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.

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    still closer to the patient until this inverted movement ceases. He will then be near the point of reversal for the meridian in which the inverted movement was before noticed, and will be able to see in the other meridian an erect movement. Such a lens is now to be chosen and placed before the eye as will bring this point of reversal for the more myopic meridian—the point of reversal from which an erect move- ment is seen in the other meridian—to a convenient distance from the eye. The surgeon's eye is placed as nearly as pos- sible at this point of reversal. Then the original source of light [which has up to this stage of the test accompanied the mirror in its movements to or from the patient's eye] is pushed away from the mirror, and while it is pushed away, the mirror is rotated and the light area in the pupil watched. This light area will now be seen to assume the band-like appearance characteristic of astigmatism. At a certain distance this band-like appearance will be most distinct. With the source of light nearer the mirror or farther from the mirror, it will be less characteristic. The distance of the light from the mirror at which the band becomes most distinct is the distance between the two points of reversal. The surgeon's eye (with the mirror) is now at the point of reversal for the more myopic meridian, and the immediate source of light is at the point of rever- sal for the less myopic meridian. (See page 48.) With the light in this position, the direction of the band is to be carefully studied and noted as the direction of one of the principal meridians of astigmatism. It is the direction of the axis of the convex cylinder that will cor- rect the astigmatism. The other principal meridian will, of course, be perpendicular to this. Having now fixed the direction of the principal me- ridians of astigmatism, the surgeon should again bring the original source of light as near to the mirror as possible,