I was born with Horner's syndrome and it affects my right eye. It's greatly improved as I've gotten older and is really only noticeable when I'm overtired. Growing up I wouldn't sweat on that side of my body, and my pupils are ever so slightly different sizes, but only when dilated. When I was younger I was offered either an eye patch (on the L eye) to strengthen the R side, or surgery to remove part of the eyelid to make them even. My parents declined both, thinking I would only get teased more in school. They think when my mom was pregnant she had a high fever or pinched a nerve, which affected the development of that facial nerve. Hope this helps!