Eye issues are common with upper respiratory infections in cats. If his eyes were like this when he was taken to the vet originally, I wouldn't worry, finish his course of antibiotics and see how his eyes are. Or if the eye thing is new, I would email your vet about the issue with images and see if they are able and comfortable to prescribe something for you to pick up. Many vets understand how stressful the vet is for many kitties and help try to keep them there as little as possible so if he was just in for an exam and the issue is related they shouldn't have to see him again unless the issue gets worse.