What condition of the eye results in a cloudy or opaque lens?

The condition that results in a cloudy or opaque lens is cataract. A cataract occurs when the proteins in the lens of the eye begin to break down and clump together, causing the lens to become cloudy. This cloudiness impedes the passage of light through the lens, leading to blurred vision and, if untreated, can result in significant visual impairment.

Cataracts develop gradually and are often associated with aging, but can also occur due to other factors such as diabetes, prolonged use of certain medications, or exposure to ultraviolet sunlight. The only definitive treatment for a cataract is surgery to remove the cloudy lens and, in most cases, replace it with an artificial lens.

Glaucoma, macular degeneration, and retinopathy involve different parts of the eye and result in various visual impairments, but they do not specifically cause the lens itself to become cloudy or opaque as cataracts do. Glaucoma primarily affects the optic nerve usually due to increased intraocular pressure, while macular degeneration affects the central part of the retina, and retinopathy involves damage to the retina's blood vessels.