PRACTICAL EXERCISES 



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of a metre, there is in this case myopia amounting to one diopter. 

 If, however, the light area moves in the same direction as the 

 rotation of the concave mirror, the far-point of the observed eye 



-27 



14 



46 



FIG. 443. GENEVA RETINOSCOPE AND OPHTHALMOSCOPE. 



A, frame of instrument ; B, retinoscope attachment ; C, ophthalmoscope 

 attachment ; D, base ; i, mirror handle ;]2, clip to hold the proper lens to correct 

 the abnormality of refraction of observer or patient when viewing the retina with 

 the ophthalmoscope ; 3, scale indicating the meridian of handle and pointer ; 4, 

 ring in which mirror cup rotates ;]6, mirror ; 7, mirror spring for reflecting the light 

 to a given point ; 8, screws for adjusting mirror ; 9, screw for holding light and 

 ring 4 in position ; 10, handle for swinging A from side to side 513, opening in iris 

 diaphragm, controlled by handle 14 ; 15, lamp hood ; 17, knurled handle for rotating 

 disc containing the full diopter lenses ; 18, handle for rotating the disc containing 

 the fractional lenses (white numbers indicate plus lenses, and red minus lenses) ; 

 20, opening through which observer looks when adjusting the retinoscope to the 

 patient's eye ; 21, pinion for advancing or retracting instrument ; 24, bracket 

 ring of retinoscope attachment B, which is slipped over ring 25 when putting 

 retinoscope attachment into place ; 28, clips for ' fogging ' lenses through which 

 the patient looks to relax accommodation ; 29, opening through which the pupil 

 is viewed in retinoscopy ; 30, opening containing clip in which extra lenses may 

 be inserted when required, or the defect is over 8 diopters ; 32, patient's eye- 

 cup ; 33, ring of ophthalmoscope attachment C, which telescopes over 25 ; 

 34, ophthalmoscope tube ; 35, binding-screw which holds the instrument in a 

 fixed position when retinoscope is being used ; 37, rack to raise and lower the 

 instrument ; 40, handle controlling height of chin-rest 44 ; 46, forehead-rest. 



lies between the observer and the observed eye, so that the myopia 

 amounts to more than one diopter. The precise degree of myopia 

 can be estimated by interposing biconcave lenses of different strength 

 until the far-point is made just i metre. 



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