EYESIGHT TESTS

Evening Star, Issue 23695, 1 October 1940, Page 3

EYESIGHT TESTS

CHECKING UP ON COLOUR BLINDNESS INFALLIBLE SYSTEM HOW EMPLOYED NO DECEPTION—EXCEPT IN WHAT IS SEEN Colour vision tests now conducted when men are being medically exam- . ined preparatory to joining tho Army reveal conclusively deficiencies of the sight where colour registrations are concerned. The method employed is a scientific one showing that a candidate , actually sees the correct colours, and it l is possible to declare without fear of contradiction that a man is totally colour blind or is blind only in regard to one of the primary colours. Actually the method is not new, and it has been made use of for a year or two when testing recruits for specialised tasks wherein an accurate appreciation of colours is most essential. It has attracted some attention of late .because of the number of men who have had their colour sense tested in Dunedin since tho war broke out. The method is one satisfactorily evolved, by Dr Sliinobu Ishihara, a colonel in the Imperial Japanese Army Medical Corps and a professor of opthalmology at the Imperial University of Tokio. NOW YOU SEE IT—NOW YOU DON’T. When being tested the candidate is confronted with a number of circles in which are bold numerals composed of 1 coloured dots of varying sizes set I against a background of similar dots) slightly differently coloured. The variations of colours used are such that a colour-blind person or a partially colour-blind person is confused so that ho either cannot see the numerals or reads them wrongly, according to the degree of deficiency. A ‘ Star ’ reporter examining tho method passed the tests with full marks, but through lenses he' was given an indication of how the circles would appear to a colour-blind person. It was surprising I to discover how many of the numerals were completely “ blacked out,” while others, in no way apparent to the naked eye, suddenly came into being. In other circles the candidate is supposed to follow a line from one marked spot to another. A normal person could do so in one circle, but not in the other, while tho reverse applied to a person affected by colour blindness. This test is claimed to be infallible, proving definitely the ability of the eye to register colour correctly, and enabling an assured classification of normal, safe deficiency, and unsafe deficiency sight. Unsafe deficiency refers to the extreme degree of colour blindness in which it is impossible for a person to define the colours of signals or any other association where the use of coloured lights, Hags, or symbols is of paramount importance. Colour blindness, other than the deficiency it infers, does not necessarily mean that a person affected has poor eyesight. Indeed, it has more often than not been proved that in every other direction a colour-blind person’s sight might be superior to that of a normal colour registering vision. The extent of colour blindness amongst males is set down by Dr Ishihara as 5 per cent., and although it has not been possible to obtain exact figures locally, it is thought that the same percentage applies here. THE OLD SYSTEM. Prior to the adoption of the method hero described colour vision was tested by means of pieces of wool, a none-too-salisfactory method even apart from the difficulties, which some people have in orally defining colours which they see accurately. The wool system had shown that totally colour-blind persons could earn, if not a complete clearance, at least a safe deficiency report. Totally , colour-blind people see the world , largely in black and white, similar to that depicted in moving pictures, but there are degrees of difference by which they experience a “ sensation ” enabling them to define the green of grass, the rod of blood, and so on. ■ Under the old method, when asked to ; pick out a piece of green wool,' by the J shrewd association of the grass “ sensa- i tiou colour,” it was possible for a < colour-blind being to separate the right 1 piece of wool, and so with other pri- 1 inary colours. Dr Shinobu Ishihara has 1 stopped that. I