Castor oil's benefits are mostly making the hair smoother by coating it, which reduces breakage. I don't think that it is clinically proven to help lashes "grow", but some people say that they noticed the hair gets less sparse thanks to improved blood circulation to the area. I'd say your best bet is massaging it in the area for a few minutes, and hopefully you end up noticing results! It's a bit of a heavier oil so if you want something lighter i'd point you to the ordinary's serum.