If someone has a cataract in their right eye, their lens is cloudy rather than clear, so they have difficulty seeing. Luckily, cataracts are easily removed.
Cataracts, cloudy areas of the lenses of the eye, are often associated with old age. Cataract can also mean a large waterfall, like Niagara Falls. Even with cataracts, you can still make out a cataract. It's not a little waterfall; it's huge!