Leah is described as having weak eyes (Genesis 29:17). This is a strange description, and I can’t help but think that it means she just looked generally unhealthy and dull. Leah paled in comparison to Rachel. Laban tricks Jacob into marrying the weak-looking woman along with the pretty one.
In Genesis 30:31-43, another agreement is made where Jacob will receive the weaker looking goats. Jacob pays Laban back, though, by making sure more goats come out looking undesirable, while being stronger in actuality. Jacob makes sure that his flocks, while looking like Leah, are actually like Rachel, and he gives all the weak flocks back to Laban.