I don't have Pro just P6 and I posted on the forums over a year ago about the same issue. the eyelashes appeared clumpy or sparse or like blurred dots. I was told to use settings of...

Min shade rate 0.2
Pixel Samples to 5
Max Texture size from 1k-4k
Then reload textures after changing the setting and then render.

That did help for me. Now that's with P6, I'm sure those settings are the same with each edition?