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The New Zealand Railways Magazine, Volume 2, Issue 1 (April 21, 1927)

Sight Testing

page 18

Sight Testing.

The gradual introduction of the three light automatic signalling system into the New Zealand Railway service has drawn attention to the necessity of correct vision amongst the staff employed in connection with train running. The automatic light system displays all signals, both by day and night, with different coloured signal lights, and it has been proved that under the method in use, the light signal has a greater visibility, in daylight, than has the semaphore signal. This result is obtained by setting a strong light in a recess. It can be readily understood that safe working depends, in part, on the ability of members working under this system to correctly interpret the light signals displayed for their guidance. Investigation and careful comparisons by the Department of the practice in other Railway services has resulted in a standard examination being set for all employees in the Service.

The examination is conducted under two phases, the first being for visual acuity (which, in plain English, means eyesight), and the second for colour perception. In the visual acuity examination the test is for long distance sight, and varying standards are set, according to the responsibility of the members concerned. Each eye is tested separately and members are required to read clear type at a distance of twenty feet. The highest standard is required from the locomotive and signal box staffs, a degree lesser is allowed for the general traffic (including guards, porters, shunters and clerical traffic staffs), then a somewhat lesser standard is required from the remainder of the staff whose duties do not bring them into actual contact with train movements. The use of glasses is allowed when the members concerned do not have the actual handling of signals or are not engaged in train working duties. For instance, stationmasters (where signal boxes are in operation), traffic and maintenance foremen, storemen and platform workers are all allowed to wear glasses. Signalmen whose glasses have been tested by a medical officer and who are provided with two pairs of glasses are allowed to use them whilst engaged in their work. On the other hand members of the locomotive staff who are exposed to the effects of weather, steam, smoke and dust, are not permitted to use glasses, it being held that under these conditions the glasses would become a handicap rather than a help. The wearing of glasses too by members who are engaged in shunting duties would be a similar handicap because of the likelihood of the glasses becoming displaced in the running and jumping, inseparable from this class of work. It has been contended that railway work imposes a heavy strain on the eyesight. In consequence of this members suffer hardships through having to pass a fairly severe test. The contention, however, has not been borne out as a result of examinations. The older members of the service have been found to have retained their eyesight efficiency to a high standard, the number of failures amongst them being very few. This is probably due to the fact that candidates before being accepted for positions in the service are required to pass a rigid test. It can safely be said that, given freedom from accident and the absence of any constitutional weakness, the average member will continue to pass without difficulty the required tests throughout his railway career. It should be remembered that the visual acuity examination is for long distance sight only, and members should be careful not to strain their reading sight by neglecting to use glasses when such aid becomes necessary. The reading sight of the average person commences to deteriorate when he reaches the age of about forty years. It is advisable from this age upwards (indeed at the first indication of weakness) to give attention to the sight, and, if necessary, to resort to the assistance of glasses.

The second phase of the departmental examination is for colour perception. This side of the examination is not so easily understood, but is quite as important as the visual acuity examination. The average person possesses what is termed “correct” colour perception, and cannot quite understand how anyone can make mistakes in interpreting colours. Let it be clearly understood that many colour defective persons possess splendid eyesight and there is not necessarily any relationship between the two conditions.

Normal persons can distinguish the six different colours which go to form the rainbow, namely, red, orange, yellow, green, blue and violet. All the other colours—the names of which are legion—are combinations or shades of these six colours and the normal sighted, whilst not able to give names to all page 19 colours, can always distinguish one from another. The person of defective colour vision cannot distinguish the six primary colours, but such person can, according to the degree of his colour defectiveness, distinguish some of these colours. Some can see five colours, others four, others again three and two. The totally colour blind person can distinguish one only. To this last group all the world appears grey. Happily this is a rare condition. There are less than a hundred recorded cases of total colour blindness.

The object of the departmental sight testing examination is to ascertain the degree of sight defectiveness and to classify members accordingly. The systems adopted after careful investigation are those set by Professor Stilling of Leipzig University, Professor Ishihara of Tokio Univeristy, and Dr. Edridge Green an English authority. Stilling's and Ishihara's tests are known to the rank and file as the “Confetti” test—an apt name for everyday use. The principle is that a background resembling strewn confetti is formed in a certain shade and running through it in a related shade are letters or figures. Both background and letters are graded, that is, some of the dots are darker than others, though in all cases there is sufficient contrast to enable the normal sighted to read the letters or figures. The vision effectiveness or defectiveness of a person is proportionate to his success or failure to distinguish the letters or figures referred to. By this test the examiner is able to form an opinion of the extent of the sight defect of the individual concerned. But difficulty with the confetti test does not necessarily mean failure. There is a final test in which reliance is placed on Dr. Edridge Green's lantern. This lantern is designed so that lights can be exhibited under all conditions obtaining during ordinary railway working—the lights shown being similar to those in every day use in railway signalling.

Cadets in Railway Training School, Wellington.

Cadets in Railway Training School, Wellington.

The effect of distance is obtained by the reduction in the size of the aperture through which the light is shown, and lights can be reproduced similar to signal lights at any given distance. The test distance does not exceed an ordinary signal light at eight hundred yards. Conditions similar to rain, fog, smoke, etc., are obtained by the use of dulling glasses, due allowance being made in these cases for changes in the shades of the lights. In the lantern test the examiner has to exercise the utmost care in order to fully satisfy himself as to the colour vision of the member being examined. Although it is not pleasant to have to fail any member the safety margin must be maintained not only for public protection, but for the protection of the member himself. It is interesting to note that the number of failures for colour perception in the service has been found to be about equal to the percentage found by eminent authorities who have investigated this increasingly important question.