Yes, I'd isolate it and treat it for popeye. I looked up popeye on the Tropical Fish Forum page, and this is what it said:
"SYMPTOMS: One or both eyes protrude from the socket. This may be caused from, fighting, bacteria, tumor or over-aerated water. If left untreated, the eye may bulge out so far that the eye can pop out of the socket, resulting in the loss of an eye.
"TREATMENT: If it was caused by over-aeration, turn the power head water stream adjustment to its lowest setting. Temporarily shut off the air to the power heads, and allow the air pump to be the only source of air. Observe the Popeye for a few days, if this was the problem, the eye should begin to recede. If no improvement is noticed, it may be because the problem is bacterial. Medications that may help are Furan, Kanamycin Sulfate, Tetracycline and Maracyn-Two. Treatment in a hospital tank is recommended. "
Just make sure that if you medicate, the treatment is safe for scaleless fish--cories can be touchy. And absolutely no salt!
Hope this helps.
-- Pat