As I wrote, the reason for the higher CYA for an SWG pool is to reduce the rate of pH rise by reducing the rate of chlorine consumption thereby letting you lower your SWG on-time.

If you are not experiencing a pH rise that you find intolerable, adding a lot of acid every week, then you can certainly leave your CYA at 50 ppm and keep your FC at least at 2.5 ppm if not 3 ppm minimum. That's perfectly fine and is totally up to you. I was only explaining why a higher CYA is usually done in most SWG pools -- it is a legitimate reason that works well in most cases.

Yours, however, is the only case of stinging eyes from tens of thousands of pool owners that is not attributable to either chloramines (usually from low FC relative to CYA) or an out-of-whack pH. There are many pools with very high CYA levels -- even over 200 ppm in pools using only stabilized chlorine -- and stinging eyes aren't a direct result, though indirectly if the FC is low and Combined Chlorine (CC) is present then stinging eyes are reported. Your experience is very real and there is no question about that -- it may be the CYA or it might not be. Chemical sensitivity is a unique experience and perhaps you have a sensitivity to this chemical.

Also keep in mind that pool store tests are very often wrong. I would only trust your own testing. Though the pool stores usually don't get the pH that wrong (though sometimes they do), they very often get the CYA test very, very wrong. It could have been far higher than 100 and you could have very likely had high chloramine levels as a result. This should not happen if you maintain a higher FC with the higher CYA -- i.e. 4 ppm FC with 80 ppm CYA, but again you do not have to do this -- it's completely up to you.