A method of determining the refractive state of the eye based on the criterion of sharpness of an image. The observer determines the position at which a point source appears in the best focus, while the eye is unaccommodated: this indicates the far point of the eye. If the eye is astigmatic, the point source will appear as a line or streak when at the far point of each principal meridian. The distance between the two foci corresponds to the cylinder correction and the slant of the streaks from the horizontal or vertical indicates the axis of the astigmatism. See refractive error; stigmatoscope.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann