The refraction of the eye; including a complete treatise on opthalmometry; a clinical text-book for students and practitioners . e. Nine months ago he had spherical glassesfitted on account of presbyopia, but they have been unsatis-factory. He consulted me first in February, 1893, when thefoil.)wing condition of affairs was found : — Ophthalmometer.—Shows no corneal astigmatism, that is. theimages of the mires neither overlap nor separate at any positionafter they have once been approximated, and the black linesdividing them into halves remain opposite and straight in allpositions. In such cas
The refraction of the eye; including a complete treatise on opthalmometry; a clinical text-book for students and practitioners . e. Nine months ago he had spherical glassesfitted on account of presbyopia, but they have been unsatis-factory. He consulted me first in February, 1893, when thefoil.)wing condition of affairs was found : — Ophthalmometer.—Shows no corneal astigmatism, that is. theimages of the mires neither overlap nor separate at any positionafter they have once been approximated, and the black linesdividing them into halves remain opposite and straight in allpositions. In such cases it is usual for the patient to have lenticular ILLUSTRATIVE CASES 57 astigmatism of aboul .50 1>. against the rule, that is to say, ifthe eye is hypermetropic that a plus cylindrical glass will beworn with its axis at 180°, or in that neighborhood, while ifmyopic a minus cylindrical glass will be worn at 90°, or inthat neighborhood. A and /> in Fig. -7 show the shape of the cornea and Lensrespectively, and focuses of the two chief meridians combined inthe present case. A shows both meridians of the cornea to. Fig. 27. have the same radius of curvature, therefore the cornea to bespherical in shape. It is emmetropic in refractive power inthis case. The lens (B, Fig. 27) is emmetropic in refractive power inthe horizontal meridian also, but in the vertical meridian it ishypermetropic by .50 D. As both the cornea and the lens are emmetropic in thehorizontal meridian, it allows the rays of light that pass throughthat meridian to focus exactly on the retina. The cornea isemmetropic in the vertical meridian also, but the lens is hyper-metropic .50 D., and consequently the rays of light that pass 58 THE REFRACTION OF THE EYE through that meridian focus behind the retina. It requires acylindrical glass of .50 D., axis 180°, to focus these rays oflight on the retina ; and a plus cylindrical glass worn with itsaxis at 180° shows the astigmatism to be against the
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