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. 1920 Excerpt: ...Being Made at Thirteen Inches. We shall refer to this method as the concave-at-near procedure. The normal reading point is ordinarily about twelve to fifteen inches from the eyes; we shall take thirteen inches, equivalent dioptrically to 3' D., as a normal reading distance. A moment's consideration will convince the ...
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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. 1920 Excerpt: ...Being Made at Thirteen Inches. We shall refer to this method as the concave-at-near procedure. The normal reading point is ordinarily about twelve to fifteen inches from the eyes; we shall take thirteen inches, equivalent dioptrically to 3' D., as a normal reading distance. A moment's consideration will convince the reader that a very logical procedure in investigating the amplitude of accommodation would be to find its reserve at the reading point and to then add this quantity to the three diopters demanded while reading No. 2 Jaeger at thirteen inches. It should be accepted as a fundamental principle that any ocular function should be investigated under conditions of activity or quiescence which conform to the philosophy of the particular phase of its activity under consideration. The normal reading point is at a foot from the eyes; it is logical, therefore, to determine its reserve with respect to the point at which this reserve should hold. The thirteen inch or thirty-three centimeter point should be ordinarily chosen as the point at which the accommodative resources are to be investigated rather than a nearer or more remote point, for the reason that nature has ordained the establishment of a comfortable convergence point (leaving two-thirds to threefourths of the fusional convergence in reserve) and a normal distance of distinct vision at about a foot from the eyes. In passing, let it be stilted that we believe that the function of convergence, which normally remains constant in its strength, rather than accommodation, which becomes depleted with age, is the determining factor in the establishment of this normal reading or close work distance. The method is easily carried out. The test should be made monocularly and before each eye should be placed th...
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