My issue is so specific.  I do use Retin A and have used medication for rosacea, but never on or near my eyes.  I use the generic for Latisse, Careprost (been doing it for about two years).   I have beautiful, thick, long lashes on my left eye, and on my right, long lashes (not as thick) except in about a quarter inch patch just to the right of center of my lash line.  There, the lashes are extremely and noticeably sparse and short.  Not an earth shattering problem, but very puzzling. Overall, I'd say the Careprost hasn't had as much effect on my right lashes, though in the places other than the sparse patch, they are pretty good.  Prior to starting Latisse/Careprost, I had a single experiment with eyelash extensions, and pulled out quite a few lashes getting them off (and assumed they'd grow back)--that is in fact why I started the Latisse--to boost the regrowth.  Prior to the extensions, I had pretty nice lashes, no problems (darn that Groupon!). Oh and I had permanent eyeliner done about a year and a half ago and had no issues with it.  BTW, I'm 62 and do HRT.  What do you think could be causing that little bare patch?