Skiascopy and its practical application to the study of refraction / by Edward Jackson, A.M.,M. D.

  • Jackson, Edward, 1856-1942.
Date:
1896
Catalogue details

Licence: Public Domain Mark

Credit: Skiascopy and its practical application to the study of refraction / by Edward Jackson, A.M.,M. D. Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

    40/122 (page 34)
    mately [when the observer has learned to appreciate its significance] the extent of the interval between the position of the observer and the point of reversal. If the movement be slow, the interval is large, perhaps several dioptres. If it be rapid, the interval is less. Upon these data of the direction and rapidity of the movement, the surgeon bases the next step of the test, the selection and placing of lenses before the eye. This being done, the test is repeated, the movement seen through the lens noted, both as to its direction and rapidity, and the distance of the observer from the patient, or the strength of the lens before the observed eye, varied in accordance therewith. This process is continued until the observer's eye reaches the point of reversal, or the point of reversal is brought by the lens to the observer's eye. But the test should not be regarded as complete until the movement has been repeatedly viewed both from within and from beyond the point of reversal, as well as from that point. Only by this precaution of observing from a slightly greater and a slightly less distance, or with a slightly stronger or slightly weaker lens than that which brings the point of reversal to the surgeon's eye, can the certainty of a correct result be assured.