My Left Eye Started Sinking into my Eye Socket Years Ago & It Looks Like Its Sunken in More Since. What is Causing This? (photo)

In my opinion based upon the two posted photos you have a familial, genetic family very slight asymmetry. As for definitive diagnosis of enopthalmos might be a stretch. Best to be seen in person by boarded PSs in your city. If indicated and you can afford the 3-D scan of your orbital anatomy you can pre sue the definitive diagnosis. Otherwise try a filler or fat grafting or even minor surgery to attain better symmetry. Again the degree of asymmetry is very minor in my opinion based on the info and photos posted.