Prevalence Study of Visual Impairment and Blindness in Population of Mountainous Areas of Nepal

Research Article

J Community Med Health Care. 2017; 2(3): 1015.

Prevalence Study of Visual Impairment and Blindness in Population of Mountainous Areas of Nepal

Gurung KB¹*, Pandey S², Shrestha MK¹, Gurung R¹ and Ruit S¹

¹Tilganga Institute of Ophthalmology Nepal

²KIST Medical College and Teaching Hospital, Nepal

*Corresponding author: Gurung KB, Outreach Program Department, Tilganga Institute of Ophthalmology, Kathmandu, Nepal

Received: March 07, 2017; Accepted: April 21, 2017; Published: April 28, 2017

Abstract

Introduction: A population based cross sectional study was carried out with the aim of identifying the prevalence of visual impairment and blindness of the population living in those high altitude and mountainous regions.

Material and Methods: A population based cluster random sampling method was used to select study population of 2,050 individuals. A total of 41 clusters were selected by using a probability proportion to size sampling procedure. From each cluster, 50 individuals were randomly selected. An Ophthalmic Assistant conducted the interview and performed the eye examinations of respondents.

Results: A total of 1,945 respondents (95% response rate) were participated in the study. The blindness prevalence (Presenting Visual Acuity (PVA) in better eye <6/60) was found 0.77% (95% confidence interval (CI) 0.2-1.3), moderate visual impairment (PVA<6/18 to 6/60) 4.06% (95% CI 2-6.1) and mild visual impairment (PVA<6/9-6/18) was 12.85% (95% CI 9.3-16.4). A total of 63.8% of female respondents, 61.7% of illiterate and 79.8% respondents of 50 year and over had visual impairment of less than 6/18 and worse. The principle causes of visual impairment and blindness were uncorrected refractive error (54.8%) and cataract (40%) respectively.

Conclusion: The elderly, female and illiterate peoples were observed to be as the major risk factors for blindness and visual impairment. The uncorrected refractive error and cataract were found to be the major contributing factors of visual impairment and blindness. By developing screening and educational programs focused on the risk factors will reduce visual impairment and blindness.

Keywords: Blindness; Mountainous; Prevalence; Visual Impairment

Introduction

Nepal is considered a least developed country in the world with a low economic growth rate of less than 4% [1]. The country announced a constitution in 2015 after more than 15 years of an unstable political environment. Our country suffered a very strong earthquake in April 2015 [2]. The natural disaster added a further challenge for health, including eye health. In Nepal’s population of 28 million, over hundred thousand people are blind [3,4]. It is estimated that over 90% of the affected people reside in rural and remote areas, where often there is limited or no eye care service facilities [5]. Those, who are living in rural and remote areas of country, do not have adequate eye care services due to inaccessibility of such services. These factor may lead to visual impairment and blindness [6,7].

An increased emphasis has been put on the prevention and treatment of blindness and visual impairment around the world, but very little information is available on the prevalence of visual impairment and blindness and its causes in the highland population who live in the mountainous regions of Nepal, the Tibetan Plateau of China, Ladakh of India [8-11]. The high prevalence of blindness and visual impairment are found in high altitude areas such as Tibet in China and Karnali in Nepal where the prevalence of blindness was found to be 8.43% and 3.4% respectively [12,13].

Nepal is divided into three ecological regions i.e. Mountains, Hills and Terai (plain area). Out of 75 districts, Manang and Mustang Districts are known as the most remote and at the highest altitude of the inhabited mountainous districts in Nepal. Geographically both Districts fall between the altitudes of 1,000 to 8,100 meters above sea level and both of which are only accessible to their district Headquarters by road in the dry seasons and unpredictable air services. Furthermore, the social, economic and physical facilities are relatively sparse in both districts [3]. More than 95% of land is located at an altitude of above 3,000 meters above sea level [18,19]. An altitude of over 3,000 meters is well-known in medical literatures to cause biological effects on the human body. The atmospheric conditions in high mountainous regions are hypobaric with strong ultraviolet radiation and a high number of sunshine hours (average 3,400 hours per year) [20,21].

It is assessed that due to difficult geographical terrain, the population density is very low with limited access to eye health services, so people are prone to the risk of visual impairment and blindness in the mountainous areas of Nepal. To the best of our knowledge, no studies had been conducted in these two districts. Therefore, we conducted this study in Manang and Mustang which are known as high altitude mountainous districts. The main objective of the study was to find out the prevalence of visual impairment and blindness amongst the high altitude population of the mountainous regions of Nepal to enable the better future planning of eye health services.

Material and Methods

It was population based cross sectional study. The cluster random sampling method was applied to select the study populations from all age groups of two mountainous Districts (Manang and Mustang) in Nepal. The sample size was calculated by applying an estimated blindness prevalence of 2.6% (reference blindness prevalence of Gandaki stud) [22] in the sample size calculation formulae (Sample size, n = z2 * (p*q) /d2 Where, Z = Standard Normal Variant =2 for 95% confidence, P = prevalence rate, d= absolute error and design effect 2). By applying the reference prevalence of 2.6% in formulae, Sample size (n) = 4*(0.026*0.974)/0.01*0.01 = 1,013. The required sample size was calculated 1013. The design effect of 2 was used to select the most representative study population. After applying the design effect of 2 in the required sample size, the sample size was 2026 (sample size =1013*2 = 2026). According to Rapid Assessment of Avoidable Blindness (RAAB)’s recommendation, the proposed sample population was 50 individuals in each cluster. Thus, total sample population was taken 2,050 and the required cluster number was 41 (required cluster number (k) = 2026/50 = 41). The required Sampling Interval (SI) was 425 which was calculated by dividing total population of study districts by cluster number (SI=17,410/41=424.63=425). The study population was selected by applying the Probability Proportion to Size (PPS) sampling procedure.

Thus, 2,050 study populations (was 12% of the total population of two districts) and 41 clusters were selected from two districts. The Ward of Village Development Committee was taken as a cluster. In each cluster, the population was divided into segments of 425 people (425 was sampling interval). One segment was randomly selected from each cluster and 50 individuals were randomly selected as subject populations from the selected segment.

A semi-structured questionnaire and clinical performa for eye examination were used to collect data. The questionnaire and clinical performa that was used in earlier Rapid Assessment of Avoidable Blindness (RAAB) surveys was considered for this study. Those questionnaires and clinical performa was slightly modified and developed in the English language, but the questionnaire was translated into Nepalese language and tested again in a pilot test. The data collection was carried out from August to October in 2015. After completion of training of enumerator on data collection and data entry procedure, a pilot study was conducted in non-sampled population in one of study district.

During household survey by using the questionnaire, a trained Senior Ophthalmic Assistant conducted face to face interviews with the respondents of 18 year and over and with the guardians or parents of children less than 18 years. In the case of insufficient numbers of respondents in a study cluster, the required numbers of respondents were taken from adjoining clusters. After the interview, the respondents were invited to have an eye examination at a central point in the Village. The temporary eye clinic was set up at one of respondent’s house, a school building or a health post whichever was available. A trained eye health worker measured presenting and best corrected (pinhole) visual acuity of respondents of age of 5 years and older by using a standard Snellen vision chart at 6 meters distance. Children of 5 years and under, who could not take part in Snellen vision chart were tested by using a flash light and recorded as “Follows Light” (FL) or “does Not Follows Light” (NFL). A trained Senior Ophthalmic Assistant performed the eye examinations, including those of the anterior segment of the eyes of each respondent, by using flash light and portable slit lamp (Shin Nippon XL-1). The posterior segment of eyes was examined by using a direct ophthalmoscope (Heine) without and with dilation if necessary. Furthermore, the eye which didn’t improve to 6/12 with pinhole, except those with a cornea or an obvious cataract (defined as a lens opacity preventing view of the fundus), were dilated and evaluated for detailed evaluation of the posterior segment by using a direct ophthalmoscope. The suspected patient with posterior segment and other cases were referred to and examined by an Ophthalmologist based on a clinical examination history from an Ophthalmic Assistant at the District Headquarters during a surgical eye camp period. All eye examinations were carried out based on the study protocol.

In this study, four vision categories were used. They were defined as followings: a) normal vision: Presenting Visual Acuity (PVA) better than 6/12 in both eyes, b) mild visual impairment: PVA less than 6/9 to 6/18 in better eye, c) moderate visual impairment: PVA less than 6/18 to 6/60 in better eye, d) blindness: PVA less than 6/60 in better eye.

The collected quantitative data was entered into the developed online Google data base software. The data analysis was performed by using SPSS software version16.5 (SPSS Inc. Chicago, USA). P-value was calculated by using chi-square and fisher’s exact test. It was considered that p values <0.05 to denote statistical significance.

Out of 152 children of 5 years and below, 105 children, whose visual acuity could not be recorded with the Snellen vision chart, were excluded from the study. Because of the low number of respondents in the blindness and moderate visual impairment area age and sex adjusted analysis was not performed. Further, p value calculation was performed in the normal and visual impairment group.

The ethical approval of the study was permitted by the Institutional Review Committee of Tilganga Institute of Ophthalmology. The respondents, with the age of 18 years and older, had given written consent prior to the interview and eye examination, whilst with the children of less than 18 years old, were taken from their parents or guardian whoever was present.

Results

A total of 1,945 respondents (95% response rate) were included in the study of visual impairment and blindness. Male to female ratio was 1:1.39 in the study population. Total of 21% of respondents were from the less than 18 years age group, 45% of respondents from 18 to 49 years and rest were from 50 years and over age group. The mean age was 37.96 years (range: minimum 0.10 to maximum 92 years and Standard Deviation (SD) 21.85). Over 26% respondents were illiterate.

A total of 0.77% (95% Confidence Interval (CI) -0.2-1.3) respondents were blind in both eyes (in presenting visual acuity less than 6/60 in better eye), moderate visual impairment (PVA<6/18 to 6/60 in better eye) was 4.06% (95% CI 2-6.1) and mild visual impairment (PVA<6/9-6/18 in better eye) was 12.85% (95% CI 9.3- 16.4) in study population (Table 1). Total blind eyes were 2.19% (CI 95%, 1.2-3.2), moderate visually impaired eyes 5.40% (95% CI, 3.9- 6.9) and mild visually impaired eyes 14.19% (95% CI, 11.8-16.6) in study population (Table 1). Almost double of female respondents 66.7% (95% CI 61.5-71.8) were found to be blind and 63.3% (95% CI, 58.2-68.4) had moderate visual impairment as compared to their male counterpart. The mild visual impairment 56.8% (95% CI, 51.6- 62) was also observed higher in the female population than male.