Cataracts primarily form in which part of the eye?

Cataracts primarily form in the lens of the eye. The lens is a transparent structure that focuses light onto the retina, allowing for clear vision. Over time, various factors such as aging, genetics, and exposure to UV light can lead to changes in the lens's structure, causing it to become cloudy, which is what characterizes a cataract. This clouding obstructs the passage of light and can lead to vision impairment.

The other parts of the eye mentioned—such as the cornea, retina, and iris—serve different functions. The cornea is responsible for the majority of the eye's focusing power and does not typically develop cataracts. The retina is the light-sensitive layer at the back of the eye that processes visual information, while the iris controls the amount of light entering the eye. Therefore, cataracts specifically affect the lens, which is essential for maintaining clear vision.