. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, letters. Toavoid reflection, this card should behung at an angle. For aliens who do not know theEnglish letters, and for illiterates, aspecial card has been made, known asthe illiterate or dummy card, withcharacters consisting of lines shaped like the capital letter \\, and made to conform to the fivc-niinute angle. As these letters are warioush placed, thepatient is asked to tell, or indicate with his finger or fingers, -000 -M X Y V ?fl a a H M -T s o o A n • Y V T 3
. Refraction and how to refract : including sections on optics, retinoscopy, the fitting of spectacles and eye-glasses, letters. Toavoid reflection, this card should behung at an angle. For aliens who do not know theEnglish letters, and for illiterates, aspecial card has been made, known asthe illiterate or dummy card, withcharacters consisting of lines shaped like the capital letter \\, and made to conform to the fivc-niinute angle. As these letters are warioush placed, thepatient is asked to tell, or indicate with his finger or fingers, -000 -M X Y V ?fl a a H M -T s o o A n • Y V T 3 S X X Fic. 70.—Four Min-ute Letters of Wallace. Thiscard is constructed]5rincipally for re-flection purposes. u 3 LU E UJ 3 E 3 uj m ui 3 E m m ui n E Ul 3 E Fig. 72. METHOD OF PROCEDURE. 75 the direction in which the prongs of the E point: up,down, to the right or left. This ilHterate card (see ) is much to be preferred to the German, Hebrew, andfigure cards occasionally displayed in clinics. Selection of Test-cards.—The surgeon should haveseveral of these in duplicate with the order of the letters. Fig. 71.—Goulds Test-letters. Gothic letters in white on black cards. changed (Figs. 67, 71), as patients not infrequently and un-intentionally commit them to memory. Care should beexercised in the selection of test-cards, to see that eachletter on the card measures up to the standard square offive minutes, as many of the As and Rs and Ns, etc., onthe old cards as seen in the shops measure six and so\enminutes horizontally. It is a matter of choice with the 76 REFRACTION AND HOW TO REFRACT. surgeon whether to use test-cards with the block or Gothicletters. It is well to have both. Method of Procedure.—The test-card should be hungon the wall with its ^ line five or six inches below thelevel of the patients eyes, and illuminated by means ofreflected artificial light. This is always a certain quantity,whereas daylight is too variable and not to be dependedupon. T
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