I have a sigma in my eye
A few times a year I get those curious prescription wearers that want to know, "My eye doctor says I have a sigma. What is that?" Your knowledge on this and the ability to explain this in a way understandable to them is a great way to show your understanding of prescription analysis and caring/communication skills. I tell them it is called astigmatism. It has to do with the shape of your cornea. If you think of a basketball. It is a sphere, so it has the same curves all the way around in every direction. A football has a long radius and a short radius. This causes the need for an altered Rx in these areas. I will associate this with their Rx from the doctor. They may not understand this completely, but will be satisfied with the fact that you took the time in explaining this to them. It can leave a lasting impression for some and many tell me "no one ever explained that to me." Even after wearing eyeglasses most of their lives.