A simple clinical method for measuring the diameter of the pupil / by Tom A. Williams.

  • Williams, Tom A. (Tom Alfred), 1870-
Date:
1910
Catalogue details

Licence: In copyright

Credit: A simple clinical method for measuring the diameter of the pupil / by Tom A. Williams. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Showing the distance in millimeters of the perforations in the test card. The pupil is normally not larger than the distance between the dots in the space marked 4. Inequal- ity between the two pupils may be ascertained by making two holes at a distance exactly corresponding to the diam- eter of one pupil and then ascertaining whether the circles exactly touch when the holes are placed before the other pupil. But this well-known method gives only the tem- porary pupil diameter, which is very variable in dif- ferent persons. For purposes of absolute compari- son, it is necessary to combine it with a standard state of pupillary adaptation. Now, it is known that although it requires two hours in the dark for maxi- mal dilatation to occur, yet a convenient, practical, very extensive adaptation to dark occurs at the end of two minutes and is almost maximal in twenty. Upon reexposure to light the pupil contracts in pro- portion to the logarithm of intensity of the light to which it is exposed. But Schirmer2 has found that there is practically no variation in the amount of contraction within the very wide range of one hundred and eleven hundred millimeter-candles, and that in normal individuals the pupil measures between three and four milli- meters after maximal adaptation to dark. Char- pentier3 found increased sensitiveness even greater than did Aubert after pupillary adaptation to dark- ness ; but the clinical importance of the facts does not warrant their discussion in this place. Hence if the patient to be examined is placed in the dark room for two minutes, and then placed so that his eye is exposed to a light between one hun- dred and eleven hundred candle-power, a standard stimulus is attained uniform enough for the prac- 2