INCIDENCE OF FLOUR BLINDENSS AMONG UNIVERSITY STUDENTS

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INCIDENCE OF FLOUR BLINDENSS AMONG UNIVERSITY STUDENTS

ABSTRACT

Colour vision deficiency and colour blindness are synonymous terms describing poor colour discrimination by the visual senses. Congenital colour vision defects are common, x-linked inherited, non-progressive and untreatable disorders. Elsewhere, screening for these disorders are an established practice so that those affected can be advised about occupational preclusions. However, population-based study on the broader impact of colour vision defects is limited. A descriptive crosssectional survey was conducted using Plates 1-17 of the 2008 edition of the Ishihara’s colour album. The study was undertaken in Ugep, a rural community in Cross River State, Nigeria. A convenient sample of 1500 male and female subjects ranging from 10-60 years of age was used and the selection was based on cluster sampling. The study reveals that the prevalence of congenital colour vision deficiency in Nigerians living in Ugep is 1.87%(28 of 1500 subjects) and that of total colour blindness is barely 0.20%. The gender distribution of colour blindness in the sample 2.8% for males and 0.7% for females indicates a significantly greater frequency of defect among males than females (p<0.001,df=1). The distribution of colour blindness based on age brackets 10-20,2130,31-40,41-50,51-60 years was 16,2,1,9,0 and this reveals no sequence between age and the defect (p<0.001,df=1). The findings which serve as base line data for the area under investigation are inconsistent with Nigerian samples reported for other regions in the country but the regional variations are not accounted for. Populationbased screening for colour vision deficiency helpful for prevocational counselling is recommended.

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND TO THE STUDY

Colour identification is one of our most important visual abilities and nearly everyone including colour vision defective individuals can see colour and make discriminations based on colour. This general tendency seems to query the rationale for screening colour vision and minimizes the benefits derived from available reports on colour blindness.

In the course of studying normal colour vision, investigators have observed a wide range of colour discrimination ability especially under such circumstances as the absence of cues, poor illumination, working at speed and viewing objects that subtend a narrow angle at the eye. It is further observed that colour vision defectives show colour vision deficits when compared with those with normal colour vision (Ishihara, 2008; Williams et al, 1998; and Balasundaram and Reddy, 2006). However, some claim that colour vision deficiency does not interfere with daily routine or lifestyle since a reduced visual acuity is not associated with it. Most people with colour vision defects develop effective adaptive strategies and behaviours, and they use other cues such as colour saturation, to deal with any potential limitations in their professional personal life. This makes it possible for most colour blind individuals not to be aware their deficiency (Holroyd and Hall, 1997). Others speculate that clinicians are reluctant in colour vision investigations because should a congenital deficiency be identified there is no treatment for those affected (Adams and Haegerstrom, 1987).

Ishihara(2008) identified colour vision deficiency of congenital origin as the commonest form of colour vision disturbances and explained that most cases of congenital colour vision deficiency are characterized by a red-green deficiency which may be red colour blindness(protan defect) or green colour blindness(deutan defect). The main peculiarity of redgreen deficiency is said to be the fact that red and green colours appear as grey or dark while blue and other colours appear remarkably clear. The application of this peculiarity to the test for colour vision deficiency is the distinguishing feature of Ishihara test which is used to survey the prevalence of congenital colour vision deficiency in Ugep.

The use of Ishihara colour album has been practiced routinely for many years as screening tools for the assessment of congenital colour vision deficiency. Besides their role as simple diagnostic devices, they are of sufficient sensitivity to allow investigators use the results in a clinically meaningful way.

1.2 STATEMENT OF PROBLEM

The screening of colour vision is not well appreciated and even clinicians often conduct only a cursory examination of this aspect of vision. Perhaps, this is because it is generally believed that colour blindness is a minor inconvenience without any functional disadvantage on an individual (Cumberland et al, 2004). More so, in a society where there is less social discrimination coupled with increasing emphasis on equal opportunity, people with impaired colour vision are allowed to undertake jobs that require critical colour judgment. Hence, many do not consider the need to assess their colour vision status.

However, the problem situation is that most of the items in daily use, including colour computer monitors, colour pictures, symbols and printed matter are coloured materials that place a demand on us to interact with and distinguish numerous shades and tints of colour. Again, the rising technology poses basic challenges. Firstly, several careers now require critical colour judgment and employees are thus expected to possess fine colour discrimination ability. Secondly, there is continuously lower cost of colour printing that makes available more coloured materials and further increases our chances of relying on our colour vision function. The situation tends to be critical in that what is largely available is the extrapolations of prevalence of colour blindness not based on specific data sources. Such estimates have very limited relevance to the actual prevalence of colour blindness in any region.

1.3 SIGNIFICANCE OF STUDY

Counselling a subject concerning colour vision defect is an important component of colour vision testing. Therefore, the present survey may help to control the handicap of colour vision deficiency when used for counseling subjects concerning the effects of defective colour vision on daily routine of life, learning progress and effectiveness in occupations that require critical colour judgment. Also, those who are congenitally colour defective may be unaware of their own deficiencies and early diagnosis is valuable not only in this respect, but also in planning vocational choices (Taylor,1971). Again, an assessment of colour discrimination helps to determine the functional and structural intactness of the sense of vision (Tusa and Newman, 1995). Finally, the study might provide a basis for comparison of the prevalence of colour blindness in the area under investigation with what is observed in other areas as researchers attempt to formulate hypotheses on the significance of colour vision deficits in human populations.

1.4 PURPOSE OF STUDY

The aim of the study is to assess the status of visual perception of colour among individuals in the study area.

1.5 OBJECTIVES OF STUDY

To determine the prevalence of colour vision deficiency in the study area.

To verify the claim that total colour blindness is a rare condition. To examine the occurrence of colour vision deficiency in the area on the basis of gender and age.