The symptoms of cataracts are diverse. Firstly, the most primary manifestation is a decline in vision, which is a painless and gradual decrease. Unlike glaucoma, where the decrease in vision is accompanied by swelling pain in the eyes and even headaches, the vision decrease in cataracts occurs gradually and not suddenly. If the onset is sudden, then it is generally not considered to be caused by cataracts. Besides the painless, gradual decline in vision, some patients may experience a decrease in contrast sensitivity, and changes in refraction. For example, patients who have presbyopia might find that their presbyopia diminishes and their nearsightedness worsens if they develop cataracts, particularly nuclear cataracts. Some people may experience monocular diplopia or polyopia, as well as varying degrees of visual field defects.