. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, rry lor-gnettes, which they hold up in front of the near correctionto improve distant vision for a few minutes, or, wearing thedistance correction, can use a plus lens in the lorgnettes fornear vision. 9. Cases of monocular aphakia where the vision in thefellow-eye is very defective can wear reversible frames, onelens for distance and the other for near,—that is to say, aframe which has a free joint at the temples,—and in this waythey avoid bifocals, and can change the
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, rry lor-gnettes, which they hold up in front of the near correctionto improve distant vision for a few minutes, or, wearing thedistance correction, can use a plus lens in the lorgnettes fornear vision. 9. Cases of monocular aphakia where the vision in thefellow-eye is very defective can wear reversible frames, onelens for distance and the other for near,—that is to say, aframe which has a free joint at the temples,—and in this waythey avoid bifocals, and can change the distance for the near correction by turningthe temple-pieces. In some cases of apha-kia where the lens is verypowerful, a bifocal segmentcan sometimes be dis-pensed with, if the patienthas a long nose, by slid-ing the lens down fromthe eye and then holding the reading matter at the conju-gate focus. A toric lens (Fig. 181) is very acceptable inoccasional instances, as it reduces somewhat the weight andthickness of the lens, and also enlarges the field of toric {torcinc or toriqin, twisted) lens is one which. Copyright, 1S86, by Chas. P. Prentice. Fig. 181. BIFOCALS. 279 has, combined in one surface, the optic effects of a sphero-C}lindric lens, or two cyUnders of different streni^th at ri^^ditangles to each other. Unfortunately, this kind of a lens isquite expensive. General Considerations.—Before prescribing any pairof glasses, the patient should have the opportunity to wearthe correction in the office for a short time, that he maystudy its effect; this is especially necessary (i) when theglasses are strong ones ; (2) when there is monocular as-tigmatism ; (3) when one lens is much stronger than theother (anisometropia) ; (4) when the astigmatism is asym-metric ; or (5) when there is a strabismus, etc. The patientloses confidence (and the surgeon is not made happ)^) whenthe patient returns with his glasses in his hands and statesthat he can not wear them—that
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