"That was just from our brief exposure," Hargrove says. "Imagine the whales always having to swim through it."
The mucus secreted by the eyes of the killer whales -- whether it's triggered by chlorine, more frequent exposure to the air, or other factors of captivity, like looking up into the sun more often, or even all of the above -- appears to offer some protection. There is no obvious trend (according to the trainers I have spoken with) of older killer whales predictably developing sight problems in captivity.
But that's not true for all captive marine mammals, I learned. Pinnipeds, like sea lions and walruses, apparently do not have the effective eye protection sported by killer whales, and routinely suffer from premature cataracts, corneal disease, and lens issues. According to one study, chlorine and water treatment chemicals play a role, but sunlight is a key causative factor. The study explains:
"[C]aptive pinnipeds are frequently housed in pools painted a light blue color which is very effective at reflecting most of the UV light energy back towards the animals as they dive and swim. As well, captive pinnipeds are often housed in deep grottos or pools where they must look up frequently to see out of the exhibit or to catch fish.... When keepers, trainers, or members of the public feed the animals they may inadvertently force the animals to look directly into the sun to get their fish reward. These conditions may cause damage to the eyes of captive pinnipeds because they are forced to be exposed to far more UV light than their wild counterparts. This is supported by studies such as a recent publication that identified pinnipeds with no access to shade were 10 times more likely to develop cataracts or lens luxations."