You know what a “cataract” is in nature. It’s a great waterfall or downpouring of water. Now why should a certain kind of eye trouble also be called a “cataract?”

This is because in ancient times it was believed that this particular eye trouble was caused by an opaque film that came down like a cataract over the lens of the eye. A cataract of the eye is simply a cloudy or opaque discoloration within the lens of the eye. It may or may not interfere with vision. In fact, many people may have cataracts without knowing it.