A defect of the cornea or lens of the eye that causes blurred vision.
A condition that occurs because the cornea (outer lens of the eye) is not the correct spherical shape. Light rays from an object do not focus on the retina; they focus in front of or behind the retina, so the object appears blurred.
A defect of the refractive surface of the eye that distorts light rays so that they cannot focus on a single point on the retina.
Defective vision caused by change in curvature of cornea and lens.
A condition in which the eye cannot focus vertical and horizontal lines simultaneously, leading to blurring of vision.
Uneven curve of the cornea or lens.
A refractive anomaly due to unequal refraction of the incident light by the dioptric system of the eye, in different meridians.
Blurring or distortion of vision from a misshapen cornea in the eye.
Defect in vision in which the light rays cannot be focused properly on the retina because of abnormal curvature of the cornea or lens of the eye; corrective lenses improve vision.
A defect in vision caused by uneven curvature of the eye’s clear outer covering (cornea). The normal cornea is round, curving equally from top to bottom and side to side. In astigmatism, the cornea curves more in one direction than the other, making it asymmetrical. Astigmatism is usually present at birth and often increases through childhood. A minor degree of astigmatism is very common and considered normal and often requires no correction. More pronounced astigmatism changes little during school years. It can lead to blurred near and distance vision. Glasses or contact lenses specially designed to counteract the astigmatism are used to correct the condition; the correction provided by glasses or contact lenses for greater degrees of astigmatism can lead to tilting and distortion effects. Astigmatism can occur with other vision defects such as nearsightedness or farsightedness.
An error of refraction in the eye due to the cornea (the clear membrane in front of the eye) being unequally curved in different directions, so that rays of light in different meridians cannot be brought together to a focus on the retina. The curvature, instead of being globular, is egg-shaped, being longer in one axis than the other. The condition causes objects to seem distorted and out of place, a ball for instance looking like an egg; a circle like an ellipse. The condition is remedied by suitable spectacles of which one surface forms part of a cylinder. A hard contact lens may be fitted to achieve an evenly curved surface. Astigmatism may be caused by any disease that affects the shape of the cornea — for example, a meibomian cyst (a swollen sebaceous gland in the eyelid) may press on the cornea and distort it.
A form of ametropia in which the refraction of a ray of light is spread over a diffuse area rather than sharply focused on the retina. It is due to differences in the curvature in various meridians of the cornea and lens of the eye. The exact cause is unknown. Some types show a familial pattern.