I'd be very grateful to receive your answers to these questions or to have a pointer to a thorough on-line paper on this important health issue. In shar pei dogs, the weight of the folds and tissues around the eyes leads to entropion. This may also be the problem for chows. Obesity, scarring from injury and skin infections and probably other stuff all can cause entropion. We have seen it a couple of times as a sequelae to temporomandibular myositis, too.
Corneal pigmentation seems to be a defense mechanism against chronic irritation.
If you look at dogs with chronic skin disease most of them have increased skin pigment, too. It does not always clear up but there can be considerable improvement with correction of the entropion. I think that irritation does tend to worsen the entropion because it makes the lid thicker due to inflammation, which can make the problem worse. Once in a while we have dogs and cats with very mild entropion who do OK as long as we use anti-inflammatory eye medications occasionally. This doesn't happen often enough that anyone can count on it working, though.