POV "teardrop" effect

I'm filming a POV shot and the character is crying.
Does anyone know how to make a teardrop 'well up' on the bottom of the screen (eye)?

I'd probably do it with a polygon to mask the effect, probably very soft since I don't think it's even possible to focus your eye on your own eyelid. Blur, desaturate, and maybe use a Fast Noise as the input on a Displace node to simulate refraction through the tear.

Thanks, I'll try that.