Why it happens: Being nearsighted, farsighted, or astigmatic — having an irregular curve in the cornea that causes blurriness — are the chief reasons you see glare or halos at night, especially around headlights and traffic signals.
How to Fix it: Get your prescription checked. If new glasses don't help, make sure the lens is aligned with the visual center of the eye (to reduce distortion).
Red Flag: A posterior subcapsular cataract can cause a loss in night vision or bothersome nighttime glare. It's more common in diabetics, people who've been on steroids, and those who have experienced eye trauma. If you can't see well at night, ask your doctor to rule out this type of cataract.
Why it Happens: Floaters are tiny threads or specks floating across your field of vision. "They're nothing more than shadows cast by small strands and bits of protein in the jelly of the eye," says Lessner. As you age, that jelly liquefies and separates from the retina.
How to Fix it: Floaters by themselves are not harmful, and usually no treatment is necessary.
Red Flag: Dozens or hundreds of new floaters can signify a retinal tear or detachment, which can lead to blindness if not corrected immediately. You will likely need surgery that same day to repair the damage.