astigmatism

/əˌstɪgməˈtɪzəm/

/əˈstɪgmətɪzəm/

The eye has a cornea — a clear, curved layer that protects it. If the cornea's shape is irregular, astigmatism results. People who have astigmatism see images as distorted, so they need to wear glasses or contact lenses.

Sometimes people mistakenly say, "One of my eyes has a stigmatism." But the a in astigmatism is important to its meaning. The prefix a- means "without." Stigma is Greek for "point," so an eye that is "without point" is one that doesn't allow light rays to meet at a single point or focus. Since astigmatism is a condition, you don't need the article an before it: "My eye has astigmatism," not "My eye has an astigmatism."

Definitions of astigmatism

1. noun

   (ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea; common in nearsighted people
   synonyms: astigmia

   types:

   keratectasia

   abnormal bulging of the cornea of the eye

   keratoconus

   abnormal cone-shaped protrusion of the cornea of the eye; can be treated by epikeratophakia

   type of:

   ametropia

   (ophthalmology) faulty refraction of light rays in the eye as in astigmatism or myopia
2. noun

   (optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point
   synonyms: astigmia

   antonyms:

   stigmatism

   (optics) condition of an optical system (as a lens) in which light rays from a single point converge in a single focal point

   type of:

   condition, status

   a state at a particular time