Which condition is characterized by clouding of the eye lens?

Cataracts are characterized by the clouding of the eye lens, which leads to a decrease in vision. This condition occurs when proteins in the lens of the eye begin to break down and clump together, causing a cloudy area that disrupts the passage of light. As cataracts progress, individuals may experience symptoms such as blurry or dim vision, difficulty with night vision, and changes in how they perceive colors.

While other conditions listed might also affect vision, they have different underlying issues. For example, presbyopia is related to the aging process of the lens that affects the ability to focus on near objects due to loss of elasticity. Glaucoma refers to a group of eye conditions that damage the optic nerve, typically associated with high intraocular pressure, and muscular degeneration refers to changes in the macula of the retina, affecting central vision. Thus, the defining feature of cataracts is the clouding of the lens, making it the correct response to the question.