Prevalence of visual impairment in school-going children among the rural and urban setups in the Udupi district of Karnataka, India: A cross-sectional study.

AIM: The aim of this study is to estimate the prevalence of visual impairment among school-going children in Udupi district, Karnataka.
MATERIALS AND METHODS: A cross-sectional study across eleven schools from both urban and rural parts of Udupi taluk was conducted to report the magnitude of visual impairment among the schoolchildren. Complex survey design was used in allocating the sample size through stratification and clustering. Totally 1784 schoolchildren between the age groups of 5 and 15 years participated in the study. Presenting visual acuity and objective refraction was measured using computerized logMAR acuity charts and Plusoptix A09 photorefractor, respectively. Manifest ocular deviation or squint was also recorded.
RESULTS: The mean age of the students was found to be 10.62 ± 2.72 years. The prevalence of visual impairment, i.e., visual acuity worse than or equal to 20/40 in the better eye was found to be 4.32% (95% confidence interval: 3.38%, 5.26%). The prevalence rate was significantly higher among students from urban area (5.6%) compared to those from rural area (3.6%) (P = 0.011).
CONCLUSION: Visual impairment was found to be 4.32% in the school-going population of Udupi district. Effective and user-friendly devices aided the visual deficit screening including refractive error and squint. Copyright:

Introduction

Uncorrected refractive errors are the leading cause of avoidable visual impairment in children. It has emerged as a major public health problem needing effective programs from health-care workforce, education professionals, and caretakers.[1] Multiple surveys conducted among school-aged children across the globe have reported varying magnitudes of uncorrected refractive error burden (Nepal: 8.1%, Pakistan: 8.9%, Malaysia: 17.1%, Iran: 3.8%, South Africa: 1.4%, Brazil: 4.82%, Australia: 10.4%, and Chile: 15.8%). Studies from India show that the prevalence of uncorrected refractive error varies from 2.63% to 7.4%.[2]

Globally, around 12.8 million children in the age group of 5–15 years are visually impaired due to uncorrected or inadequately corrected refractive errors. A prevalence of 0.96% with the highest prevalence in urban and highly developed urban areas in Southeast Asia and in China has been reported.[3] To cater the rising prevalence issue, various school eye screening programs have been evolved in the Indian context[4] majorly under the initiative of the District Blindness Control Society since 1996.[5] To detect subnormal vision at an early stage and to yield the highest benefit from timely referral, emphasis was given to the effective use of instrument-based screening procedures.[67]

This study, therefore, attempted to report the prevalence of visual impairment in the schoolchildren of the southern coastal region of Karnataka with a specific emphasis on refractive errors.

This study also tried to establish the comparison of visual impairment status in rural versus urban population in this geographic location.

Materials and Methods

A school-based cross-sectional study was conducted across urban and rural parts of Udupi taluk, Karnataka. Considering a 5% prevalence of visual impairment from the earlier studies conducted in South India[8] with 95% confidence interval (CI) and 25% of relative precision, the sample size was calculated to be 1168.

Complex survey design

Stratified cluster random sampling technique was used and a design effect of 1.5 was incorporated, and thus, the final sample size came to 1752. A total of 1782 school students were examined. A complete list of schools was obtained from the concerned government authorities, and schools were stratified based on their geographical location to urban and rural areas. Using proportional allocation technique, the required number of students from each stratum was calculated. Schools were selected using simple random sampling technique without replacement using lottery method from each stratum. A total of 1191 students from 8 rural schools and 593 students from 3urban schools were enrolled in the study. An equal proportion of schools (rural and urban) were approached for the study considering the geographic location spread and strength of students. Among them, 8 schools located and listed under the rural setup and 3 schools in urban setup gave their consent to be a part of the study. The educational department classifies schools as urban and rural based on the area of school location, student strength, availability of modern facilities, and the monthly income of parents. Students from Class 1–10 in the age group of 5–15 years and those present on the day of examination were included in the study.

Data collection tool included the measurement of visual acuity with the use of computerized logMAR charts (NHS trust, UK) and Plusoptix photorefractor (Plusoptix A09, Germany) to measure the objective refraction. The field testing for these instruments have been done earlier and reported elsewhere.[91011121314151617] Students with their presenting visual acuity ≤20/40 in the better eye were considered visually impaired,[18] and a cutoff of ≤20/40 in either eye was used to define abnormal vision.[19] Myopia was considered when the measured objective refraction was more than or equal to −0.75 spherical equivalent diopters in one or both eyes. Participants were categorized as hyperopic when the measured objective refraction was >+2.00 spherical equivalent diopters in one or both eyes, provided that no eye was myopic. Astigmatism was considered to be visually significant if ≥1.00 D.[7] However, as the Plusoptix photorefractor gives an overcorrection of 1.50 D for Indian eyes,[17] the calibration factor was incorporated during analysis and reporting the prevalence. The study period was from August 2012 to May 2013 for which the ethical clearance was obtained from the Institutional Review Board. Permission was received from the Deputy Director of Public Instructions for carrying out the study in various schools. The study was conducted in accordance with the Declaration of Helsinki (1964). Individual permission from the school authorities was also taken before conducting the study.

Data analysis

The data entry and analysis was done using statistical software package, SPSS Statistics for Windows, version 15.0 (SpSS lnc., Chicago, ltt., USA). Prevalence was reported in terms of percentage with 95% CI. Univariate analysis for finding the statistical significance of associations was done with Chi-square test. P < 0.05 was considered as statistically significant.

Results

A total of 1782 students were enrolled in the study. The mean age of the participants was 10.62 ± 2.72 years within the range of 5–15 years. The distribution of females was found higher (53.58%) as compared to males (46.42%). Family history of refractive error among the siblings was seen among 44.8% of the students from urban schools and 55.2% from rural schools. Among various ocular symptoms reported, watering was found among 6.7% of the students, followed by blurring for vision or difficulty in seeing blackboard letters 5.4% and 2.8% from eyestrain while doing near activities. Occasional pain and frequent redness of the eyes were also observed in about 2.1% and 1.4% of the students, respectively.

The prevalence of visual impairment was found to be 4.32% (95% CI: 3.38%, 5.26%). The prevalence in the urban area was found to be 5.9% while the same in the rural area was 3.6%. This was tested by Chi-square test with 95% class interval reporting. However, no child was found with severe visual impairment and blindness that was denoted by the visual acuity of ≤20/200 in the better eye [Table 1]. The prevalence of abnormal vision that is visual acuity equal to worse than 20/40 in at least one eye was found to be 8.9% (95% CI: 7.48, 10.12).

Table 1

Distribution of presenting visual acuity in the better eye

Presenting VA	n (prevalence in percentage)	95% CI for prevalence	Urban	Rural
≥20/32 both eyes	1624 (91.1)	89.78-92.42	526 (88.7)	1098 (92.3)
≥20/32 one eye only	81 (4.6)	3.63-5.57	32 (5.4)	49 (4.1)
≤20/40-≥20/63 better eye	62 (3.5)	2.65-4.35	28 (4.7)	34 (2.9)
≤20/80-≥20/160 better eye	15 (0.8)	0.39-1.21	7 (1.2)	8 (0.7)
≤20/200 better eye	0		0	0
Total	1782 (100)		593 (100)	1189 (100)

VA: Visual acuity, CI: Confidence interval

At the time of examination, 47 (2.6%) of 1782 children were wearing spectacles and around 51.1% of the students who were wearing glasses have good visual acuity of 20/30 or better in both the eyes. A total of 29.8% of students wearing glasses have poor visual acuity of 20/40 or worse in the better eye. Furthermore, of the 77 with visual impairment in both eyes, only 14 (18.2%) were wearing spectacles at the time of examination [Table 2].

Table 2

Distribution of students wearing glasses across the presenting visual acuity

Presenting VA	n (prevalence in percentage)	Wearing glasses, frequency (%)
≥20/32 both eyes	1624 (91.1)	24 (51.1)
≥20/32 one eye only	81 (4.6)	9 (19.1)
≤20/40-≥20/63 better eye	62 (3.5)	12 (25.5)
≤20/80-≥20/160 better eye	15 (0.8)	2 (4.3)
≤20/200 better eye	0	0 (0.0)
Total	1782 (100)	47 (100)

VA: Visual acuity

The distribution of abnormal vision was seen to be almost equal in the age groups of 5–8 years and 9–12 years that is 9.9% and 9.2%, respectively. There was a slight decrease in the presence of visual impairment (7.5%) in the age group of 13–15 years. However, this variation was not found statistically significant (P = 0.421). Furthermore, there was no difference in reduced vision found across males (8.8%) and females (8.9%). A higher percentage of students (11.3%) from urban schools had abnormal vision as compared to students from rural schools (7.7%). This difference was found to be statistically significant (P = 0.011) [Table 3]. Statistically significant association was also seen with the presence of reduced vision and less participation in sports and extracurricular activities (P = 0.001).

Table 3

Distribution of reduced vision across place of residence

Residence	Frequency (%)			P
	VA ≤20/40 in either eye	VA ≥20/32 in both eyes	Total (n=1782)
Urban	67 (11.3)	526 (88.7)	593 (100.0)	0.011*
Rural	91 (7.7)	1098 (92.3)	1189 (100.0)

*p < 0.05 considered statistically significant. VA: Visual acuity

The prevalence of refractive error measured with photorefraction was found to be 12.2% with 95% CI (10.68, 13.72). The prevalence was found higher (15.3%) among urban students as compared to that of students from rural schools (10.7%). Of 216 with the presence of refractive error, 31.9% of children were visually impaired at the time of examination. The prevalence of myopia and hyperopia was 4.0% and 0.8%, respectively, whereas the prevalence of mixed and simple astigmatism was found to be 9.9% with 95% CI (8.51, 11.29).

The prevalence of myopia increased from 1.9% to 5.6% as the age increased from 5 to 15 years, whereas the prevalence of hyperopia decreased from 1.2% to 0.4% as the age increased. The distribution for the presence of either hyperopia or myopia was found to be significantly different across the three different age groups (P = 0.035) [Table 4]. The prevalence of squint was found to be 2.1% with 95% CI (1.43, 2.77). Of 34 students with ocular deviation, 16.7% had visual impairment at the time of examination.

Table 4

Distribution of myopia and hyperopia across different age group

Age group (years)	Frequency (%)				P (Fisher’s exact)
	Myopia	Hyperopia	Normal	Total
5-8	8 (1.9)	5 (1.2)	400 (96.9)	413 (100.0)	0.035*
9-12	35 (4.1)	7 (0.8)	813 (95.1)	855 (100.0)
13-15	28 (5.6)	2 (0.4)	474 (94.0)	504 (100.0)

*p < 0.05 considered statistically significant

Discussion

This study observed the prevalence of visual impairment as 4.32% with a higher prevalence in the urban schools (5.9%) compared to the rural schools (3.6%). This prevalence rate was comparable to other studies reported from India, where the prevalence ranged between 2.63% and 7.4%.[6] Murthy et al.[20] reported the prevalence of 4.9% from urban population in New Delhi, whereas Dandona et al. reported the prevalence to be 2.6% from the rural part of South India.[21] The study done by Kalikivayi et al. among the schoolchildren in South India reported the prevalence as 5.1% which is comparable to our study.[8] The prevalence of blindness and severe visual impairment reported in other studies was at a lesser rate ranging from 0.20% to 0.93%.[82021] A study from the Darjeeling district of West Bengal conducted by Bhattacharya et al. noted a prevalence of abnormal visual acuity of <20/30 in either eye in the 7–8 years of age group similar to the findings in our study where the prevalence is seen highest in the age group of 5–8 years (9.9%).[22] The findings from other studies where a comparison of visual impairment prevalence was done between the rural and urban children showed a similar trend seen in our studies; the rate was higher in urban area compared to that in the rural side.[23]

The methodology adopted in this study was robust as computerized logMAR (COMPlog) acuity was used for the mass screening where the printed distant acuity charts are generally used. The COMPlog computerized clinical visual acuity measuring system of thresholding has been tested for its validity against the current gold standard ETDRS chart and is developed as an alternative to it for routine and research use.[9] Randomly generated optotypes to tackle the memorization effect of test takers was one of the significant advantages of COMPlog over conventional charts. The training- and technician-related errors are minimized with the help of standardized and controlled setup available with COMPlog. These facilities would aid to develop a new school eye screening protocol on the COMPlog platform so that schoolteachers, nurses, and other support staff can effectively contribute to the efforts to reduce the burden of avoidable blindness. In addition, the provision to automatically denote the visual acuity in any of the preferred acuity notations (decimal, Snellen fraction, logMAR, etc.) would potentially reduce scoring errors and subsequent false referrals observed generally with traditional acuity charts.[4] The scope of a typical screening protocol in school-going population was limited to visual acuity, refractive error, and squint assessment. On the other hand, the prevalence of ocular diseases such as trachoma (tropical), retinal, or corneal diseases is very low in the Indian population.[8] Thus, we did not include other less common ocular morbidities within the scope of this screening.

The refractive error was measured with photorefraction technique. Several studies have proved its efficacy in the screening for vision anomalies among larger population as it conveniently determines the refractive state together with accommodative response, pupil size, corneal reflexes, and interpupillary distance noninvasively.[1516171819] Screening of children in schools is most commonly carried out by trained schoolteachers or as a part of vision screening programs conducted by governmental or nongovernmental organizations with the help of eye care professionals. Primary vision screening through schoolteachers is an effective way to reduce the workload of optometrists and ophthalmologists but with a concern of associated errors in assessment and referral. The computerized and user-friendly screening devices (similar to COMPlog and photorefractor used in this study) would clearly enhance the effectiveness of the desired output even in the absence of trained professionals by providing rapid test outcome, lesser errors due to deviation in child concentration, noninvasive nature, and their proved reliability and validity. The feature of quick understanding with a shorter learning curve encourages the schoolteachers and vision technicians to use it at a primary level and decide for referral to an eye care professional without losing time.

Limitations

The exact underlying causes for the prevalence of visual impairment could not be reported in this study due to lack of time and workforce.

The internal factors such as the screen resolution and luminance level of COMPlog monitor have been preset before the study, but external factors such as level of classroom illumination were not uniform throughout the examination. This might have slightly influenced the accuracy of acuity measurement but within a desirable limit of a screening environment.

Conclusion

This study reported the prevalence of visual impairment to be 4.32% in the school-going population of Udupi district with higher prevalence from urban schools (15.3%) compared to rural schools (10.7%). Myopia was more prevalent (4.0%) than hyperopia (0.8%).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.