A sty is an infection of one of the oil glands or eyelash follicles on the eyelid margin. The medical term for a sty is hordeolum. They are often very tender to the touch and can be very red and swollen. The treatment for a sty is the application of a warm compress to open the gland and massage to promote drainage. Some patients require antibiotics and possible surgical drainage in severe cases. Another similar condition is called a chalazion, which is a clogged gland but does not involve infection. They tend to be a non-tender bump in the lid and the treatment is the same. Contact an optometrist or ophthalmologist for more information.