Just because his eye is closed does not mean he is blind. How long has it been closed like this??? I would try flushing the eye with PLAIN saline solution. The kind that is used for contacts. There could be something possible caught in the eye. It could be a Vitamin A deficiency causing it. Do you use a multi vitamin? What do you gutload your feeders with? Lastly, it could be some type of infection. If the flushing does not work, I would get him to a vet. If it is some type of infection and you leave it untreated, then he could eventually lose his sight in that eye.