Skiascopy and its practical application to the study of refraction . Fig. 7. Fig. 8. In estimating astigmatism by skiascopy, two distinctthings are to be done, which require different arrangementsof the source of light. The first is to determine accuratelythe direction of the principal meridians by bringing outmost distinctly this band-like appearance in the pupil, in-dicating the direction of one of these principal meridians ;the other being always, for regular astigmatism, at rightangles thereto. The second thing to be done is to measureaccurately the refraction in each of these principal me
Skiascopy and its practical application to the study of refraction . Fig. 7. Fig. 8. In estimating astigmatism by skiascopy, two distinctthings are to be done, which require different arrangementsof the source of light. The first is to determine accuratelythe direction of the principal meridians by bringing outmost distinctly this band-like appearance in the pupil, in-dicating the direction of one of these principal meridians ;the other being always, for regular astigmatism, at rightangles thereto. The second thing to be done is to measureaccurately the refraction in each of these principal merid-ians. The test proceeds at first as for myopia or hyperopia ina non-astigmatic eye, until a point of reversal is it is discovered that this point of reversal is only forthe movement of light and shadow in one direction, anddoes not hold for movements at right angles to that direc-tion. The observer has now brought his eye to one pointof reversal where the band-like appearance can be best per-ceived. But, as he has been working with the originalsourc
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectretinos, bookyear1896
