction in visual acuity. Cataracts develop gradually and are commonly associated with aging, although they can also arise from other factors, including diabetes, certain medications, or prolonged exposure to UV light. The clarity of the lens is essential for proper vision as it helps to focus light onto the retina.

In contrast, the other conditions listed—Parkinson's Disease, Huntington's Disease, and Alzheimer's Disease—primarily involve neurological dysfunction rather than direct effects on the eyes or vision. While some of these diseases may lead to secondary visual issues or other complications over time, they do not primarily manifest through the clouding of the lens, which distinguishes cataracts as the accurate answer in this context.