Year : 1963 | Volume
: 11 | Issue : 4 | Page : 96--99
Methods of testing colour perception and observations on the same amongst service personnel
Indian Naval Hospital, Bombay, India
Indian Naval Hospital, Bombay
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Venkateshwarlu D. Methods of testing colour perception and observations on the same amongst service personnel.Indian J Ophthalmol 1963;11:96-99
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Venkateshwarlu D. Methods of testing colour perception and observations on the same amongst service personnel. Indian J Ophthalmol [serial online] 1963 [cited 2020 Feb 20 ];11:96-99
Available from: http://www.ijo.in/text.asp?1963/11/4/96/38966
Good colour vision is necessary for navigation at sea and other forms of seamanship. In addition to other requisite physical standards, perfect colour vision is also required for pilots, navigators of the fleet air arm and also for signaling and communication branches of the Navy and Air Force. For the rest of the personnel in the Navy, a reasonably good standard of colour vision is required. Totally colour blind people are not accepted in the Navy, for dangerous situations may arise at times, while at sea, when work has to be guided by colourlights in all branches. In civil life good colour vision is required of engine and bus drivers, signalers among railway personnel and men employed in jobs like painting, dyeing. textiles and telephone lining.
In 1947, Granit had worked out a reasonably satisfactory explanation for colour vision. The Cones, we know are responsible for colour vision. In his experiments of stimulation of visual end organs by microelectrodes, he found out that there are seven to eight varieties of photoreceptors known as discriminators or modulators which can respond to a particular wave length of light. These photoreceptors can again be grouped into three different sets of signalers or dominators. Each set of dominators will respond to a certain degree to each of the primary colours namely red, green and blue. Thus colour produced will be equal to XR + YG - ZV where X + Y + Z = 100 and R = red. G - green and V = violet. The colour perception will depend upon which dominator is stimulated to the maximum. The discharge of impulse is a complicated procedure starting from the dominator photoreceptors through the interconnected bipolar and ganglion cells and through different sets of optic nerve fibers through the external geniculate ganglion, to the occipital cortex, where it is interpreted as colour.
Colour varies in intensity, hue (wave length) and saturation, (admixture with white). Under photopic conditions, the brightest part of the spectrum is at 560 mμ Under scotopic or twilight conditions, there is a shift of this brighter part to 510 mµ The phenomena is known as Purkinje Phenomena.
I. The TRICHROMATS make use of the three primary colours red, green and blue, to match a spectrum. There are subgroups of this state.
a) Protonomalous persons use more of the red end of the spectrum.
b) Deuteronomalous persons use more of the green end of the spectrum.
Together they comprise 4 per cent of all men and 0.3 per cent of all women.
II. The DICHROMATS make use of only two of the three primary colours, to match the spectrum.
a) Protonopes make use of the green and blue but not red.
b) Deuteronopes make use of the blue and red but not green.
c) Tritanopes make use of the long wave end and the middle of the spectrum. They are blue yellow blind.
III. The MONOCHROMATS are again rare, they are achromatic and totally colour blind using only shades of white and grey to match the spectrum. This may be congenital or acquired during a disease process.
Luminosity of the spectrum is practically normal for deuteronamalous deuteronopic persons. The spectrum is considerably shortened for protonomalous protonopic persons. Red end of the spectrum is not seen by them and the brightest part is at 540 mμ.
The term dyschromatopsia is a better term than colour blindness, of which different shades exist, but rarely there is a totally colour blind. This is often hereditary, found mostly in men and transmitted through the females. Rarely these are acquired in diseases of retina, optic nerve as in retrobulbar neuritis and cerebral injuries. Dr. Pandit some time back described a hemianopic colour field-defect in a bus driver following injury to the skull. Central colour field defects are fairly common in retrobulbar neuritis, tobacco and alcohol amblyopia, macular scars and in systemic diseases like diabetes.
The typing of these different varieties of colour perceptions is usually done on an anamaloscope. The Indian Air Force is now working on the same and the results are awaited. In the Indian Navy, a Martin's Board of Trade colour lamp is used. This consists of a 40 watts opal coiled coil, shadow less bulb working on 190 volts D.C. There are three pairs of apertures, 5 mm., 2 mm. and 1 mm in diameter. There is a battery of colour filters consisting of signal red, signal green and pure white, which can be interposed between the aperture and the bulb. The apparatus is mainly used to screen off the dyschromatopes beyond a certain degree particularly amongst recruits and sometimes among serving personnel. No attempt is made to classify them as trichromates, dichromates and monochromates. After doing a preliminary external examination of the eye and testing the visual acuity for distance and correcting the same if necessary with glasses, the candidate is made to sit down at a distance of 6 in from the lamp in a dark room. He is shown the white colour in the two large apertures and is told it is white. He is also told that no colour other than red, green and white will be shown to him and is asked to name the colours from left to right without hesitation. The colour filters are shuffled like a pack of cards each time. The test is carried out for half a minute with a large aperture and another half a minute with the small aperture. If he passes without making a mistake in anyone of these, he is supposed to have colour perception grade one. Fundus examination is then made to look for any disease of macula or optic nerve.
If he fails in the test using the small apertures, the candidate is dark adapted for 15 minutes and is tested again using a single large aperture at a distance of 5 feet for half a minute. If he names the colours without a mistake, his colour perception is standard three. If he fumbles in this also, his colour perception goes to standard four. No man with the last grade of colour perception is recruited or permitted to serve in the Navy. While using the lamp, no mirror is used, as this causes distortion. And no flickering or oil lamp or A.C. current is used for the same reason. Giles-Archers Lamp is a simpler portable form of the above mentioned lamp.
The use of Ishiharas or A.O.C. Pseudo - Isochromatic colour plates are being given up gradually, as their standardized use is more difficult to practice and the results are inconsistent.
There are other devices for testing colour vision, like Hardey Rand Rietlers colour plates and Fansworth Dachotomotous buttons. The latter test is used, if five or more mistakes are made in the former test. The latter test consists of arranging a panel of colour buttons according to their shades and a graph is drawn from it. In the former test the light is made to fall on the colour plates from a 60 watts Macbath Basle lamp "A.B.E. 10" at an angle of 45 degrees and the candidate is asked to read out 18 colour plates similar to Pseudo-Isochromatic.
If a serving personnel fails in standard one of Martin Board of Trade colour lamp and if his trade requires so, he is re-examined three months after treating him with Priscol, Nicotinic Acidamide and Vitamin 'B' complex, advising him to avoid all alcohol and smoking.
Our observations are for a period of seven years from 1955 to 61. Since our candidates are from a controlled population who were screened out once or twice previously, the percentages of colour defects are not the same as in general population. None of the women candidates were found to be having any colour defect. During these seven years, in four candidates the colour perception went down from standard one to three. They were all forty years of age and except one all have improved back to standard one with treatment. We have also found considerable number of persons with macular scars and ninety per cent of them possess colour perception standard one, probably because the crucial cones in the centre were spared.
Two candidates were found to be normal on Ishiharas, but failed in standards one and three on the colour lamp. None of the colour defectives were found to be having any systemic disease or infection. Our results from 1955 to 61 are tabulated in the table below.
The present theory of colour vision has been discussed. The types of colour perceptions and colour defects have been mentioned. The apparatus and the methods of testing colour perceptions as used in the Indian Navy have been described, and a few of our observations are given.
|1||Adler. F, E. Physiology of the Eye 3rd Edition (1959).|
|2||Arthur, Linkz.. Physiology of the Eve (Vision) Vol. I & 11 (1952).|
|3||Samson and Wright, Applied Physiology. 10th Edition (1961).|
|4||Personal Communication from Sqn. Leader Jones.|