Also known as a chalazion, a meibomian cyst is a blocked up, inflamed meibomian gland. There are lots of these tiny glands just under the inner surface of the eyelid that make an oily fluid forming part of the tear film. If the gland gets blocked the oil cannot escape and it may expand into a fluid-filled swelling (cyst). If it is causing problems and does not settle on its own, it can be removed with a small operation.
A stye appears along the edge of the eyelid due to infection in the root of an eyelash. It may start off as a small red lump but, as it develops into a collection of pus (a little abscess), it looks like a yellowish spot on the edge of the eyelid.