Magnitude and determinants of refractive error among school children of two districts of Kathmandu, Nepal.

PURPOSE: The purpose of this study is to assess the magnitude and determinants of refractive error among school children of Lalitpur and Bhaktapur districts in Kathmandu Valley of Nepal.
MATERIALS AND METHODS: A descriptive study was carried out in 2003 in four schools; two in each district. A detailed ocular examination was conducted of all children attending these schools and that included visual acuity testing, slit lamp examination, fundus evaluation, retinoscopy, cycloplegic refraction and subjective refraction. Myopia was defined as more than -0.5 D and hypermetropia was defined as error of more than +1 D.
RESULTS: A total of 2000 students of 5-16 years of age were examined. The prevalence of refractive error was 8.60% (95% confidence interval [CI] 7.37-9.83). The prevalence of myopia was 6.85% (95% CI 5.74-7.96). The best-corrected visual acuity was 6/9 or less in the eye of 12.8% children with refractive error.
CONCLUSIONS: Refractive error is of public health magnitude among school children of 14-16 years of age. School screening program in countries like Nepal for early detection of treatable disease is useful to detect and correct refractive error in older students.

Background

Refractive error is an important component of the priority disease “childhood blindness” within the vision 2020’ initiative to eliminate avoidable blindness.[1] The World Health Organization has recommended to its member countries to screen school children at 12-13 years and 15-16 years old so that refractive error could be detected and managed effectively.[2] There are about 5.5 million children in Nepal below 15 years of age. About 3.7 million of them are more than 6 years of age.[3] The Nepal blindness survey that was conducted in 1981 had found that the ocular infection, xerophthalmia and cataract were the leading causes of blindness in children.[4] Although refractive error does not cause blindness, it is one of the preventable causes of visual impairment in children of developing age. Early detection and treatment of uncorrected refractive error enable them to perform better in their daily activities. Limited studies on this issue have been conducted in Nepal in the past. A study in Mechi zone of Nepal was conducted in 1997 and it reported that 2.9% of children had visual morbidity, of which 56% was due to refractive error.[5]

In Nepal, the school screening program is conducted in limited urban areas. The marginalized segment of the population of rural are rarely evaluated. Hence, this study was conducted to assess the magnitude and determinants of refractive error in school going children.

Materials and Methods

A cross-sectional descriptive study was carried out in four schools of rural areas of Bhaktapur and Lalitpur districts of Kathmandu valley. The study period extended from March 2002 to July 2003. The school board was briefed in advance and necessary arrangements were made to carry out the project. The children attending four schools in Kathmandu valley two each from Bhaktapur and Lalitpur districts were our target population. The students were selected from grade I to grade X in these schools. The study team consisted of an ophthalmologist, a resident ophthalmologist, an optometrist and an ophthalmic assistant. All members were explained about the program and its objectives in details. An ophthalmic technician tested visual acuity unaided, with pinhole and with glasses. Ophthalmologist and resident ophthalmologist performed detailed ocular examination. Optometrist carried out refraction and subjective correction.

Brief history from each student was taken. Visual acuity was tested using internally illuminated vision drum (Appasamy, India) and Snellen's illiterate “E” chart held at 6 m distance from the child. Visual acuity was tested without correction, with pinhole, with correction and if applicable, with their spectacles. Extraocular movements and cover test were performed using torchlight. Convergence test was carried out using royal air force rule. Indirect retinoscopy was performed first for all children. Retinoscopy after cycloplegia was done only if hypermetropia was noted or fogging suggested the presence of accommodative spasm. To perform subjective refraction, we used trial set and Universal trial frame (Nikon). A cycloplegic refraction was followed by subjective refraction after 3 days. The drug used for cycloplegic refraction was 1% tropicamide twice at an interval of 10 min. Indications for cycloplegic refraction were: (1) All children up to 7 years of age, eyes with hypermetropia and myopia of six diopter and more, (2) If retinoscopy findings and subjective refraction findings were not consistent with each other and (3) children with best corrected visual acuity (BCVA < 6/9) after dynamic refraction.

Detailed examination of anterior segment of the eyes was performed by using hand held slit lamp (Clement and Clark). For retinal evaluation (if needed under mydriasis), we used direct ophthalmoscope (Heine, Germany). Cases were subsequently referred to B. P. Koirala Lions Center for Ophthalmic Studies for further evaluation.

Diagnosis of myopia was made if it was more than −0.5 D. Hypermetropia was recorded if it was more than +1.0 D after cyclopegic refraction. Astigmatism was recorded if it was more than 0.5 D. Diagnosis of Amblyopia was made if the vision was 6/9 or worse with best correction and after a careful eye examination including fundoscopy through the dilated pupil and cyclopegic refraction.

The data including personal profile visual and ocular status and visual aid given was collected in the pre-tested form. It was formatted using EPI6. Univariate analysis by parametric method was carried out to calculate frequencies, percentage proportions and their 95% confidence intervals (CI). The percentages of male and female were compared and for this we calculated odd's ratio (OR). The significance of age group variation was calculated using Chi-square values.

All students found to suffer from refractive error were offered visual aids at concession rates. Those found to suffer from eye diseases were taken to the eye unit and were treated free of cost. The data of eye examination was used to improve eye care of school students.

Results

A total of 2054 children attending four schools were enrolled. Fifty four (2.62%) students were absent or not willing to participate. A total of 2000 students were examined. The profile of participating and enrolled students is given in Table 1.

Table 1

Representativeness of study participants

The frequency, percentage proportions with 95% CI of refractive error by variants and type are given in Table 2. The prevalence of myopia was 6.85% (95% CI 5.74-7.96). The prevalence of refractive error was 8.60% (95% CI 7.37-9.83). The refractive error in female students was significantly higher than in the male students (OR = 1.58 [95% CI 1.14-2.19]). Students of “14-16 years old” had significantly higher rates of refractive error (χ2= 36.2 degree of freedom = 2 P < 0.0001).

Table 2

Prevalence of refractive error

Myopia and myopic astigmatism among students of different age groups was further assessed. Of 250 “5-7 years” old children, one child (1.0%) had myopia. Among 436 children of “8-10” years of age, 15 (3.4%) had myopia. 43 of 502 “9-11 years” old children had myopia with prevalence of 8.8% while the prevalence of myopia was as high as 10.3 among’14-16 years old children (88/812).

Myopia of more than six diopters was noted in only one student. However, 25 students (18.2%) had myopia between −2 D and −6 D causing significant visual disability and 111 students (81%) had myopia <−2 D. Thirteen (7.55%) students had significant visual morbidity with astigmatism. Ten (5.9%) students with refractive error had hypermetropia of ≥+1.5 D and 12 (6.9%) students had hypermetropia of <+1.50 D.

Forty six (26.7%) students had uncorrected visual acuity between 6/24 and 6/60 while 14 (8.1%) students had visual acuity < 6/60. Twenty-two (12.8%) students had BCVA of < 6/9.

Discussion

The prevalence of refractive error was 8.6% in the study population. In the Nepal Blindness Survey, the researchers had noted visual impairment based on the pinhole correction and its prevalence was 1.3%.[4] However, the magnitude of refractive error was not measured. Another study conducted in Eastern Nepal found refractive error in school going children to be less than 3%.[5] This difference in the prevalence's of refractive error may be due to the fact that previous study were conducted in the communities where as our study is conducted in schools. It may also be due to the fact that Nepal Blindness survey was conducted before 15 years and was a population based study, whereas, the study in Mechi zone involved definite geographical locations and included different ethnic groups even though it's study population was of comparable age group (5-15 years).[45] Ironically, our findings match well with the findings of studies in other countries. The prevalence studies of refractive error had a population of comparable age group (5-15 years) and they were 12.8% in China,[6] 15.8% in Chile[7] and 7.4% in Delhi.[8] On the other hand, a study in rural Tanzania focusing on the primary school children between 7 and 19 years of age found that refractive error (1%) was not a significant public health problem.[910]

Myopia was the most common refractive error followed by astigmatism and hypermetropia in decreasing frequency. The rate of myopia was seven folds higher in children of 14-16 years compared with 6-8 years of age. Similar pattern was reported in the Chinese study.[6] Hypermetropia was 2.33% in children with age 5-7 years and it was 3.49% among children of “14-16 age-group.” One of the most important finding of the study was that 12.8% of children with refractive error had BCVA of < 6/9 in one eye or other and had already developed amblyopia. This finding is comparable with other studies from Eastern Nepal (9%),[5] Chile (6.5%)[7] and in China (5%).[6] The grade of refractive error was directly related to the severity of reduction in visual acuity. This is in contrast to finding in the Chinese study, which showed no comparison between the degree of refractive error and visual acuity.[6]

In our study, female had a higher risk of refractive error than male. Studies in Nepali and other Asian children also had similar observations.[568] The underlying cause of this gender variation should be explored further and refractive services in Nepal should be gender sensitive for making it more effective.

A meta-analysis on vision screening suggested that more evidence-based information should be collected on usefulness of refractive services through school screening system.[1112] In countries where access to eye care services is easy and affordable, cost-effectiveness of vision screening should be evaluated prior to applying policy of vision screening for all school students. School screening in Qatar suggested that students suspected with refractive error should be referred to the nearest eye care unit to make it more efficient.[13] Our study was in underdeveloped areas with limited access to eye care services and hence the yield of the project suggested that such initiatives should be expanded to other districts of Nepal also.

In areas where developmental checks for preschool children are not established, screening the students at the time of school entry is useful in detecting avoidable/manageable ocular pathologies and thus preventing avoidable visual disabilities. As in the study area primary eye care in yet to be incorporated in the primary health system, such initiative of screening 6-7 years old school children even though may not detect many refractive errors, it could be useful in identifying such ocular pathologies.[14]

Conclusions

Reduced vision because of refractive error is an important public health problem in school going children of Nepal. School screening program with periodic evaluation in the primary grades seems to be appropriate in countries like Nepal for early detection of treatable disease, whereas screening of students of higher grades might be useful to identify and manage refractive error.