Possible Clues:

• Fall that impairs vision
• It's hard to see through all that water
• Downpour makes it hard to see
• Steep descent of a river
• Waterfall — eye problem
• Problem with vision producing fall
• Downpour that makes it hard to see?
• Drop what may have a bad effect on the viewer
• Eye problem - waterfall
• It's such a downpour we can't see through it