it may be a small scar but it could also be a small ulcer or foreign body. I would advise you take the dog to the vet and get the eye stained. ulcers are not to be trifled with, they can very quickly progress to serious, intractable problems and lead to the loss of the eye. The sooner they are treated (correctly) the more reliable the outcome. Fingers crossed its just a small scar, but best get it checked.