Vol. 9, No.2 July-Dec 2006 J. Baqai Med. Univ.

Prevalence of colour vision deficiency in a Medical University of Karachi

Qamar Aziz1, Sikandar Ali Shaikh2, Shabana Dammar3

Abstract

Cones in the retina arc responsible for color vision. Colour vision defects (CVD) can be congenital and acquired. Congenital color vision deficiencies are often ignored clinically. It has serious implications in daily life as well as on occupations specially in the medical field. Early detection of this problem can help people in choosing occupations. The present study aims to find the prevalence of CVD in medical students at the start of their career to help them in specialties. A total of 787 medical students were made to read the Ishihara charts in normal daylight. Those who made more than three mistakes in reading from plates no. 10 to 17 were identified as colour vision deficient (red green deficiency). Those subjects who were unable to read any of the plates correctly were labeled as total colour blinds. The subjects suffering from red green deficiency were 1.59%. The medical students suffering from total colour blindness were 0.53%. It is suggested that population screening for colour vision defects (CVD) in schools and medical universities should be carried to help medical practitioners in clinical practice.

Key words: congenital colour vision deficiency, red/green deficiency, Ishihara charts, total colour blinds.

Introduction :

The ability of the eye to see different colours, distinguish humans other species'. Most cases of congenital colour vision deficiency (CCVO) are characterized by red green deficiency.

, Colour vision deficiency is often undiagnosed and may cause problems faced by people with colour vision deficiency affecting their choice of career (33%), job disabilities (25%), recognising road traffic signals (13%) and judgment difficulties in daily routines (75%)2.

Congenital colour vision defects (CCVD) are non-progressive and untreatable disorders. Screening children for these disorders is established practice in the United Kingdom, which help them in choosing a proper occupation 1.

The X-linked Red green deficiency affects approximately 8% of the male population in most Western countries3. The prevalence of CCVO is similar in the medical profession4

.

Few studies have shown the effects of CVO in identifying important clinical signs in clinical practice and the difficulties faced by the clinicians5. Common clinical tests include

• Ishihara plates 2 - 17 from the 38 plate series

• 015 colour sorting test (3 or more cross over errors is I- Asstt Prof of Physiology, 2- Chairman, Dept of Physiology, BMU

a fail)

• Anomaloscopy or 100 Hue test

Ishihara series of plates is designed to provide a quick and accurate assessment of CCVO. Some individuals may fail colour vision screening tests. Therefore, the degree of colour vision deficiency should be evaluated by using quantitative tests . A widely used sorting test is of the Farnsworth Panel 0-15 type3.

The present study aims to find the prevalence of CVO in a Medical University at Karachi.

Subject and Method

A total of 787 MBBS and BOS students of Baqai Medical University were selected. The study was carried out on the four batches of students from the year 2003 to 2006. Among the MBBS students, 292 (52.14%) were females and 267 (47.67%) were males and among the BOS students 83 (36.56%) were males and 144 (63.43%) females. The average age was 19-20 years. The Ishihara charts were used to detect CVO. The subjects were examined in broad daylight during the practical session from 11 am to 1 pm. They were naive to the study. There are a total of 38 plates in the Ischihara chart

' 3- Dept of Physiology, BMU, Karachi. •

Vol. 9, No.2 July-Dec 2006 Qamar Aziz et al J. Baqai Med . Univ.

and plates No. 1 to 25 were shown to the subjects. The plates were held 75 cm. from the subject and tilted so that the plane of the paper was at right angle to the line of vision. The subject read the Ischihara Chart and this was noted down by the examiner. This was compared with the check list provided

. by a booklet on /schihara chart. More than three mistakes from plate no. 10 to 17 were declared as red green deficiency. Those who were unable to read any of the plates were recorded as total colour blinds.

· Results

Out of the totaf#bf 560 MBBS students 11 suffered from CVD (1.%%). Only one of them was a female. Three of

· them (0.53%) were total colour blind and eight had red green deficiency (1.42%) . All the three total colour blinds were males. Among the 227 BOS students 4 were suffering from red green deficiency (1.76%).

The maximum frequency error was of plate No.4 (66.67%). The frequency error of plate no 17 was 53.34%. The frequency error of plate no.3 was 40%. The frequency error of plate no. 5,7,9,14 and 15 were 33.34%.

Discussion

Colour vision deficiency is a serious handicap for many occupations, including medicine and creative arts6.7. Colour vision deficiency is a risk factor for driving8. The studies

have reported a higher prevalence (7.33%). In another study a higher incidence of 6. 7% in males has also been reported 1.

At a population level, corigenital CVD confers no functional disadvantage in relation t6 educational attainment and unintentional injury 15. This challenges the rationale for the value of population screening for these disorders 15• Numerical confusion errors were minimal in the present study in contrast to what has been reported in school children 16 because this study was conducted in adults of a medical university.

It is important that school children should be aware of CYD to help them in planning their career but a significant association between CVD and either educational attainment or the occurrence of injuries especially during work has not been found 15 . Therefore it has been concluded by some researches that normal colour vision is not a prerequisite for safe driving or working, and their findings challenge the rationale of population screening for colour vision deficiency 15.

We conclude that education screening should actually be increased at the start of medical education with improvements so that advice can be provided based on individual needs.

Reference:

I. Cumberland P, J S Rahi C S Peckham. Impact of congenital colour vision defects on occupation. Archives of Disease in Childhood 2005; 90:906-908 .

which have failed to show that it is a risk factor had samples 2. Holroyd E, Hall DMB. A re-appraisal of screening for colour vision impairments. Child Care Health Dev I 997; 23 :391-8.

too small to identify the expected level of risk .

Medical practioners with CCVD arc usually unaware of their problem9. Screening policies in university medical schools 3. for CCYD usually do not exist 10- 12• It has been suggested that practitioners and medical students should be aware of their colour vision deficiency and undergo further test to know the severity of their deficiency 12 .

Practitioners with CCVD identified fewer bacilli than controls 4 . in a photograph of Ziehl-Neelscn stained sputum3. Other have documented the difficulties of laboratory staff with CCVD in the assessment ofhistopathological slides. Therefore 5. practitioners with severe CCVD should take special care to ensure safe clinical practice9

·13

. This will further make them more successful in their careers. These findings will strengthen the growing challenge to establish population screening at the school and university level. 6.

The result of this study is not in accordance with a study of congenital colorblindness on young Turkish m:en 14 as they

John L Campbell, Lewis Griffin, J Anthony B Spalding, Fraz A Mir. The effect of abnormal colour vision onrhc ability to identify and outline coloured clinical signs and to count stained bacilli in sputum . Clin Exp Optom2005; 88: 376-381.

Stalding JA. Colour vision deficiency in the medical profession . Br J Gen Pract 1999; 49:469-475 .

Spalding JA. Doc!.ors with inherited colour vision deficiency: their difficulties in clinical work. ln:Cavonius CR, ed. Colour, Vision Deficiency XIII. Dordrccht: Kluwer Academic Publishers ; 1997; 483-489.

Essen J, Fogelman K, Ghodsian M. Long-tenn changes in the school attainment of a national sample of children. Educ Res I 978; 20: 300-5.

Vol. 9, No.2 July-Dec 2006 Qamar Aziz et al J. Baqai Med. Univ.

7. Jefferis BJMH, Power C, Hertzman C. Birth weight, childhood socio-economic environment, and cognitive development in the 1958 British birth cohort study. BMJ 2002; 325: 305-8.

8. Lampe LML, Doster MF, Beal BB. Summary of three year study of academic and school achievement between color-deficient and normal primary age pupils: phase 2. J Sch Health 1973; 43: 309-11.

9. Poole CJM, Hill DJ, Christie JL, Birch J. Deficient colour vision and interpretaion ofhistopathology slides: a cross-sectional study. BMJ 1997; 315 : 1279-128.

. 10. Campbell JL, Spalding JA, Mir FA, Birch J. Doctors and the assessment of clinical photographs- Does colour blindness matter Br J Gen Pract 1999;· 49:459.

· 11. Campbell JL, Spalding JA, Mir, FA. The description of physical signs of illness in photographs by physicians wwith abnormal colour vision. Clin Exp Optom 2004; 87:334-338. .

12. Campbell JL, Spalding JA, Mir, FA, Birch J. Doctors and the assessment of blood glucose testing sticks: does colour blind9ess matter? Br J Gen Pract 2000; 50: 393-395. .

13. · Mortality statistics. Cause 1993. London: HMSO; 1995.

14. Citirik M, Acaroglu G, Batman C, Zilelioglu 0 . Congenital colour blindness in young Turkish men: Ophthalmic Epidemiol. 2005 Apr; 12(2): 133-7.

15. Cumberland P, Rahi JS, Peckham CS . Impact of congenital colour vision deficiency on ducation and unintentional injuries: findings from the 1958 British birth cohort. BMJ 2004; 329: 107 4-5. (6 November).

16. Cosstick M, Robaei D, Rose K, Rochtchina E, Mitchell P. Numerical confusion errors in ishihara testing:findings from a population-based study. Am J Ophthalmol. 2005 Jul; 140(1): 154-6.

Fig 2 : Check list for colour vision defect

Sr. No. No. seen by the Person with red Person wijh total Normal person green deficiency blindness

01 . 12 12 12

02. 8 3 X

03. 6 5 X

04. 29 70 X

05. 57 35 X

06. 5 2 X

07. 3 5 X

08 . 15 17 X

09. 74 21 X

10. 2 X X

11 . 6 X X

12. 97 X X

13. 45 X X

14. 5 X X

15. 7 X X

16. 16 X X

17. 73 X X

18. , X 5 X

19. X 2 X .

20. X 45 X

21 . X 73 X

Sr. No. No. seen by the PROTAN DEUTRAN

normal person Strong Mild Strong Mild

22 . 26 6 (2)6 2 (2)6

23 . 42 2 (4)2 4 (4)2

24. 35 5 (3)5 3 (3)5

25. 96 6 (9)6 9 (9)6

II