astigmatism

/æs'tigmətizm/

Thân thiện

A person with astigmatism sees a blurry street sign at night.

Definition

1. Noun:
   • (Optics): A defect in an optical system (such as a lens or mirror) or in the eye where light rays from a single point do not converge into a single, sharp focal point, resulting in a blurred or distorted image.
   • (Ophthalmology): A common vision condition (refractive error) caused by an irregular curvature of the eye's cornea or lens. This irregular shape prevents light from focusing properly on the retina, leading to blurred or distorted vision at all distances. It often occurs alongside nearsightedness (myopia) or farsightedness (hyperopia).

Usage Examples

• Noun:
  • The new glasses corrected her astigmatism, making street signs much clearer.
  • The telescope's mirror had a slight astigmatism, which blurred the image of the planet.
  • An eye exam can diagnose astigmatism and determine the correct prescription for contact lenses.

Advanced Usage

• "To have astigmatism": To be affected by this vision condition.
  • Many people have a minor degree of astigmatism without realizing it.
• "Corrected for astigmatism": Describing lenses designed to compensate for this defect.
  • These toric contact lenses are specifically corrected for astigmatism.

Variants and Related Words

• Astigmatic (adj): Having or relating to astigmatism.
  • An astigmatic eye requires a special lens prescription.
• Astigmatically (adv): In an astigmatic manner.
• Stigmatism (n): The condition of having a point focus (the opposite of astigmatism, often used in contrast).

Synonyms

• Visual distortion (general term for the effect).
• Refractive error (the broader category of vision problems including astigmatism, myopia, and hyperopia).

Related Phrases

(Note: 'Astigmatism' itself is not typically part of phrasal verbs or idioms, but it is used in common medical/optical phrases.) - "Rule out astigmatism": To perform tests to determine if astigmatism is not present. - The optometrist needed to rule out astigmatism as a cause of the headaches. - "Compound astigmatism": Astigmatism combined with another refractive error like myopia or hyperopia.

Học thuật

Noun

1. (optics) defect in an optical system in which light rays from a single point fail to converge in a single focal point
2. (ophthalmology) impaired eyesight resulting usually from irregular conformation of the cornea; common in nearsighted people

Từ đồng nghĩa

• astigmia