[[1]] is clouding of the normally clear lens of the eyes.

Cataract is the clouding of the normally clear lens of the eyes. 

• Sometimes, particularly in old age, eyesight becomes foggy. It happens because the lens of the eye becomes cloudy. When it happens, the person is said to have cataract.
• In severe cases, it can lead to loss of vision. It can be treated with a procedure where the natural lens of the eye is replaced with a new artificial lens. 

Hence Cataract is the correct answer.