Color Vision Defects in School Going Children

Introduction : Color vision defect can be observed in various diseases of optic nerve and retina and also a signiﬁ cant number of people suffer from the inherited condition of red and green color defect. Methods : A cross-sectional descriptive study was designed with purposive sampling of students from various schools of Kathmandu Valley. All children were subjected to color vision evaluation using Ishihara Isochromatic color plates along with other examination to rule out any other causes for color deﬁ ciency. Results : A total of 2001 students were examined, 1050 male students and 951 females with mean age of 10.35 (±2.75) and 10.54 (±2.72) respectively. Among the total students examined, 2.1% had some form of color vision defects. Of the male population, 3.9% had color vision defects while none of the female was found with the deﬁ ciency. Conclusions : The prevalence of color vision defect in Nepal is signiﬁ cant and comparable with the prevalence quoted in studies from different countries.


INTRODUCTION
Color vision is one of the important components of visual perception; signifi cant populations suffer from an inherited condition of red/green color defects besides other seen in different retinal and optic nerve diseases. 1 Similarly people with abnormal colour vision are reported to have a signifi cantly higher rate of road accidents. 2 As visual medium is used more in teaching learning activity, child with color vision defect may be at disadvantage when compared with normal children; signifi cantly lower school achievement as assessed by school marks has been reported for children with abnormal colour vision compared colour normal children. 3 Various professions require normal color vision, anyone who is color blind should be advised against training for such occupations as pilots, certain jobs in armed forces, electrical jobs, navigators, police. 4 Histopathologists and medical scientifi c offi cers can be at a considerable disadvantage in work if they have impaired color vision. 5 Color Vision Defects in School Going Children Therefore, a study was conducted at different schools around Kathmandu to evaluate all students studying there for color vision.

METHODS
A cross-sectional descriptive study was designed to evaluate the color vision of children. A purposive sampling of various schools of Kathmandu Valley was done after taking consent from the school authority as well as the students' guardians for the examination. A team comprising of Ophthalmologist, Optometrist and Ophthalmic Assistant visited four different schools around the Kathmandu valley for evaluation.
All the willing students from grade one to ten of these schools were included in the study. Every child was examined thoroughly including visual acuity with the help of internally illuminated Snellen's Vision Chart, anterior segment evaluation with the help of slit lamp (Haag Streit 900). The posterior segment was evaluated with the help of direct ophthalmoscope and/or Slit Lamp biomicroscope with +90Ds lens. Students who had signifi cantly reduced visual acuity (< 6/60) even after refractive correction and any ocular pathology which could affect their performance in color vision screening were excluded from the study and referred to base hospital for further evaluation.
The Isihara pseudoisochromatic plates were used to evaluate the color vision of children under natural day light condition. The number plates of the Ishihara chart were used and the abnormality was differentiated accordingly. The data obtained was entered and tabulated for statistical data analysis. Microsoft Excel was used for the purpose.
Those having any color vision defects were called back to base hospital along with their guardians where further evaluation was carried out to rule out any acquired cause for the defect. Proper counseling was done regarding the different aspects of disorder such as course of the disorder, the adverse affect it can have on the person's choice for future career and inheritance to their offspring as well as possible defect in other family members.

RESULTS
A total of 2001 students were evaluated from four different schools of the Kathmandu valley among which 1050 were males and 951 females (Table 1).
Among all the students evaluated 41(2.05%) were found to have some kind of color vision defects. No obvious acquired cause for color vision defect was observed. All the students affected were males, which is 3.9% of total male population ( Table 2). None of the female students examined were found to have any form of color vision defects. Among the 41 students having color vision defects, six were found with total color blindness, 34 were found to be Deutan and rest Protan (Table 3).

DISCUSSION
The prevalence of congenital color blindness of 3.9% among male population is similar to the prevalence of color blinds in different reports from various countries. A study among school children of Patiala city, India reported 3.85% males and 0.38% females to be colourblind. 6 In study of type of color blindness in Ethiopian population, 4.2% of males and 0.2% of females were found to have various forms of color blindness. 7 Similar study in Jat Sikhs of Patiala city of India, reported an incidence of 3.83% and 0.13% in males and females respectively. 8 A school based study among secondary-school students in Tehran using Ishihara plates reported color vision defects in 8.18% of males and 0.43% in females 9 which is more than twice the prevalence found in our study. Similarly a study in Korean population reported congenital color vision defects in 5.9% of male and 0.44% of female population. 10 Regarding various types of defect, Zein ZA found 3.2% deutans and 0.9% protans among Ethiopian males. In this study also 3.25% of males were deutans while 0.09% protans. 7

Shrestha et al. Color Vision Defects in School Going Children
These different studies indicate the prevalence of congenital color vision defi ciency to be 2-6% in male population with very minimal of female being affected. So the trend is similar in our country as well. The incidence of male being affected is explained by the X-linked genetic inheritance pattern of the disorders; in which males are affected and female are carrier. The inheritance pattern of Y-linked and sometimes with confused pattern in others have also been reported in very few persons, this possibly explains the number of female population affected. 11 No female were found to be affected in this study.

CONCLUSIONS
Signifi cant male population suffers from the congenital color vision disorder. Those with congenital color vision disorder should be properly counseled regarding diffi culties in everyday work, their future profession, genetic inheritance to their children, which would prepare them for the any future challenges and confusions.