. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. nterior surface of thecornea. This bobbin is, by moving the frame out from the eye, un-wound until the vertical wires are seen with perfect accuracy. It is,indeed, possible to determine by means of such wires with sufficientaccuracy whether they are exactly seen, as by a slight deviation the mar-gins lose their sharp outlines, and more of these lines appear. Thepersons examined for the most part state this very easily. The readingof print, capable of being distinguished at given d
. On the anomalies of accommodation and refraction of the eye, witha preliminary essay on physiological dioptrics. nterior surface of thecornea. This bobbin is, by moving the frame out from the eye, un-wound until the vertical wires are seen with perfect accuracy. It is,indeed, possible to determine by means of such wires with sufficientaccuracy whether they are exactly seen, as by a slight deviation the mar-gins lose their sharp outlines, and more of these lines appear. Thepersons examined for the most part state this very easily. The readingof print, capable of being distinguished at given distances in due ac-commodation and by a sharp eye, may be used to control the result. Most optometers are based upon the principle of the well-knownexperiment of Scheiner: through two openings or slits, placed closerto one another than the diameter of the pupil, the object, forexample a wire, is seen, and this appears double if the eye is notaccurately adjusted to this distance. If we now cause any one to 3 34 RANGE OF ACCOMMODATION. look into such an optometer and to determine when he sees the wire Fiff. single, we shall in general obtain a distance to which the personeasily accommodates his vision, but this distance will not correspondto either the nearest or the farthest point. This is looked upon asthe mean distance of distinct vision. But to this we must not attachtoo much importance, for such a mean distance does not exist, or atleast it has a very wide range; this appears when a number ofdeterminations are made, for example with Stampfers optometer:the same person never obtains, even under the same circumstances,similar results, and where circumstances differ, the results vary verymuch. Only when a person has learned to control his power ofaccommodation, and can voluntarily bring it into the condition of thehighest action and of perfect relaxation, can we with such optometerssuccessively determine his farthest and his nearest point of distinctvision. But such volunt
Size: 1574px × 1588px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, bookidonanomalieso, bookyear1864
