Hey Gazz, not as much work as you might imagine, you could lower the topo on the head some to make it easier, otherwise you could select some polys where the eyes are currently do an inner extrude, then fit circle command, then delete the selected polys and shape to your liking. which will essentially give you some nice oval/circular holes where the eyes are currently, delete the old eyes, loop select and extrude to bring out a ring of new polys to start forming your new eye lids, extrude a couple more times and shape as necessary. should end up with something like whats pictured below, you can add/remove loops around the eyes as necessary for a clean deformation. topo along these lines should be good, might need another loop or 2 around the base between the eye and the nose in the event of it distorting the area where the nose attaches near the inner eye, hope this helps some , V
p.s you can also add some more diagonal loops near the corners of the eyes if you want to sharpen them up a little, more like your existing eye shape.