I am about 70% certain the author is personifying the eye sickness. A degree of certainty above that would be Far too pathetic even for jap penmanship.
Like when you ask a kid how it's hurt it's knee it goes into deepest lore, and then suddenly stops with a NO.
Then you're 70% wrong. Cataracts are another, older, name for powerful waterfalls of any kind (derived etymologically from Greek katarhaktēs), but especially those that surge with great power over a precipice; the eye condition is actually derived from the components that make up that compound word ("kata-" meaning "down" and either "arhattein", meaning "to strike hard" (in which case the compound is kat-arrhattein), or "rhattein", meaning "to dash, break") being applied to portcullises, which were designed to slam down hard and break entry into whatever place they were set above, and also act as an obstruction for line of sight; thus, when your eyes film over, cataracts.
Bonus fact, there are many undersea cataracts that govern the flow of ocean currents, and are in large part why life can survive in many places of the ocean that would otherwise be desolate.