MSD

I googled 'mercury tuna' and found this as the first result.
http://www.nytimes.com/2008/01/23/dining/23sushi.html
I'm quite glad that I went from having 12-18 pieces of sushi a week to almost none in the past few months. At the advice of my pediatrician when I was 17, I keep myself to having one can of tuna every two weeks, at most, even though I could probably do two a week at my size without exceeding FDA safe limits.

I used to have a can two or three times a week, especially when I was staying with my grandmother while in college. My vision is still around 20/15 in both eyes, so I'm going to guess that what snowy found on taurine deficiency is probably the answer. I'm at no risk of visions loss there considering my energy drink intake through college (although it didn't help my blood pressure much.)
Too late