What condition is characterized by clouding of the eye's lens?

Cataracts are specifically characterized by the clouding of the eye's lens, leading to a decrease in vision. When the lens becomes cloudy, it obstructs the passage of light and can cause blurred or dim vision. This condition is typically age-related but can also result from other factors such as injury, certain medications, or prolonged exposure to ultraviolet light.

In contrast, glaucoma involves damage to the optic nerve often related to high intraocular pressure, not clouding of the lens. Macular degeneration affects a different part of the eye (the macula) and leads to loss of central vision but does not involve the lens. Presbyopia is related to the eye's gradual loss of the ability to focus on nearby objects, largely due to aging, but does not cause clouding of the lens itself. Thus, cataracts are uniquely identifiable by their characteristic cloudiness of the lens, making this the correct choice for the question.