. A practical treatise on medical diagnosis for students and physicians . EXAMINATION OF THE EYE AND EAR. as these arc valuable and often necessary adjuncts in establishing thediagnosis of many obscure cases of cerebral disease. Central vision is tested by means of black letters printed on a whitetest-card, those devised by Snellen being usually employed on account ofthe admirable system upon which they are founded. The patient is seatedfive metres away from the card and, one eye being blindfolded, he is re-quested to read the lowest line of letters that he can distinguish. Ifthe vision tails
. A practical treatise on medical diagnosis for students and physicians . EXAMINATION OF THE EYE AND EAR. as these arc valuable and often necessary adjuncts in establishing thediagnosis of many obscure cases of cerebral disease. Central vision is tested by means of black letters printed on a whitetest-card, those devised by Snellen being usually employed on account ofthe admirable system upon which they are founded. The patient is seatedfive metres away from the card and, one eye being blindfolded, he is re-quested to read the lowest line of letters that he can distinguish. Ifthe vision tails to correspond to the standard, it is necessary to excludehypermetropia, myopia, and astigmatism by means of convex, concave,and cylindrical lenses before it can be definitely asserted that the visionis lowered as the result of disease. Peripheral vision, or the extent of space of which the eye is consciouswhen it is fixed on any given point, may be estimated in several ways; itis accomplished, however, most accurately by means of the perimeter. Fig. This instrument consists of an upright rest for the chin aud a semicir-cular arc or bar, graded in degrees, which revolves on a central pivot,and is capable of describing a hemisphere in space. The eye underexamination being directed straight ahead at the fixation-point, the felloweye being blindfolded, the test-object (consisting of a small square ofwhite paper) is brought from the periphery toward fixation. The patientis then asked to indicate the instant the object is perceived, and theexaminer marks the degree upon a chart provided for the purpose. If a HEMIANOPSIA-. 185 perimeter be not at hand, the field may be obtained fairly accuratelyas follows: The patient is seated opposite the surgeon with one eyebandaged. He is then directed to look at the corresponding eye ofthe examiner while the observers finger is slowly brought in from theperiphery toward the eye through the different meridians. In this waythe examiner can asc
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