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 to a focus together on the retina. The curvature, instead of being globular, is egg-shaped, 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.
Article Categories:Medical Dictionary