ASTIGMATISM

is a defect in vision due to the front of the eye not being of the right shape. A point must be focu ed as such on the back of the eye to be seen repent In order that this may occur the curvature of the eye in t horizontal plane must be the same as that in the vertical plane. When the two curvatures are unequal astigmatism is present. Points are then seen as lines unle the internal muscular mechanism of the eye is capable of correcting the ‘ error. Such correction commonly occurs, but it involves a: muscular strain that often induces headaches and bilious attacks, and when the health is ran down the correction is: incomplete and the sight blurred. The treatment consists in measuring the difference between the two curvatures and = then in ordering special gla es so made as to compensate for the error. All muscular strain within the eye is thus relieved, though the gla es may have to be worn a few daye before the cyc loses the habit of straining, hence at first [s. 333]