Color blindness : remarks / by B. Joy Jeffries at the twenty-ninth annual meeting of the board of the supervising inspectors of steam vessels.

  • Jeffries, B. Joy, 1853-
Date:
[1881]
Catalogue details

Licence: Public Domain Mark

Credit: Color blindness : remarks / by B. Joy Jeffries at the twenty-ninth annual meeting of the board of the supervising inspectors of steam vessels. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    usual condition and relative brightness, by which alone they decide^ then we can realize that, however well they may apparently guess at colored signal-lights close-to, they are most dangerous on the look-out, or in command, or at the wheel. This use of London-smoked glass to test the color-blind must, of course, be thoroughly understood, and the X)rinciple of its application. When thus understandingly employed, it is a great help to the expert in proving the defect to the interested laity. But now to reply to a member of the board, who says: You have shown us all these difiterent tests by various experts, each one of whom probably thinks his is the best; how are we to decide as to their rela- tive merits ? &c. The several ways of examining which have been exhibited are all control tests, to fortify the result obtained by the first and simplest method, namely, Holmgren's worsteds. There is no question of one being better than the other. Except for determining the amount of color-blindness, they are not needed. Wherever they show color- blindness, the Holmgren test will do it in infinitely less time. The sev- eral Government Departments do not require them, as they have not yet decided on the standard amount of color perception requisite. This renders it all the more necessary that the examiner should be very familiar with the worsted-test and have thoroughly mastered it, which even Prof. Holmgren says cannot be done without patient, intelligent study and x)ractical experience. It has been greatly to the credit of the medical officers of the Marine-Hosx)ital Service, and proof of the value of the method, that they have succeeded so well with it. This is shown in the annual report of the Sui)ervising Surgeon-General. Inability on the part of the laity to conceive it possible that such a seemingly common-place test as the worsteds really at once pointed out the dangerous i)ilot or engineer, and the necessity of deciding the amount of color-blindness, have called for these additional quantitative and control tests. But the examiner must understand them thoroughly, and be competent to explain them in exhibiting the defect of the color- blind he is testing by them. Visual acuteness, or the power of form perception, is tested by the same means all over the world, namely, the ability to read letters or distinguish forms of certain sizes at certain distances under the same circumstances of illumination. Normal visual poiver has been decided by the average of hundreds of thousands of normal eyes. It is to be able to read these test-letters at twenty feet; of course the eye, if neces- sary, to be fitted with the glasses it may need from being near-sighted, over-sighted, or astigmatic, &c. The standard of normal vision is un- doubtedly rather too low than too high. In the I^avy and Army a definite standard is required in recruits. No definite one is ordered for pilots, as certainly ought to be. The examination of the eyes and the testing the vision is, by the Treasury orders, left to the medical officer, as he alone can, when the vision is defective, examine the interior of the eye and determine the cause of such defect, and w^hether, as with cataract, &c., it is progressive. So, also, he alone can say whether there is granular lids, the results of specific or other disease, liable to cause future trouble, and so on. It is only he, and he only when he under- stands, who can detect the cause of failing vision for distance, which comes with increasing years, and can only be remedied with glasses. This cause is the very common defect known as over-sightedness, the eyeball being just the reverse from near-sightedness, too short. This de-
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