Ocular refraction and the shadow test . nder certain conditions; but, hemay, and doubtless will ask—How is one to know, when one observesan eye with the retinoscope, whether it is emmetropic, myopic orhypermetropic?—The answer is; the appearance of the luminouspupil varies according to the diflterent conditions of refraction. Thus far the theory of retinoscopy has been explained, the nextstep will be to take up acliialpractice and -norking conditions The study of retinoscopy has brought into use a simple devicecalled the model eye, which is a most valuable aid to the student, who RETINOSCOTY.
Ocular refraction and the shadow test . nder certain conditions; but, hemay, and doubtless will ask—How is one to know, when one observesan eye with the retinoscope, whether it is emmetropic, myopic orhypermetropic?—The answer is; the appearance of the luminouspupil varies according to the diflterent conditions of refraction. Thus far the theory of retinoscopy has been explained, the nextstep will be to take up acliialpractice and -norking conditions The study of retinoscopy has brought into use a simple devicecalled the model eye, which is a most valuable aid to the student, who RETINOSCOTY. 165 may practice upon it by the hour without its entering any protest offatigue. A description of it in the inventors own words will is shown in figure 134. The eye is made of two cylinders of cardboard, one slightlysmaller than its fellow, to permit slipping easily into the other. Bothcylinders are well blackened inside. The smaller cylinder is closedat one end, and on its inner surface is placed a colored lithograph of. Figure 134. Model eye for the study of retinoscopy. the normal eye ground. The larger cylinder is also closed at oneend, for a central round opening, ten millimeters in diameter,which is occupied by a plus twenty dioptre lens. On the side of the small cylinder is an which recordsemmetropia, and the amount of myopia and hypermetropia accordingas it is pushed into or drawn out of the large cylinder. In other words, the model eye can be set to represent emme-tropia, myopia to six diopters or less, and hypermetropia to sixdiopters or less; by merely sliding the two cylinders so as to changethe axial length of the eye. By placing a cylinder lens from the testcase before the model eye, an astigmatic condition may be createdand studied. These cardboard model eyes are inexpensive and the student isadvised to procure four of them for the purpose of practice. Nearlyall knowledge is drawn from comparisons, and in the study of retin-oscopy th
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