|Year : 1987 | Volume
| Issue : 2 | Page : 71-73
Colour blindness-A rural prevalence survey
Laxmi Smruti, 773/1-A, Erandawana, Near Kamla Nehru Park, Pune-41 004, India
Laxmi Smruti, 773/1-A, Erandawana, Near Kamla Nehru Park, Pune-41 004
Source of Support: None, Conflict of Interest: None
Colour vision is important for aeroplane pilots, motor drivers, seamen and signal men for their professional work Not much of attention has been paid to population studies of colour blindness as there is no interference with daily routine in majority of persons However there is a need to undertake community wide prevalence surveys which could be useful in study of other genetically transmitted diseases
|How to cite this article:|
Natu M. Colour blindness-A rural prevalence survey. Indian J Ophthalmol 1987;35:71-3
Colour blindness is a commonly used misnomer to denote abnormalities of colour vision. A person is usually colour blind without being aware of it as his vision is otherwise normal The defect is mostly congenital affecting both eyes due to genetic transmisison, but few acquired cases owing to disease of the visual system have been noted. Because of its X-linked recessive inheritance, colour blindness prevalence is used as a marker in genetic transmission studies, in the community and hence the importance of wide cross-sectional, repeat, prevalence surveys.
Available local data were found to be restricted to examination of various categories of students in urban areas . The study was therefore under , taken with a dual purpose to find out the incidence of colour blindness in a rural community of Pune District - Primary Health Centres Wagholi, Paud and Khadakwasla and to train the intern doctors posted at these places in research methodology and community approach.
| Subjects, material and methods|| |
i) The survey was carried out during 1984-85.
ii) Intern doctors posted at Primary Health Centre, Paud Khadakwasla and Wagholi were oriented with conduction of survey in the Department of Preventive and Social Medicine.
iii) Village/vastis/wadis under the 3 Primary Health Centres were covered by house to house visits Relevant information was collected in pretyped proforma The examination of all individuals above 8 years present in the house at the time of visit was done.
iv) Colour Vision was tested by using pseudoisochromatic plates of Ischihara ,. Many villagers were illiterate and figures in the charts were in English Colour vision of such individuals was tested by asking them to trace with a pencil, the pattern of the number, in the plate shown Care was taken to avoid direct sunlight or use of electric light to avoid interference in reading colour shades .
v) Repeat testing of all family members was carried out when a colour blind person was detected.
| Results and Discussion|| |
Colour blindness discovered by a colour blind scientist John Dalton is classified according to Trichromatic theory of Young Helm Holtz. Colour appreciation depends upon differential stimulation of 3 types of cones The abnormality pattern detected depends upon the malfunction of a particular type of cone. Some individuals are thus unable to distinguish certain colours whereas others have onlya colour weakness 1) Monochromatism is a rare condition, (rod monochromat with no cone function) where colour vision is completely lost and the whole spectrum is seen in shades of gray. II) In Dichromatism one of the 3 primary colours is not perceived and colour matching is done with the two remaining colours Thus protanopes are insensitive to red, deutaranopes to green and tritanopes to blue. Ill) All primary colours are seen but sensitivity to one of them is low in Trichromatism.
The current evidence however, instead of supporting the separate pathways theory, suggests presence of a coding process in the retina for conversion of colour information.
| Prevalence|| |
Population coverage in the Primary Health Centre Papud and Khadakwasla was not adequate due to non-availability of a vehicle Vision testing was not done for young children below 8 years of age.
The generally accepted incidence of colour blindness is 8% in males and 0.69% in females ,[6). The low prevalence observed in the present study could perhaps be attributed to racial variation or to difference in detection methods Due to unavailability of an `Anomaloscope' only rough quantification of degree of defect was possible with the help of an Ischihara chart Many cases of subnormal perception due to Trichromatism might have been missed. Out of 596 colour blind male individuals 205 (34.4%) were Protans and 391 (65.6%) were Deutans.
| Age|| |
As the defect was known to be congenital no efforts were made to associate it with age.
| Sex|| |
No case of colour blindness was detected in females The abnormality being inherited as a Xlinked recessive character, males are mostly affected and females usually act as carriers The defect appears in males of every second generation as shown in the figure.
| Race/ Religion/ Caste|| |
The population was racially homogenous The data were scrutinised according to religion and caste to find the influence on transmission of colour blindness in marriages between close relatives No association could be established between prevalence and religion or caste.
| Family aggregation|| |
In 28 families colour blindness was found among brothers.
| References|| |
Kanhere, V .V., Katti, V.A et al, 1975. A study of colour blindness. Science J., Shivaji University, 25: 19.
Belcher, S.J., KW. Greenshields and W.D. Wright 1958. Colour vision survey using the Ishihara, Dvorine, Bostrom and Kugleberg, Bostrom and AO.H.RR tests. Brit J. Ophthal, 42: 355.
Horace, C, Thuline.1964. Colour vision defects in American School children, J.AMA 188: 514-518 May 11.
Joshi, V. G, 1961 Brightness contrast as a source of error in the Ishihara test for colour blindness. Brit J. Physio. Opt 18:239-42; October.
Von, Planta P., 128. Grafes Arch Ophthal. 120: 253-281, Quoted in (3).
Waller, GRM., 1927. Zindukt Abstammhgs Verebungsi, 45: 279-333, Quoted in (3).
[Figure - 1]
[Table - 1]