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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1900 Excerpt: ...2A at the meter-plane, and therefore a vertical diplopia of 12 centimeters at 6 meters, which amounts to 20 meters at one kilometer, or, approximately, in round numbers, 66 feet at a distance of 3,281 feet. This shows that the vertical adjustment of the lens-centers before the eyes should receive fully as much attention as their horizontal distance apart. While emmetropes may have one eye much higher than the other, and still enjoy comfortable binocular vision, yet the same discrepancy in ocular elevation in an ametrope whose glasses have been fitted with their optical centers on the same horizontal plane, will produce great discomfort on account of one of the lenses projecting its image eccentrically to the macula of at least one eye. Measurement by the phorometer will in this instance reveal an apparent hyperphoria, which in reality does not exist as a muscular anomaly. Inversely, in making Dr. Stevens, test for hyperphoria, in emmetropia for instance, supposing a means to be devised to enable the patient to exactly indicate the distance between the images which he sees at a 6-meter distance. Admitting, by way of illustration, that he has decided them to be 6 centimeters apart, vertically, which, being equivalent to leTM at 1 meter distance, will lead us at once to decide that a prism of 1A, properly placed before the eye, will correct his manifest hyperphoria. The same patient would have to struggle with a vertical diplopia amounting to 37 ' a a reading distance of 33Jcm, being quite sufficient to cause consecutive lines of small type to appear intermingled with each other. Functional Nervous Diseases, by George T. Stevens, M.D., Ph.D., New York, 1887, page 194. Shortly after this paper was first published, the author devised the following simple a...

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