Year : 1976 | Volume
: 24 | Issue : 2 | Page : 12--15
Incidence of congenital colour defects among the population of Rajasthan
OP Kulshrestha, VK Madan
Department of Ophthalmology, Military Hospital, Jaipur, India
O P Kulshrestha
Department of Ophthalmology, Military Hospital, Jaipur
|How to cite this article:|
Kulshrestha O P, Madan V K. Incidence of congenital colour defects among the population of Rajasthan.Indian J Ophthalmol 1976;24:12-15
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Kulshrestha O P, Madan V K. Incidence of congenital colour defects among the population of Rajasthan. Indian J Ophthalmol [serial online] 1976 [cited 2022 Jul 2 ];24:12-15
Available from: https://www.ijo.in/text.asp?1976/24/2/12/31526
Anomalies of colour vision are usually congenital defects, transmitted as sex linked recessives by two pairs of genes in the nonhomologous part of the chromosomes occurring typically in males and transmitted by females.
From time to time various studies have been carried out to know the incidence of colour deficiencies of congenital type at various places. The incidence is shown to be remarkably constant among western countries, but other races have shown considerable variations.
Various colour blindness studies carried out in different parts of India though not extensive, reveal the frequency of defects between 3 to 5 per cent.
Considering, to the best of our knowledge, the absence of literature reporting the incidence of colour defects in Rajasthan, this study was undertaken on 1138 males belonging to this State, who were selected from ophthalmic outpatient department, Rajasthan Armed Constabulary units, and recruits coming for enrollment to regular and territorial army.
Material and Methods
The tests for colour defects were performed by using Ishihara Pseudo-isochromatic plates numbering I to 25 of the 38 plates, 14th revised edition of 1959. Illiterate people were tested on plates numbering 26 to 38, but this procedure was observed to be very time-consuming on them, the results also seemed to be fallacious probably because of poor understanding of the test by them (illiterates). The data compiled in this study, therefore, include only of literate persons who could at least read the digits.
The test was carried out in various sittings. On each occasion, all the individuals were gathered and what was going to be done was explained. The testing was done during the day time avoiding direct sunlight as per the procedure recommended by Cavanagh in his paper "The Ishihara test and defects of colour vision" written in 1956. The limitations of Ishihara test, the necessity of care in administering it and in evaluating a subject's performance, which has been demonstrated in studies5,13 were kept in mind while carrying out the present study.
The plates Nos. 1, 2, 6, 7, 11, 14, 15, 19, 21 and 23 with their black mounting were kept on a table covered with white table cloth in a little forward inclined position, to achieve a plane of the plate at right angle to the line of vision of testee. The testee was made to sit on a stool in front of table, at such a height so as to get 60 cms. plate eye distance. The sequence of the above serial number of plates was maintained throughout.
Each individual was given 5 seconds to see each plate. The plates not read or read wrongly were again presented for 5 seconds and if still not read or read wrongly, such individuals were then presented all the plates from 1 to 25 by turning the plates in the book and the results recorded.
All those found colour defective were further subjected to Edridge Green Lantern Test to evaluate the efficiency of the later. The Lantern Test was carried out in a dark room. Various coloured discs were shown in sequence with full aperture, and the testee sitting at a distance of 6 metres was asked to speak out the colour of light visible through the aperture.
I. Ishihara's Test
Out of 1 138 males tested, the largest number i.e. 799 were those belonging to Rajasthan State. The smaller number of 399 belonged to other neighbouring States mostly Uttar Pradesh.
In all. 38 cases were found to be colour defectives in males, 29 falling in the category of Deutans (green-blind), 4 into the category of Protans (Red-blind) and 5 in the unclassified group, because though colour defective, this group could not be categorised into Deutans and Protans by the plate Nos. 22 to 25 [Table 1].
Out of the total of 38 colour defectives (screened from 1138 males) 21 individuals were originally from Rajasthan, mostly belonging to Rajput and Jat communities and 17 were from other States.
Out of 21 colour defectives, screened from 799 Rajasthani individuals, 17 were green-blind (Deutans) and four could not be classified. None of the subjects was red-blind.
Out of 17 colour defectives screened from 399 non-Rajasthani individuals, 12 were greenblind, 4 were red-blind (Protans) and I could not be classified [Table 2].
The statistics of colour blindness came out to be 3.33 per cent in the total population tested, 2 62 per cent in the Rajasthan group and 5 per cent in the non-Rajasthan group.
It. Edridge Green Lantern Test
The results of 38 colour defectives detected by Ishihara test and further tested by Edridge Green Lantern Test are as below
(a) The colour marked as Red-A, has been detected as red colour by almost all the cases when viewed through the maximum aperture at a distance of 6 metres.
(b) The colour marked as Red-B, has been confused with yellow or pink by five cases.
(c) The colour marked as Yellow, has been labelled as light red or white by 7 cases.
(d) The colour marked Green, has been labelled as blue by '1 cases and has not been detected by 5 cases.
(e) The colour marked as Signal Green, has been confused with blt.e by 11 cases.
(f) The colour marked as Blue has been detected as blue by all the cases.
(g) The colour marked as Purple, has been labelled as light red by 2 cases and could not be identified by 4 cases.
(h) The effect of mist and rain produced by ground glass and ribbed glass by disc No. 5 was not appreciated by most of the cases. Only 4 cases could answer correctly.
The present study revealed that the frequency of colour blindness in the non-Rajasthani group (5%) and in all cases (3.33%) is almost similar to the average reported by various authors in other parts of this country.
Following few surveys will illustrate the point
(a) Sanghvi and Khanolkar, carried out the study on 700 non-tribal males of Bombay and reported the frequency of colour blindness of 3.7 per cent.
(b) Dronamaraju and Meera Khan, studied in total 569 non-tribal individuals and reported the incidence as 6.5 per cent.
(c) K. Mehra, studied 1023 males belonging to Banaras Hindu University and found 37 persons as colour blind making the percentage incidence as 3.69 in males.
(d) Dutta, in his compilation of extensive study by various investigators of about 10,000 people revealed the incidence of colour defectives as 3.6 per cent.
But the interesting outcome of the present study is the revelation of comparatively low incidence of colour blindness in people from Rajasthan (2.62%) as compared to the people of other States of India reported by various authors.
The cause of very low incidence in the Rajasthanis may be that people belonging to this State especially in the arid and semi-arid areas are subjected to the operation of natural selections as seen in primitive population, which was suggested by Post in his classical theory. To the best of our knowledge we have no report by any other author in this part of the country and on this community, to substantiate our findings.
As we also undertook to study the colour defective persons by Edridge Green Lantern, our aim was not to first screen out the colour defectives from normal with this preliminary quick test and then to confirm them on a comparatively better Ishihara's pseudo-isochromatic plates, but it v as purely to find out how much accurate Edridge Green Lantern test is, if performed alone.
The study revealed that it was difficult to make people understand the colours other than the three primaries. Each person has his own name to give to a particular colour; for example very few could mentally appreciate the difference between green and the signal-green. Similarly, many people would normally consider blue and purple as one colour with difference in intensity and many would express it in their own different language unless specified, to choose from two set words like 'Neela' and 'Bengni'.
Most of the colour defectives were able to appreciate the three primary colours. Almost all colour defectives including red-blinds were able to detect red colour in the disc marked Red-A. Out of 38 colour defectives and mostly green-blinds, 26 could correctly label green as green, only 7 detected them as blue and 5 people could not name this colour.
These results clearly signify that the Edridge Green Lantern Test could not even correctly detect the colour defectives, when people known to be colour-blinds as tested by Ishihara, were subjected to this test. It passed many colour blinds as normals. Therefore, if used alone as colour detecting device, can miss many colour defectives and is in no way a better test than the Ishihara's pseudo-isochromatic plates test. Linksz also remarked about this test that the lantern test can be passed by all except the most severely colour defective persons.
A survey of colour defectives using Ishihara plates (1959 edition) in Rajasthan showed over all incidence as 3.33 per cent and incidence in Rajasthanis as 2.62 per cent. The comparative study of tests with Edridge Green Lantern and Ishihara, revealed the non-reliability of the Edridge Green Lantern Test if performed alone to detect the colour blinds.
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