Can face primer be used as eye primer as well?

It can be, but it's better to buy an actual eyelid primer (thicker consistency and better lasting power than face primer). If you're looking for affordable options, the best face primers are Hard Candy Sheer Envy Skin Illuminating Primer, Victoria's Secret Airbrush FX, Boots Instant Matte, and plain old Aloe Vera Gel.

For good, affordable eyelid primers I like NYX Eyeshadow Base, E.L.F. Mineral Eyelid Primer (only $3!) and Etude Proof 10.

you can, however eye primer tends to be denser since you tend to pack more makeup around the eyes, and you want your shadows to look really pigmented. face primer is usually a lot lighter.

Yes, I use it as both sometimes and it does the same job.

i read online somewhere that yes, you can. every day i put it on my face as well as under my eyes and on my eyelids