Colour vision is prominent in understanding the visual world, and it is highly important in many occupations. For example, deuteranomals and protanomals are not able to distinguish the red and green traffic signals because their perception of these lights is poor. Also, red–green colour deficient persons working with electrical cables and telecommunication cannot clearly distinguish the red, brown, orange and green cables. Also, a high number of people with CVD have problems telling the ripeness of fruits. As a result, people living with CVD are barred from certain occupations to prevent potential job hazard and/or for quality assurance purposes [16,17,18,19].
This study highlights the prevalence and genetics of CVD among Nigerian tertiary institution students in Lagos state. The overall prevalence of colour vision deficiency in the present study was 2.85%. This is in agreement with the findings of Mitiku et al. [20] who reported 2.85% CVD prevalence among students at Hawassa University, Ethiopia. Other studies from Nigeria and other countries that somewhat agree with this result include those of Aprioku and Awoyesuku [21] among secondary school students in River state, Southern Nigeria. Balasundaram and Reddy [22] also reported a prevalence of 2.6% among primary school children in Selangor, Malaysia. Similarly, Oduntan et al. [1] reported a prevalence of 2.5% in the research carried out among selected primary and secondary students in Lagos. The slight differences noted may have been as a result of the differences in sample size.
Differing from this study, Chia et al. [23] reported a higher prevalence (5.3%) among Singaporean children while Kim et al. [24] observed 5.9% among Korean males. The incidence of CVD in the present study is also lower to those reported among school children in Central [2] and Southern Ethiopia [25] with prevalence of 4.2% and 4.1%, respectively. Furthermore, Shah et al. [9] reported a higher prevalence (5.8%) in Manipur, India, compared to our result. On the contrary, a study by Ugalahi et al. [26] had a lower prevalence of 2.3% among secondary school students in Ibadan. Abah et al. [27] obtained a lower prevalence 1.5% among schoolchildren in Zaria, Northern Nigeria. Likewise, Ayanniyi et al. [28] reported a lower frequency of 1.2% in Ilorin. No case of total blindness was found in this study which conforms with the view this particular type of vision deficiency is a rare autosomal trait. The difference in the occurrence of colour vision deficiency in the present and previous studies may be attributed to several factors such sampling and analytical techniques as well as racial differences [20, 25]. Studies have shown that the prevalence of red/green colour blindness is different among different races, tribes and ethnicities as higher prevalence had been documented among Caucasians compared to African populations [7].
In the present study, fewer females than males are colour vision deficient in all the studied institutions. The prevalence of CVD ranged from 2.99 to 5.61% among males and between 0 and 2.94% among females indicating a gender-specific pattern of inheritance. The reported prevalence of CVD 4.29% among the male students is in tandem with the results obtained in different Indian populations [11, 29]. Similarly, several authors have reported higher prevalence of CVD among males than females [30,31,32]. The higher incidence of this disorder among males is not unexpected since colour blindness is an X-linked recessive disorder. This type of trait usually affects more males than females because males have one X chromosome; hence, there is no second X chromosome to counter the effect of the recessive allele. Females will have to be homozygous recessive to exhibit the disorder. The single X chromosome in males, if affected, is predominant to colour blindness, while females with two X chromosomes can compensate for an affected X chromosome, thereby decreasing the risk of CVD.
This study further shows that deutan occurs in higher percentage than protan. The overall incidences of deuteranomaly and protanomaly are 18 (1.51%) and 16 (1.34%), respectively. Deutan was the most common type of CVD when compared among the different gender, with a rate of 2.33% among male and 0.79% among females. The prevalence of protan was 1.97% among males and 0.79% among females. This finding is in arrangement with several researches carried out in various countries such as Jordan [33], India [34] and River state, Nigeria [21], where the most prevalent pattern of CVD was the deutan type.
A 1998 study by Bowmaker [35] pointed out that the most common form of anomalous colour vision is deuteranomaly. Deuteranomaly has been reported as the most prevalent type of red–green colour anomaly by several authors [36,37,38]. Individuals suffering from deuteranomaly and protanomaly find it difficult to perceive red, orange, brown and green colours; they only recognize blue and white colours. Individual with this defect can experience hardship in everyday life as colour perception is important to an individual in understanding the visual world. Different factors contribute to the prevalence of CCVD between different populations and regions, and this factor includes population movement, the molecular genetics of the gene on the X chromosome, and natural selection.
In this study, colour blindness in the combined student’s population is more prevalent among the Yoruba ethnic group (3.57%), followed by the Igbo ethnic group with 2.62% and Hausa’s 1.45%. Diverse frequencies of colour vision deficiency have previously been reported for different ethnic groups, race and tribes [15, 20]. In a separate study, the frequencies of 1.81% in Northern Nigeria are predominantly occupied by the Hausas, 3.3% in the Yoruba’s south-west Nigeria and 2.11% in the Niger delta region. Among the colour-blind subjects, the incidences of deuteranomaly and protanomaly vary per ethnic group. Overall, deutan incidences range from 1.45% in the Hausa population to 1.75% in the Igbo subjects, while protans vary from zero per cent in Hausa to 1.86% in Igbo. Other population groups have a joint 0.52% prevalence for protanomaly and deuteranomaly. It can be stated that there is no significant difference in the prevalence of colour blindness among Nigerian populations notwithstanding the geographical differences. Odeigah and Okon [39] posited that the prevalence of colour blindness cannot be accounted for based on ethnic composition of samples.