Introduction

Emmetropia is the state in which parallel rays of light come to focus on the retina with the eye at rest .Such ideal optical state is common in contrast to the opposite condition ametropia that is often exists. Three main types are considered as refraction errors:hyperopia (farsightedness), myopia (nearsightedness)and astigmatism.₁The prevalence of myopia is currently attracting worldwide attention as many recent studies report dramatic increases over the last 20 years₂,₃.InJordan,approximatly 1/3 of the populaton are in the school age₄. Poor vision in childhood affects performance in school or at work and has a negative influence on the future life of the child. Moreover, planning of a youth's career is very much dependent on the visual acuity, especially in jobs for navy, military, railways and aviation₅. This warrants early detection and treatment of refractive errors to prevent permanent disability.

The present study was carried out in the schools of Tafila city. Students of the age group 12-17 years were chosen because refractive errors were found among 45% of examined schoolchildren in United Arab Emirates ₆And in Al-Baha region of Saudi Arabia.₇ which are some neighboring countries.This study presents the prevalence of refractive errors by age, sex, class, type of error and socio-economic status among school children of Tafila city. The mean age of onset of refractive errors was computed. This information may be used for planning appropriate eye care programme for the high risk groups in order to reduce the burden of visual impairment in the population.

Tafila is a southern city of Jordan. There are approximately 60 schools in the city. Students in the age group 12-17 years studying in classes 7th-12th were included in the study. Assuming a 20% prevalence of refractive errors based on a pilot study, the sample size was calculated to be 1526 for this cross-sectional study. However, 1714 students were selected, of these 67 students remained absent during study period and could not be examined. Students of 10th, 11th, and 12th classes were busy preparing for their examinations so their number was less.

Method

The students were examined in their respective classes. The screening was done in the following way. From 6 metre distance the student was shown the E-card with four E's of standard size (6/9 of Snellen's chart). For each eye the child had to indicate the direction of open end of E.Simply rotating the card, the sequence could be changed. The child either indicated the direction correctly (eye sight good) or incorrectly (eye sight not good). In case of doubt the eye sight was recorded as not good. Children with visual acuity less than 6/9 were sent for subjective refraction test. Subjective refraction was performed by achieving best corrected visual acuity, while Cycloplegic refraction was advised for students when best corrected visual acuity could not be achieved. Students presenting organic defects in eye such as corneal opacity, opacity of the lens, choroid and retinal disorders were excluded from study. It must be mentioned that students were screened only for distant vision. Therefore, the number of hypermetropic students was far less than the myopic ones.

Results

Age, sex and class distribution

Amongst 1,647 students who were examined, 828 were males and 819 were females. The age of the students ranged from 11 to 17 years. The mean age was 13.22 years, median age was 13 years.In this study (417) students (25.32%) were found to have refractive errors. Of these 196 (47%) were females and 221 (53%) were males. There were no significant differences in refractive errors found between males and females

Figure 1

Table 1a: Sex-wise distribution of students with and without refractive errors.

The optical states: myopia was found in 265 (63.5%), hypermetropia in 47(11.2%) and astigmatism in 85 (20.4%) cases (Table 1B).

Figure 2

Table 1b: Optical states

The percentage of ammetropic students in the10th to 12th grades was significantly higher (d value = 3.96, p<0.05) than the percentage of ammetropic students in the 7th to 9th grades(Table II) and the percentage is also increased by increasing age Table III.

Figure 3

Table 2: Class-wise distribution of students with and without refractive errors.

Figure 4

Table 3: Age-wise distribution of students with and without refractive errors.

It was found that most of these children (277) representing 66.4%) were aware of their refractive errors, whereas, 140(33.6%) were unaware of the problem. The mean age of onset of therefractive errors in these cases was 11.22±2.07 years and the median age was 12 years (Table IV)

Figure 5

Table 4: Age of onset of refractive errors.

Discussion

The results of our study are similar to these carried out by Laatkainen₈. It is during this period, the children are at risk of developing refractive errors, because they are actively growing and subjected to the strain of near work due to demanding academic schedules. Such a population is likely have more number of myopics.

In the age groups that we have studied, the prevalence of refractive errors also varies with age. Significant differences in the prevalence between age groups and classes have been demonstrated in our study (tables II and III). In this period, with increasing age, children are subjects to cope with school and academic activities. The increase in prevalence of myopia found in our study is probably related to the increased demands for academic schedules. This could represent a risk factor for developing refractive errors in this age group.

Refractive errors found in our study did not differ significantly between males and females (tab IA). In one study, it was shown also that no significant differences in refractive errors between males and females ₉. However, in other studies₁₀,₁₁ refractive errors were found to be more common in girls than in boys. In these studies the differences were related to the possible differences in the rate of growth between girls and boys. Girls attain puberty earlier on an average and reach their final body weight 1-2 years earlier than boys.

Conclusion

The data support the assumption that vision screening of school children in developing countries could be useful in detecting correctable causes of decreased vision especially refractive errors and in minimising long term visual disability.

Recommendations

The present study shows that the adolescent age represents high risk group for refractive errors. Most of the children are unaware of their refractive errors. Therefore, screening in school and pre-school ages should be carried out periodically. In addition, children in these ages and their parents should be educated about signs and symptoms of refractive errors, ocular hygiene and for the risk factors involved in the development of these errors and other ocular pathological problems. During screening for refractive errors, adequate arrangement and illumination and clarity of the chart must be considered and ocular fatigue should be avoided.