Handbook of ophthalmology . opiadepends upon a flattening of the cornea must be regarded as fullydisproved. So, too, contrary to the old idea that myopia depended uponexcessive curvature of the cornea, it has been found that with thatcondition of refraction the radius of curvature is generally greaterthan in emmetroj^ia; in fact, that it increases with the degree ofthe myopia. The reason for this is, that in myopia not only thevisual axis, but all the diameters of the eye, are increased. In hypermetropia, also, Donders found the cornea on an averageless curved than in emmetropia; still, he dis
Handbook of ophthalmology . opiadepends upon a flattening of the cornea must be regarded as fullydisproved. So, too, contrary to the old idea that myopia depended uponexcessive curvature of the cornea, it has been found that with thatcondition of refraction the radius of curvature is generally greaterthan in emmetroj^ia; in fact, that it increases with the degree ofthe myopia. The reason for this is, that in myopia not only thevisual axis, but all the diameters of the eye, are increased. In hypermetropia, also, Donders found the cornea on an averageless curved than in emmetropia; still, he discovered no relationbetween the degree of the hypermetropia and the length of theradius of curvature. Numerous measurements have proved that the different me-ridians of the cornea possess radii of different lengths, and thatthe vertical meridian generally has the greatest curvature. Thecurvature of each individual meridian is nearly elliptical. Under normal relations the line of vision always deviates inward * L. c, pag. 122 THE OPHTHALMOMETER. from the centre of the cornea. The angle which it forms with theaxis of the cornea is called the angle oc. Donders* measuredthe size of this angle in the following manner. A flame wasplaced vertically and immediately over the ophthalmometer, andits image reflected in the cornea was observed front of the eye under examination was placed a horizontalgraduated arc, with its centre opposite the centre of rotation of theeye. Upon this was placed a movable object, which served as a fixation-point for the eye under exam-Ficj- 29. ination, and made it possible so to direct 1S5>?d^fP^^ it that the image of the flame should be reflected exactly from the centre of thecornea. This was the case when, uponrevolving the glass plates of the oph-thalmometer, the double images of thecorneal reflex reached simultaneously corl*^erexin order rlee Ihe ^^ ^Oth sidcS the bordcr of the doubleeye under examination with suffi- images
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