do you have pictures. maybe the cornea or sclera was scratched by one of the other turtles. might need some medication. you can try to flush it with saline solution.
ILL try to get some pics, it very well could be a scratch because the albino I just got has some reallly long claws right now. Would warming the water up help at all?
for now bring the heat up to around 80. go pick up a sulfa block for the water.( those white turtle shaped things) i think tetra makes them. 1 per 20gallons of water if the tank is less it will still be ok. that will help if there is any bacteria or fungus growing.
when my turtles get eye problems, it usually turns out to be bacterial infection. I have seen scratches, but the only definite one blinded one of my pseudemys in one eye. Use sulfa and take it to an exotics vet.