If you have acuity of vision, it means that you are less likely to wear prescription glasses. The reason is that "acuity of vision" is a term used to refer to the clarity of vision. So, if you possesse acuity of vision, your sight is fine. However, if you have low acuity of vision, it is more likely that you will need prescription glasses.
Well one reason why they struggled was because the priest had higher authority than the king himself did but I don't really know why or how it lead to the crusades in the holy land. I'm sorry I couldn't help you fully but I tried.
