The refraction of the eye : including a complete treatise on opthalmometry : a clinical text-book for students and practitioners / by A. Edward Davis.

Date:: 1900

Credit: The refraction of the eye : including a complete treatise on opthalmometry : a clinical text-book for students and practitioners / by A. Edward Davis. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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$1. Simple hypermetropic astigmatism with the rule.— Figure No. 9 shows the vertical and horizontal sections of an eye with such an error of refraction. It is seen by this diagram that the vertical meridian is emmetropic and allows the rays of light to focus on the retina, and is more curved than the horizontal meridian which is flat and allows the rays of light to focus back of the retina. Therefore, according to our definition of astig- matism with the rule, this must be a case of it, for the vertical meridian is more curved than the horizontal. 2. Compound hypermetropic astigmatism with the rule. — In such a case the vertical meridian is flat and allows the rays of light to focus back of the retina, but it is not as flat as the horizontal meridian which allows the rays to focus still farther behind the retina. Here again the vertical meridian is more curved than the horizontal, and, of course, the astigmatism is with the rule, though it is compound hypermetropic. 3. Simple myopic astigmatism with the ride. — Here the ver- tical meridian is myopic, causing the rays of light to focus in front of the retina, and is more curved than the horizontal meridian which is emmetropic, and allows the rays to focus on$