A chalazion is an inflammation or blockage of the deep oil glands within the eyelid that develops into a small hard mass.
A chalazion first appears as a firm lump under the skin but is usually not painful.
Sometimes, a chalazion develops after a sty has healed.
On rare occasions, if a chalazion becomes quite big, it can press on the cornea.
If the chalazion is on the upper eye lid, it can produce various vision problems including astigmatism, a distortion of the lens that causes fuzzy vision.