. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, the horizontal meridian, tiierewould be seen a band of light extending across the pupilon axis 90 degrees. Then, substituting -( S. for S.,all movement will cease in the horizontal meridian,a -|-4-50 S. neutralizing the horizontal meridian. Thedifference between these two spheres is i D., which is theamount of the astigmatism. In neutralizing astigmatismthe writer advises using spheres, and after each meridian i68 REFRACTION AND HOW TO REFRACT. has been ref
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, the horizontal meridian, tiierewould be seen a band of light extending across the pupilon axis 90 degrees. Then, substituting -( S. for S.,all movement will cease in the horizontal meridian,a -|-4-50 S. neutralizing the horizontal meridian. Thedifference between these two spheres is i D., which is theamount of the astigmatism. In neutralizing astigmatismthe writer advises using spheres, and after each meridian i68 REFRACTION AND HOW TO REFRACT. has been refracted, to make the cyHndric correction, andprove it, if so desired. Axonometer.—To find the exact axis subtended by theband of hy;ht while studying the retinal illumination, whenthe meridian of least ametropia has been corrected, thewriter has suggested a small instrument, which, for want ofa better name, he has called an axonometer. This is ablack metal disc, with a milled edge, i ^^ mm. in thickness,of the diameter of the ordinary trial-lens, and mounted ina cell of the trial-set. It has a central round opening, 12. Fic. 148. mm. in diameter—the diameter of the average cornea at itsbase. Two heavy white lines, one on each side, pass fromthe circumference across to the central opening, bisectingthe disc. To use the , place it in the frontopening of the trial-frame, and with the patient seated erectand frame accurately adjusted, so that the cornea of the eyeto be refracted occupies the central opening. As soon asthat lens is found which corrects the meridian of leastametropia, and the band of light appears distinct, turn the KKTINOSCOPV. 169 axonomcter slowly until the two heavy white lines accu-rately coincide, or appear to make one continuous line withthe band of light. (See Fig. 148.) The degree mark on the trial-frame to which the arrow-head at the end of the white line then points is the exactaxis for the cylinder. Application of Retinoscopy in Mixed Astigm
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