Accepted Answer

It may be that one of his nictitating membranes is always a little more pronounced on one eye, but sometimes it can just appear that way due to pigmentation. Whichever way, that is not important.
Prolapse of these membranes does not always imply an irritation in the eyes (although it can). That is why I asked if there was a discharge. Lack of discharge makes it unlikley we have any inflammation of the eye.
Most likely here the membranes have slid accross because he is slightly unwell. This does not necessarily mean anything serious. Just like us, dogs can have öne of those days". It can happen after heavy exercise, emotional trauma and heat stress for instance. I often see it in dogs with no evidence of any other problem. It is usually transient (24 hours).
Because your dog is well otherwise I suggest you just monitor him and hopefully it will clear and that is the end of it. If on the other hand it progresses or he shows other signs of ill health then you should get him checked over by your vet.
Regards, XXXXX

Expert:	Dr Pete
Pos. Feedback:	99.7 %
Accepts:
Answered:	11/26/2008

Dog Veterinarian

Bachelor of Veterinary Science (University of Melbourne, Australia)