Ophthalmic Epidemiology, 2014; 21(3): 190–196 ! Informa Healthcare USA, Inc. ISSN: 0928-6586 print / 1744-5086 online DOI: 10.3109/09286586.2014.906629
ORIGINAL ARTICLE
Prevalence of Visual Impairment and Blindness in Upper Egypt: A Gender-based Perspective Ahmed Mousa1, Paul Courtright2,3,4, Arminee Kazanjian3, and Ken Bassett4
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1
Department of Ophthalmology, College of Medicine, King Saud University, Riyadh, Saudi Arabia, 2Kilimanjaro Centre for Community Ophthalmology International, Division of Ophthalmology, University of Cape Town, Cape Town, South Africa, 3School of Population and Public Health, and 4British Columbia Centre for Epidemiologic and International Ophthalmology, University of British Columbia, Vancouver, Canada
ABSTRACT Purpose: To estimate the prevalence, causes of and risk factors for vision loss in Upper Egypt. Methods: In this cross-sectional study, four villages in Upper Egypt were randomly selected; within these four villages, households were randomly selected and within the selected households all residents aged 40 years were enumerated and enrolled. Door-to-door eye examinations of household members were conducted. Data on relevant demographic and socioeconomic characteristics were collected. The prevalence and causes of vision loss and associated risk factors were assessed. Sex differences in prevalence and determinants were also evaluated. Results: The prevalence of best eye presenting visual impairment, severe visual impairment, and blindness were 23.9%, 6.4%, and 9.3% respectively. The prevalence of blindness among women significantly exceeded that among men (11.8% vs. 5.4%, respectively, p = 0.021). The prevalence of cataract was 22.9% (higher in women, 26.5% than men 17.2%, p = 0.018). The prevalence of trachomatous trichiasis was 9.7% (higher among women, 12.5%, than men, 5.4%, p = 0.012). The principal causes of blindness were cataract (60%), uncorrected refractive errors (16%) and corneal opacities (12%). Age, sex, family size, illiteracy, unemployment, water source and sanitation methods and living conditions were the major risk factors for vision loss. Conclusion: The prevalence of visual impairment remains high in Egypt, particularly among women. Risk factors for blindness may differ between men and women. There is a need for qualitative investigations to better understand the causes behind the excess in prevalence of blindness among women. Keywords: Blindness, cataract, Egypt, gender, trichiasis, visual impairment
INTRODUCTION
Cataract surgical coverage (at VA56/60) in this population was only 13% and of those who had cataract surgery, only 9.4% were pseudophakic.1 A population-based study of trachoma which was conducted in the same governorate, estimated the prevalence of active trachoma (follicles and/or intense inflammation) among children (1–15 years) to be 36.5%. The prevalence of trachomatous trichiasis among adults (50 years and older) was 6.5%; with women being 1.68 times more likely to have trichiasis
Egypt’s first large-scale population-based survey of blindness (2002) estimated the prevalence of blindness (visual acuity, VA, 56/60) to be 7.9% and the prevalence of vision loss (VA56/18) to be 38.2% among adults aged 50 years and older in a Nile Delta governorate.1 The major causes of blindness were cataract or uncorrected aphakia (64.0%) and corneal opacities due to trachoma and other causes (30.2%).
Received 3 June 2013; Revised 26 January 2014; Accepted 12 February 2014; Published online 18 April 2014 Correspondence: Ahmed Mousa, PhD, Department of Ophthalmology, College of Medicine, King Saud University, PO Box 245 Riyadh, Saudi Arabia 11411. Tel: +966114786100. Fax: +96614775724. E-mail: [email protected]
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Prevalence of Low Vision and Blindness in Upper Egypt 191 (95% confidence interval, CI, 1.18–2.39) compared to men. Trichiasis was the second leading cause of both avoidable blindness (8%) and visual impairment (13.2%). Trichiasis surgical coverage was 34.4% while 44% of surgical cases had recurrent trichiasis.2 There is a paucity of population-based information on vision loss in Egypt. Egypt has a large population (83.7 million)3 and a relatively high ophthalmologist to population ratio (30 per million)4 yet there have been suggestions that blindness is high and coverage of cataract and trichiasis surgical services is low. We sought to assess the prevalence and causes of low vision and blindness as well as the associated risk factors in addition to the pattern of service use in four randomly selected villages in Samalout district, Menia Governorate, Upper Egypt, in preparation for an intervention study.
MATERIALS AND METHODS Menia Governorate, 243 km south of Cairo, stretches along the Nile and is 20 km wide and 120 km long. Menia consists of nine administrative districts with a total population of 4.2 million inhabitants. Samalout district is 30 km north of the capital, with 585,185 inhabitants living in 51 villages.4 At the governorate (Menia) and district (Samalout) levels, the Ministry of Health and Population provides surgical and tertiary eye care services through specialized eye hospitals in addition to a Department of Ophthalmology at the University Hospital in the city of Menia. Menia governorate has five ophthalmology hospitals, one of which is in Samalout city. Additionally, there are a number of ophthalmology departments in general, private and nongovernmental organization hospitals with around 19 working ophthalmologists serving the governorate. We conducted the current study between March 2007 and September 2008. Among Samalout’s 51 villages, 31 were both large enough (population size 45000 inhabitants) and had good access to village health units and a tertiary eye care facility. Among these 31 villages, four were randomly selected for inclusion in this cross-sectional survey using probability proportional to size (PPS). The total population of the four selected villages was 49,017.3 In the second sampling stage, a specific sample was calculated for each village, as per the total village population aged 40 years and older, where systematic random sampling (using random walk) was applied to select and recruit households. Essential data for sampling calculations were size of the target population (using the Egyptian population census 2006),5 estimated prevalence of disease (using an unpublished 2002 Menia survey), power (1- = 80%), type I error ( = 0.05), and corresponding CIs of 95%, according to the standard World Health Organization (WHO) manual for health !
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surveys.6 Calculated samples ranged from 112 to 147 in the four villages (due to differences in population size). A fixed sample size was set at 150 subjects aged 40 years and older for each village, where age and residency were the only inclusion criteria for this study. Each village was further divided into two major sectors according to distribution of the population and households using a recent village map. A central household was randomly selected at the middle of each sector as a starting point, and then every fifth household was visited until the total sample size was achieved. Two teams conducted the survey, each consisting of an ophthalmologist, two nurses, one local health worker and a local coordinator. Before starting the field work, two training sessions were held for the survey staff. The training included ‘‘conduct of standardized eye examination procedure,’’ ‘‘adherence to study protocol standards,’’ and ‘‘guidelines for completing questionnaires.’’ After listing and enumeration of the selected households, the team was introduced to the selected household heads by the local guide and oral informed consent was requested from the household head. This was followed by a short interview to collect relevant demographic and socioeconomic data as well as history of previous eye surgeries (if any) from the eligible subjects by the trained nurses. After completion of basic data sheets, nurses assessed VA using the WHO shortened Snellen ‘‘E’’ optotype chart. Assessment of vision was carried out in a suitable outdoor area with sufficient natural light, starting at 6 m. Participants had to correctly identify at least four of the five optotypes (or three of four, etc.) before they were given a score for the optotype VA level. Subjects with VA56/18 in either eye had vision retested in that eye with pinhole to assess best-corrected vision. If vision was 56/60, further testing was done at 3 m, then 1 m; if still unable to see at that distance the eye was assessed either as light perception or no light perception. For analytic purposes the WHO criteria were used: best eye presenting vision 53/60 (defined as blindness), 3/60 to 56/60 (severe visual impairment), and 6/60 to 56/18 (visual impairment). Vision loss was defined as all of these combined; i.e. best eye presenting vision 56/18. Ophthalmologists conducted a detailed eye examination to determine the existence of trichiasis (or evidence of epilation) and identify the major cause of vision loss using a torch, direct and indirect ophthalmoscopes (whenever indicated). Individuals with cataract (causing vision 56/18) and/or trichiasis or individuals who had received previous services underwent an additional interview on service use. Those in need of further investigation, medical or surgical services were referred to Samalout and Menia Eye Hospitals according to prior arrangements with the local health authorities.
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192 A. Mousa et al. Data were reviewed for accuracy and stored in a specifically designed database using Microsoft Access 2007. Data analysis was performed using SPSS version 19.0 (IBM Inc, Chicago, IL, USA), MedCalc 11.6 (MedCalc Software, Ostend, Belgium) and StatsDirect statistical software, version 2.7.2 (StatsDirect Ltd, Cheshire, UK). Analyses included prevalence estimates and frequency of causes of low vision and blindness where individuals were set as the unit of analysis. Univariate and multivariate (binary logistic regression) analyses were used to investigate associations between potential demographic and socioeconomic risk factors and vision loss. Ethical approval was obtained from the University of British Columbia Behavioral Research Ethics Board, Office of Research Services in March 2006 and from local health authorities in Egypt (Approval #H06-80425 Gender and Blindness – Egypt).
RESULTS Among the target sample of 600 subjects aged 40 years and older, 525 (87.5%) were examined in 272 households. Among 75 subjects not examined, 53 (70.7%) were not available after repeated visits, 15 (20%) could not be assessed (four of them because of age and illness), while seven (9.3%) refused to be examined. Among the 53 people not available, 21 (39.6%) were men. The prevalence of visual impairment was 23.9% (95% CI 20.2–27.6%), severe visual impairment was 6.4% (95% CI 4.3–8.6%), and blindness was 9.3% (95% CI 6.8–11.8%). Female- exceeded male-specific prevalence in all vision loss categories, however, the difference was only statistically significant for the blind group (11.8% vs 5.4%, respectively, p = 0.021; Table 1). The prevalence of cataract (defined as cloudiness or opacity in the normally transparent crystalline lens of an eye with VA56/18) was 22.9% (95% CI 19.3– 26.5%, where female prevalence (26.5%) significantly exceeded male prevalence (17.2%; p = 0.0.018). The prevalence of trachomatous trichiasis (defined as one or more lashes touching the eyeball or evidence of epilation, with or without corneal scarring) was
TABLE 1. Prevalence of best eye presenting vision loss in Menia, Egypt. Visual acuity
Males n (%)
Females n (%)
Total n (%)
Normal (visual acuity 6/18) 137 (67.8) 174 (55.6) 311 (60.4) Visual impairment 45 (22.3) 78 (24.9) 123 (23.9) (visual acuity 56/18–6/60) Severe visual impairment 9 (4.5) 24 (7.7) 33 (6.4) (visual acuity 56/60–3/60) Blind (visual acuity 53/60) 11 (5.4) 37 (11.8) 48 (9.3) Missing 2 8 10 Total 204 321 525
9.7% (95% CI 7.2–12.3%), where female prevalence (12.5%) significantly exceeded male prevalence (5.4%; p = 0.012; Table 2). The principal causes of visual impairment and severe visual impairment were cataract (53.7%), uncorrected refractive error (32.5%), trachomatous corneal opacity (3.8%), retinal detachment (1.3%), and others (8.7%). The principal causes of blindness were cataract (60%) uncorrected refractive error (16%), trachomatous corneal opacity (12%), other corneal opacities (8%), in addition to some other minor causes (4%; Figure 1). Cataract surgical coverage (defined as operated patients divided by operated plus un-operated patients at VA56/18) was 18.9% (28/148), which was relatively low among both women (16.7%, 17/ 102) and men (23.9%, 11/46), where the difference was not statistically significant (p = 0.419). Among the 17 women and 11 men who had cataract surgery; six women and three men had aphakic cataract surgery (9/28, 32.1% overall). Trichiasis surgical coverage was 22.7% (15/66); the coverage among women was insignificantly lower (16.7%, 8/48) than among men (38.9%, 7/18; p = 0.113). Among those who had had surgery, the recurrence rate of trichiasis was 53.3% (8/15; five women and three men). Multivariate adjustment using binary logistic regression analysis showed numerous independent risk factors associated with vision loss (best eye, presenting vision56/18; Table 3). Conduct of logistic regression analysis among women revealed that female-specific risk factors were marital status (single, p = 0.02), education (can read and write, p50.001; primary school level, p50.001; preparatory school level, p50.02), sex of household head (female, p50.001), children sleeping on separate pillows (no, p50.001), water source (general village tap, p50.001), uncovered toilet (p50.001), absence of washroom tap (p = 0.005), method of disposing garbage (use as fertilizer, p = 0.004), absence of separate kitchen (p50.001), animals in house (evidence of cattle dirtiness, p50.001), and no source of income (p = 0.004; Table 4). TABLE 2. Prevalence of cataract and trachomatous trichiasis in Menia, Egypt. Cause Cataract Unilateral Bilateral Total Trachomatous trichiasis Unilateral Bilateral Total
Males n (%)
Females n (%)
Total n (%)
7 (20)a 28 (80)a 35 (17.2)b
22 (25.9)a 63 (74.1)a 85 (26.5)b
29 (24.2)a 91 (75.8)a 120 (22.9)b
3 (27.3)a 8 (72.7)a 11 (5.4)b
13 (32.5)a 27 (67.5)a 40 (12.5)b
16 (31.4)a 35 (68.6)a 51 (9.7)b
Percentage is of column total. bPercentage is of sample total.
a
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Prevalence of Low Vision and Blindness in Upper Egypt 193
FIGURE 1. Major causes of blindness in Menia, Egypt.
TABLE 3. Adjusted odds ratios (logistic regression adjusting for all other factors) of risk factors for vision loss (visual acuity 56/18) in the total sample, Menia, Egypt. Characteristic
Category
Age Sex Marital status Occupation Education Household head Number of children per household Water source Method of sanitation Latrine Washroom Method of garbage disposal
Presence of animals Household construction material
Main source of income
n (%)
Female Widowed Farmer Unemployed Illiterate Age
321 109 392 87 269
(61.1) (20.7) (74.8) (16.5) (51.2)
Pump Well Tank inside No sanitation Evacuate 56 month Washroom no door Toilet not covered Burn Throw out Enclosure in house Mud Wood Stone Temporarily hired
91 8 325 81 22 25 112 79 122 224 139 13 59 241
(17.3) (1.6) (61.8) (15.5) (4.2) (4.8) (21.3) (15.1) (23.3) (42.7) (26.4) (2.4) (11.3) (45.9)
Adjusted OR
95% CI
1.1 2.5 14.4 1.7 1.8 3.8 1.03 1.1 4.9 3.8 3.8 7.4 1.02 2.9 2.2 3.4 12.4 7.7 5.03 2.04 1.9 4.8
(1.05–1.13) (1.57–4.26) (3.78–54.64) (1.25–5.34) (1.06–8.33) (1.9–7.5) (1.01–1.05) (1.09–1.34) (1.35–17.54) (1.58–9.05) (1.32–11.09) (1.81–30.26) (1.01–1.04) (1.17–7.18) (1.10–4.51) (1.19–9.51) (4.61–33.31) (2.31–12.17) (2.48–7.19) (1.64–7.28) (1.38–2.63) (1.26–18.14)
Reference group for each category: Sex, male; Marital status, divorced; Occupation, other; Education, postgraduate; Water source, general network; Sanitation, general network; Latrine, evacuate every 5 years; Washroom door, present; Toilet covered, yes; Garbage collection, collecting car; Animal enclosure in house, no; Household construction material,
DISCUSSION The prevalence of vision loss in Egypt has been reported since the early 1970s as relatively high.1,2,7–9 Similar to previous work in Egypt, we detected a high !
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prevalence of vision loss among the target population (unadjusted for clustering due to the small number of clusters) as well as low coverage of cataract and trichiasis surgical services, regardless of the high ratio of ophthalmologists to population in the governorate (&1:200,000). This high prevalence confirms previous
194 A. Mousa et al. TABLE 4. Adjusted odds ratios (logistic regression) of female-specific risk factors for vision loss (visual acuity56/18) in Menia, Egypt. Characteristic Marital status Occupation Education
Household head
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Number of children per household Children sleeping on the same pillow Water source
Sanitation method Washroom Method of garbage disposal
Existence of separate kitchen Presence of animals Household construction material
Source of income
Category
n (%)
Widowed Single Farmer Unemployed Illiterate Read and write Primary school Preparatory school Age Sex (female)
102 13 243 72 211 48 22 13
No separate pillow Pump Well General village tap Tank inside No sanitation Uncovered toilet Bathroom no taps Burn Fertilizer Throw out No Enclosure in house Animal dirt in house Mud Wood Stone No source of income
106 53 6 27 201 49 167 60 46 64 75 170 135 71 30 7 40 46
(31.9) (3.9) (75.7) (22.4) (65.7) (14.9) (6.9) (4)
117 (36.5) (32.9) (16.4) (2) (8.6) (62.5) (15.1) (54.9) (18.8) (14.5) (20.1) (23.4) (53) (42.1) (22) (9.2) (2.3) (12.5) (14.5)
Adjusted OR
95% CI
16.2 3.1 13.8 1.5 2.2 1.6 1.3 1.2 1.3 6.1 3.5 2.2 7.5 5.6 1.9 2.9 5.1 1.5 3.4 3.1 4.4 4.8 6.6 9.7 9.1 5.8 1.9 3.6 15.1
(2.51–52.73) (1.89–11.41) (7.21–18.65) (1.16–1.76) (1.03–3.69) (1.01–1.93) (1.21–1.68) (1.14–1.84) (1.18–5.01) (2.26–16.37) (1.82–6.42) (1.21–4.35) (1.27–14.56) (2.71–7.85) (1.23–5.32) (1.69–7.48) (2.18–9.49) (1.16–4.15) (1.87–21.11) (2.71–9.21) (2.28–13.57) (2.09–8.38) (1.61–9.42) (3.76–15.21) (4.48–14.74) (3.73–9.92) (1.16–5.31) (1.89–7.15) (2.82–29.24)
Reference group for each category: Marital status, divorced; Occupation, other; Education, postgraduate; Household head sex, male; Sleeping on separate pillow, yes; Water source, general network; Sanitation, general network; Toilet covered, yes; Bathroom tap, present; Garbage collection, collecting car; Separate kitchen, yes; Animal enclosure in house, no; Animal dirt, absent; Household construction material, others; Source of income, permanent job. CI, confidence interval; OR, odds ratio
findings in the literature and is similar to findings from Sudan (11%), however it is much higher than that of Libya (3.3%) and Saudi Arabia (2.6%).10,11 Additionally, our findings show that the major causes of visual impairment are more or less the same as in similar developing countries, i.e. cataract (53.7%) and uncorrected refractive errors (32.5%). Worldwide, women bear approximately two-thirds of the burden of severe visual impairment and blindness,13,14 the main reason being lower service use, especially in developing countries.11,14–16 In the current study we also detected a higher prevalence of vision loss in women compared to men (blindness 11.8% versus 5.4%; visual impairment 32.6% versus 26.8%, respectively). Regionally, Khandekar and co-authors, Al Gamra and co-authors, and Chiang and co-authors reported similar excess visual impairment and blindness among women compared to men in Oman, Qatar, and Palestine, respectively.17–19 Women had a slightly higher age-adjusted incidence of cataract compared to men, but this biological difference was small compared to the large difference in (age-adjusted) prevalence between men and
women.20 Globally, women account for 65% of cataract blindness because they are less likely to receive cataract surgery than men and they tend to seek surgery later. In some settings women have poorer surgical outcomes which can contribute to gender-specific barriers and attitudes towards service use.1,2 Women account for about two-thirds of the global burden of trachomatous trichiasis and the subsequent blindness due to corneal scarring. Although the prevalence of active disease is usually similar for boys and girls, adult women tend to have more active disease than adult men.21,22 This is probably due to their higher frequency of interaction with children.23 Recent reports show that trachoma is declining in many endemic countries. Prevention of trachoma and control of its ocular complications can be achieved through surgery to correct trichiasis, antibiotics to treat active disease, face washing and environmental improvements to reduce transmission.24–26 As yet, trachoma has not been mapped in Egypt and specific interventions are quite limited and it is likely that trachoma remains a public health problem in Menia and other selected governorates in Egypt. Ophthalmic Epidemiology
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Prevalence of Low Vision and Blindness in Upper Egypt 195 Recent epidemiologic studies have begun estimating female-specific risk factors for blindness.27 Our analysis found several female-specific risk factors for blindness that were not significant for the whole sample but were significant for women alone: being single, education ‘‘read and write,’’ ‘‘primary’’ and ‘‘preparatory’’ school levels, household head ‘‘female’’, ‘‘children sleeping on the same pillow’’, water source ‘‘general village tap’’, uncovered toilet, absence of washroom tap, using garbage as fertilizers, absence of kitchen, presence of cattle dirt, and having no source of income. Female-specific social determinants were associated with characteristics of the individual (education and source of income) as well as characteristics of the day-to-day activities that women undertake in rural areas (for example collecting water from the village tap, preparing fertilizers for cultivation, and so on). Having education and a permanent source of income generally empowers women in decision making within the household and community; conversely, women without education and a stable source of income have been shown to have less decision-making capacity related to use of eye care services compared to men.28 Poor hygienic and economic conditions are generally a reflection of reduced socioeconomic status which is well-recognized as a risk factor for blindness and use of eye care services.29 None of these factors are easily amenable to change. Egypt has sufficient clinical capacity to restore vision to most of those with vision loss (among whom almost two-thirds are women). According to an Egyptian Ophthalmologic Society report (2005), there are around 4000 Egyptian ophthalmologists, 40% of whom are registered as eye surgeons. Most ophthalmologists (including surgeons) congregate in urban areas; rural populations seldom use30 these services, even if these services are provided free of charge.31 Previous research has shown a high proportion of poor outcomes of cataract and trichiasis surgical services1,2 which would need to be addressed to improve uptake. The challenge, therefore, is linking populations in need with good-quality clinical services. The current study has a number of limitations including the relatively small sample size and the slightly higher number of un-examined men compared to un-examined women due to their availability during household examinations. It is possible that those who could not be examined due to their absence on examination days could have VA findings different to the examined population. Findings from a separate multivariate risk factor assessment model for men were not informative, being similar to those of the combined risk factor assessment. Previous research in the Nile Delta
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illustrated some of the sociocultural impediments that women face.32 Qualitative research is needed to better understand of how to address the barriers that women face to use of existing eye care services. In conclusion, the prevalence of low vision and blindness remains high in Egypt, particularly among women. Our data suggest that female-specific risk factors for vision loss relate to both sociodemographic as well as environmental factors, and that use of services is very low. A major national effort may be needed in order for Egypt to reach its VISION 2020 target.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. The authors acknowledge the outstanding support from the Canadian Institute for Health Research (CIHR), The British Columbia Centre for Epidemiologic and International Ophthalmology, University of British Columbia as well as the technical support of Ms Priscilla Gikandi, Assistant Researcher, Research Unit, Department of Ophthalmology, King Saud University.
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196 A. Mousa et al. 9. Courtright P, Sheppard J, Schachter J, et al. Trachoma and blindness in the Nile Delta: current patterns and projections for the future in the rural Egyptian population. Br J Ophthalmol 1989;73(7):536–540. 10. Al Ghamdi AH, Rabiu M, Hajar S, et al. Rapid assessment of avoidable blindness and diabetic retinopathy in Taif, Saudi Arabia. Br J Ophthalmol 2012;96(9):1168–1172. 11. Rabiu MM, Jenf M, Fituri S, et al. Prevalence and causes of visual impairment and blindness, cataract surgical coverage and outcomes of cataract surgery in Libya. Ophthalmic Epidemiol 2013;20(1):26–32. 12. Abou-Gareeb I, Lewallen S, Bassett K, Courtright P. Gender and blindness: a meta-analysis of populationbased prevalence surveys. Ophthalmic Epidemiol 2001; 8(1):39–56. 13. Courtright P, Abou-Gareeb I, Lewallen S, Bassett K. Gender and blindness. In: Gender health. Geneva: World Health Organization, Department of Gender and Women’s Health; 2001. 14. Courtright P, Bassett KL. Gender and blindness: eye disease and the use of eye care services. Community Eye Health 2003;16:11–12. 15. Lewallen S, Courtright P. Gender and use of cataract surgical services in developing countries. Bull WHO 2002:300–303. 16. Lewallen S, Mousa A, Bassett K, Courtright P. Cataract surgical coverage remains lower in women. Br J Ophthalmol 2009;93(3):295–298. 17. Al Gamra H, Al Mansouri F, Khandekar R, et al. Prevalence and causes of blindness, low vision and status of cataract in 50 years and older citizen of Qatar – a community based survey. Ophthalmic Epidemiol 2010;17(5):292–300. 18. Chiang F, Kuper H, Lindfield R, et al. Rapid assessment of avoidable blindness in the Occupied Palestinian Territories. PLoS One 2010;5(7):e11854. 19. Khandekar R, Mohammed AJ. Gender inequality in vision loss and eye diseases: evidence from the Sultanate of Oman. Indian J Ophthalmol 2009;57(6):443–449. 20. West SK, Valmadrid CT. Epidemiology of risk factors for age-related cataract. Surv Ophthalmol 1995;39(4):323–334. 21. Courtright P, West SK. Contribution of sex-linked biology and gender roles to disparities with trachoma. Emerg Infect Dis 2004;10(11):2012–2016.
22. Cromwell EA, Courtright P, King JD, et al. The excess burden of trachomatous trichiasis in women: a systematic review and meta-analysis. Trans R Soc Trop Med Hyg 2009; 103(10):985–992. 23. Wolfson EM, Fedewa L, Young SA. Trachoma: a woman s health issue. The Global Alliance for Women s Health [Internet]. (1997) [updated 1999; cited 2014 April 10, 2014]. Available from: http://www.gawh.org/publications/ trach-e.pdf. 24. Emerson PM, Lindsay SW, Walraven GE, et al. Effect of fly control on trachoma and diarrhoea. Lancet 1999; 353(9162):1401–1403. 25. West SK, Congdon N, Katala S, Mele L. Facial cleanliness and risk of trachoma in families. Arch Ophthalmol 1991; 109(6):855–857. 26. Khandekar R, Al Harthy H, Al Harby S, et al. Oman’s progress towards reaching ‘‘Ultimate Intervention Goals’’ for the surgery ‘‘S’’ component of SAFE strategy for the elimination of blinding trachoma in 2008. Ophthalmic Epidemiol 2010;17(6):360–365. 27. Ulldemolins AR, Lansingh VC, Valencia LG, et al. Social inequalities in blindness and visual impairment: a review of social determinants. Indian J Ophthalmol 2012;60(5): 368–375. 28. Mwende J, Bronsard A, Mosha M, et al. Delay in presentation to hospital for surgery for congenital and developmental cataract in Tanzania. Br J Ophthalmol 2005;89(11): 1478–1482. 29. Gilbert CE, Shah SP, Jadoon MZ, et al. Poverty and blindness in Pakistan: results from the Pakistan national blindness and visual impairment survey. BMJ 2008; 336(7634):29–32. 30. The American Academy of Ophthalmology, International Society Listing [Internet]. 2014 [updated March 15, 2013; cited April 10, 2014]. Available from: http:// www.aao.org/international/professional/intl_soc_listing. cfm?fuseaction=detail&id=000000789788. 31. Nirmalan PK, Katz J, Robin AL, et al. Utilisation of eye care services in rural south India: the Aravind Comprehensive Eye Survey. Br J Ophthalmol 2004;88(10):1237–1241. 32. Lane SD, Mikhail BI, Reizian A, et al. Sociocultural aspects of blindness in an Egyptian delta hamlet: visual impairment vs. visual disability. Med Anthropol 1993;15(3): 245–260.
Ophthalmic Epidemiology
ORIGINAL ARTICLE
Prevalence of Visual Impairment and Blindness in Upper Egypt: A Gender-based Perspective Ahmed Mousa1, Paul Courtright2,3,4, Arminee Kazanjian3, and Ken Bassett4
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1
Department of Ophthalmology, College of Medicine, King Saud University, Riyadh, Saudi Arabia, 2Kilimanjaro Centre for Community Ophthalmology International, Division of Ophthalmology, University of Cape Town, Cape Town, South Africa, 3School of Population and Public Health, and 4British Columbia Centre for Epidemiologic and International Ophthalmology, University of British Columbia, Vancouver, Canada
ABSTRACT Purpose: To estimate the prevalence, causes of and risk factors for vision loss in Upper Egypt. Methods: In this cross-sectional study, four villages in Upper Egypt were randomly selected; within these four villages, households were randomly selected and within the selected households all residents aged 40 years were enumerated and enrolled. Door-to-door eye examinations of household members were conducted. Data on relevant demographic and socioeconomic characteristics were collected. The prevalence and causes of vision loss and associated risk factors were assessed. Sex differences in prevalence and determinants were also evaluated. Results: The prevalence of best eye presenting visual impairment, severe visual impairment, and blindness were 23.9%, 6.4%, and 9.3% respectively. The prevalence of blindness among women significantly exceeded that among men (11.8% vs. 5.4%, respectively, p = 0.021). The prevalence of cataract was 22.9% (higher in women, 26.5% than men 17.2%, p = 0.018). The prevalence of trachomatous trichiasis was 9.7% (higher among women, 12.5%, than men, 5.4%, p = 0.012). The principal causes of blindness were cataract (60%), uncorrected refractive errors (16%) and corneal opacities (12%). Age, sex, family size, illiteracy, unemployment, water source and sanitation methods and living conditions were the major risk factors for vision loss. Conclusion: The prevalence of visual impairment remains high in Egypt, particularly among women. Risk factors for blindness may differ between men and women. There is a need for qualitative investigations to better understand the causes behind the excess in prevalence of blindness among women. Keywords: Blindness, cataract, Egypt, gender, trichiasis, visual impairment
INTRODUCTION
Cataract surgical coverage (at VA56/60) in this population was only 13% and of those who had cataract surgery, only 9.4% were pseudophakic.1 A population-based study of trachoma which was conducted in the same governorate, estimated the prevalence of active trachoma (follicles and/or intense inflammation) among children (1–15 years) to be 36.5%. The prevalence of trachomatous trichiasis among adults (50 years and older) was 6.5%; with women being 1.68 times more likely to have trichiasis
Egypt’s first large-scale population-based survey of blindness (2002) estimated the prevalence of blindness (visual acuity, VA, 56/60) to be 7.9% and the prevalence of vision loss (VA56/18) to be 38.2% among adults aged 50 years and older in a Nile Delta governorate.1 The major causes of blindness were cataract or uncorrected aphakia (64.0%) and corneal opacities due to trachoma and other causes (30.2%).
Received 3 June 2013; Revised 26 January 2014; Accepted 12 February 2014; Published online 18 April 2014 Correspondence: Ahmed Mousa, PhD, Department of Ophthalmology, College of Medicine, King Saud University, PO Box 245 Riyadh, Saudi Arabia 11411. Tel: +966114786100. Fax: +96614775724. E-mail: [email protected]
190
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Prevalence of Low Vision and Blindness in Upper Egypt 191 (95% confidence interval, CI, 1.18–2.39) compared to men. Trichiasis was the second leading cause of both avoidable blindness (8%) and visual impairment (13.2%). Trichiasis surgical coverage was 34.4% while 44% of surgical cases had recurrent trichiasis.2 There is a paucity of population-based information on vision loss in Egypt. Egypt has a large population (83.7 million)3 and a relatively high ophthalmologist to population ratio (30 per million)4 yet there have been suggestions that blindness is high and coverage of cataract and trichiasis surgical services is low. We sought to assess the prevalence and causes of low vision and blindness as well as the associated risk factors in addition to the pattern of service use in four randomly selected villages in Samalout district, Menia Governorate, Upper Egypt, in preparation for an intervention study.
MATERIALS AND METHODS Menia Governorate, 243 km south of Cairo, stretches along the Nile and is 20 km wide and 120 km long. Menia consists of nine administrative districts with a total population of 4.2 million inhabitants. Samalout district is 30 km north of the capital, with 585,185 inhabitants living in 51 villages.4 At the governorate (Menia) and district (Samalout) levels, the Ministry of Health and Population provides surgical and tertiary eye care services through specialized eye hospitals in addition to a Department of Ophthalmology at the University Hospital in the city of Menia. Menia governorate has five ophthalmology hospitals, one of which is in Samalout city. Additionally, there are a number of ophthalmology departments in general, private and nongovernmental organization hospitals with around 19 working ophthalmologists serving the governorate. We conducted the current study between March 2007 and September 2008. Among Samalout’s 51 villages, 31 were both large enough (population size 45000 inhabitants) and had good access to village health units and a tertiary eye care facility. Among these 31 villages, four were randomly selected for inclusion in this cross-sectional survey using probability proportional to size (PPS). The total population of the four selected villages was 49,017.3 In the second sampling stage, a specific sample was calculated for each village, as per the total village population aged 40 years and older, where systematic random sampling (using random walk) was applied to select and recruit households. Essential data for sampling calculations were size of the target population (using the Egyptian population census 2006),5 estimated prevalence of disease (using an unpublished 2002 Menia survey), power (1- = 80%), type I error ( = 0.05), and corresponding CIs of 95%, according to the standard World Health Organization (WHO) manual for health !
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surveys.6 Calculated samples ranged from 112 to 147 in the four villages (due to differences in population size). A fixed sample size was set at 150 subjects aged 40 years and older for each village, where age and residency were the only inclusion criteria for this study. Each village was further divided into two major sectors according to distribution of the population and households using a recent village map. A central household was randomly selected at the middle of each sector as a starting point, and then every fifth household was visited until the total sample size was achieved. Two teams conducted the survey, each consisting of an ophthalmologist, two nurses, one local health worker and a local coordinator. Before starting the field work, two training sessions were held for the survey staff. The training included ‘‘conduct of standardized eye examination procedure,’’ ‘‘adherence to study protocol standards,’’ and ‘‘guidelines for completing questionnaires.’’ After listing and enumeration of the selected households, the team was introduced to the selected household heads by the local guide and oral informed consent was requested from the household head. This was followed by a short interview to collect relevant demographic and socioeconomic data as well as history of previous eye surgeries (if any) from the eligible subjects by the trained nurses. After completion of basic data sheets, nurses assessed VA using the WHO shortened Snellen ‘‘E’’ optotype chart. Assessment of vision was carried out in a suitable outdoor area with sufficient natural light, starting at 6 m. Participants had to correctly identify at least four of the five optotypes (or three of four, etc.) before they were given a score for the optotype VA level. Subjects with VA56/18 in either eye had vision retested in that eye with pinhole to assess best-corrected vision. If vision was 56/60, further testing was done at 3 m, then 1 m; if still unable to see at that distance the eye was assessed either as light perception or no light perception. For analytic purposes the WHO criteria were used: best eye presenting vision 53/60 (defined as blindness), 3/60 to 56/60 (severe visual impairment), and 6/60 to 56/18 (visual impairment). Vision loss was defined as all of these combined; i.e. best eye presenting vision 56/18. Ophthalmologists conducted a detailed eye examination to determine the existence of trichiasis (or evidence of epilation) and identify the major cause of vision loss using a torch, direct and indirect ophthalmoscopes (whenever indicated). Individuals with cataract (causing vision 56/18) and/or trichiasis or individuals who had received previous services underwent an additional interview on service use. Those in need of further investigation, medical or surgical services were referred to Samalout and Menia Eye Hospitals according to prior arrangements with the local health authorities.
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192 A. Mousa et al. Data were reviewed for accuracy and stored in a specifically designed database using Microsoft Access 2007. Data analysis was performed using SPSS version 19.0 (IBM Inc, Chicago, IL, USA), MedCalc 11.6 (MedCalc Software, Ostend, Belgium) and StatsDirect statistical software, version 2.7.2 (StatsDirect Ltd, Cheshire, UK). Analyses included prevalence estimates and frequency of causes of low vision and blindness where individuals were set as the unit of analysis. Univariate and multivariate (binary logistic regression) analyses were used to investigate associations between potential demographic and socioeconomic risk factors and vision loss. Ethical approval was obtained from the University of British Columbia Behavioral Research Ethics Board, Office of Research Services in March 2006 and from local health authorities in Egypt (Approval #H06-80425 Gender and Blindness – Egypt).
RESULTS Among the target sample of 600 subjects aged 40 years and older, 525 (87.5%) were examined in 272 households. Among 75 subjects not examined, 53 (70.7%) were not available after repeated visits, 15 (20%) could not be assessed (four of them because of age and illness), while seven (9.3%) refused to be examined. Among the 53 people not available, 21 (39.6%) were men. The prevalence of visual impairment was 23.9% (95% CI 20.2–27.6%), severe visual impairment was 6.4% (95% CI 4.3–8.6%), and blindness was 9.3% (95% CI 6.8–11.8%). Female- exceeded male-specific prevalence in all vision loss categories, however, the difference was only statistically significant for the blind group (11.8% vs 5.4%, respectively, p = 0.021; Table 1). The prevalence of cataract (defined as cloudiness or opacity in the normally transparent crystalline lens of an eye with VA56/18) was 22.9% (95% CI 19.3– 26.5%, where female prevalence (26.5%) significantly exceeded male prevalence (17.2%; p = 0.0.018). The prevalence of trachomatous trichiasis (defined as one or more lashes touching the eyeball or evidence of epilation, with or without corneal scarring) was
TABLE 1. Prevalence of best eye presenting vision loss in Menia, Egypt. Visual acuity
Males n (%)
Females n (%)
Total n (%)
Normal (visual acuity 6/18) 137 (67.8) 174 (55.6) 311 (60.4) Visual impairment 45 (22.3) 78 (24.9) 123 (23.9) (visual acuity 56/18–6/60) Severe visual impairment 9 (4.5) 24 (7.7) 33 (6.4) (visual acuity 56/60–3/60) Blind (visual acuity 53/60) 11 (5.4) 37 (11.8) 48 (9.3) Missing 2 8 10 Total 204 321 525
9.7% (95% CI 7.2–12.3%), where female prevalence (12.5%) significantly exceeded male prevalence (5.4%; p = 0.012; Table 2). The principal causes of visual impairment and severe visual impairment were cataract (53.7%), uncorrected refractive error (32.5%), trachomatous corneal opacity (3.8%), retinal detachment (1.3%), and others (8.7%). The principal causes of blindness were cataract (60%) uncorrected refractive error (16%), trachomatous corneal opacity (12%), other corneal opacities (8%), in addition to some other minor causes (4%; Figure 1). Cataract surgical coverage (defined as operated patients divided by operated plus un-operated patients at VA56/18) was 18.9% (28/148), which was relatively low among both women (16.7%, 17/ 102) and men (23.9%, 11/46), where the difference was not statistically significant (p = 0.419). Among the 17 women and 11 men who had cataract surgery; six women and three men had aphakic cataract surgery (9/28, 32.1% overall). Trichiasis surgical coverage was 22.7% (15/66); the coverage among women was insignificantly lower (16.7%, 8/48) than among men (38.9%, 7/18; p = 0.113). Among those who had had surgery, the recurrence rate of trichiasis was 53.3% (8/15; five women and three men). Multivariate adjustment using binary logistic regression analysis showed numerous independent risk factors associated with vision loss (best eye, presenting vision56/18; Table 3). Conduct of logistic regression analysis among women revealed that female-specific risk factors were marital status (single, p = 0.02), education (can read and write, p50.001; primary school level, p50.001; preparatory school level, p50.02), sex of household head (female, p50.001), children sleeping on separate pillows (no, p50.001), water source (general village tap, p50.001), uncovered toilet (p50.001), absence of washroom tap (p = 0.005), method of disposing garbage (use as fertilizer, p = 0.004), absence of separate kitchen (p50.001), animals in house (evidence of cattle dirtiness, p50.001), and no source of income (p = 0.004; Table 4). TABLE 2. Prevalence of cataract and trachomatous trichiasis in Menia, Egypt. Cause Cataract Unilateral Bilateral Total Trachomatous trichiasis Unilateral Bilateral Total
Males n (%)
Females n (%)
Total n (%)
7 (20)a 28 (80)a 35 (17.2)b
22 (25.9)a 63 (74.1)a 85 (26.5)b
29 (24.2)a 91 (75.8)a 120 (22.9)b
3 (27.3)a 8 (72.7)a 11 (5.4)b
13 (32.5)a 27 (67.5)a 40 (12.5)b
16 (31.4)a 35 (68.6)a 51 (9.7)b
Percentage is of column total. bPercentage is of sample total.
a
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Prevalence of Low Vision and Blindness in Upper Egypt 193
FIGURE 1. Major causes of blindness in Menia, Egypt.
TABLE 3. Adjusted odds ratios (logistic regression adjusting for all other factors) of risk factors for vision loss (visual acuity 56/18) in the total sample, Menia, Egypt. Characteristic
Category
Age Sex Marital status Occupation Education Household head Number of children per household Water source Method of sanitation Latrine Washroom Method of garbage disposal
Presence of animals Household construction material
Main source of income
n (%)
Female Widowed Farmer Unemployed Illiterate Age
321 109 392 87 269
(61.1) (20.7) (74.8) (16.5) (51.2)
Pump Well Tank inside No sanitation Evacuate 56 month Washroom no door Toilet not covered Burn Throw out Enclosure in house Mud Wood Stone Temporarily hired
91 8 325 81 22 25 112 79 122 224 139 13 59 241
(17.3) (1.6) (61.8) (15.5) (4.2) (4.8) (21.3) (15.1) (23.3) (42.7) (26.4) (2.4) (11.3) (45.9)
Adjusted OR
95% CI
1.1 2.5 14.4 1.7 1.8 3.8 1.03 1.1 4.9 3.8 3.8 7.4 1.02 2.9 2.2 3.4 12.4 7.7 5.03 2.04 1.9 4.8
(1.05–1.13) (1.57–4.26) (3.78–54.64) (1.25–5.34) (1.06–8.33) (1.9–7.5) (1.01–1.05) (1.09–1.34) (1.35–17.54) (1.58–9.05) (1.32–11.09) (1.81–30.26) (1.01–1.04) (1.17–7.18) (1.10–4.51) (1.19–9.51) (4.61–33.31) (2.31–12.17) (2.48–7.19) (1.64–7.28) (1.38–2.63) (1.26–18.14)
Reference group for each category: Sex, male; Marital status, divorced; Occupation, other; Education, postgraduate; Water source, general network; Sanitation, general network; Latrine, evacuate every 5 years; Washroom door, present; Toilet covered, yes; Garbage collection, collecting car; Animal enclosure in house, no; Household construction material,
DISCUSSION The prevalence of vision loss in Egypt has been reported since the early 1970s as relatively high.1,2,7–9 Similar to previous work in Egypt, we detected a high !
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prevalence of vision loss among the target population (unadjusted for clustering due to the small number of clusters) as well as low coverage of cataract and trichiasis surgical services, regardless of the high ratio of ophthalmologists to population in the governorate (&1:200,000). This high prevalence confirms previous
194 A. Mousa et al. TABLE 4. Adjusted odds ratios (logistic regression) of female-specific risk factors for vision loss (visual acuity56/18) in Menia, Egypt. Characteristic Marital status Occupation Education
Household head
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Number of children per household Children sleeping on the same pillow Water source
Sanitation method Washroom Method of garbage disposal
Existence of separate kitchen Presence of animals Household construction material
Source of income
Category
n (%)
Widowed Single Farmer Unemployed Illiterate Read and write Primary school Preparatory school Age Sex (female)
102 13 243 72 211 48 22 13
No separate pillow Pump Well General village tap Tank inside No sanitation Uncovered toilet Bathroom no taps Burn Fertilizer Throw out No Enclosure in house Animal dirt in house Mud Wood Stone No source of income
106 53 6 27 201 49 167 60 46 64 75 170 135 71 30 7 40 46
(31.9) (3.9) (75.7) (22.4) (65.7) (14.9) (6.9) (4)
117 (36.5) (32.9) (16.4) (2) (8.6) (62.5) (15.1) (54.9) (18.8) (14.5) (20.1) (23.4) (53) (42.1) (22) (9.2) (2.3) (12.5) (14.5)
Adjusted OR
95% CI
16.2 3.1 13.8 1.5 2.2 1.6 1.3 1.2 1.3 6.1 3.5 2.2 7.5 5.6 1.9 2.9 5.1 1.5 3.4 3.1 4.4 4.8 6.6 9.7 9.1 5.8 1.9 3.6 15.1
(2.51–52.73) (1.89–11.41) (7.21–18.65) (1.16–1.76) (1.03–3.69) (1.01–1.93) (1.21–1.68) (1.14–1.84) (1.18–5.01) (2.26–16.37) (1.82–6.42) (1.21–4.35) (1.27–14.56) (2.71–7.85) (1.23–5.32) (1.69–7.48) (2.18–9.49) (1.16–4.15) (1.87–21.11) (2.71–9.21) (2.28–13.57) (2.09–8.38) (1.61–9.42) (3.76–15.21) (4.48–14.74) (3.73–9.92) (1.16–5.31) (1.89–7.15) (2.82–29.24)
Reference group for each category: Marital status, divorced; Occupation, other; Education, postgraduate; Household head sex, male; Sleeping on separate pillow, yes; Water source, general network; Sanitation, general network; Toilet covered, yes; Bathroom tap, present; Garbage collection, collecting car; Separate kitchen, yes; Animal enclosure in house, no; Animal dirt, absent; Household construction material, others; Source of income, permanent job. CI, confidence interval; OR, odds ratio
findings in the literature and is similar to findings from Sudan (11%), however it is much higher than that of Libya (3.3%) and Saudi Arabia (2.6%).10,11 Additionally, our findings show that the major causes of visual impairment are more or less the same as in similar developing countries, i.e. cataract (53.7%) and uncorrected refractive errors (32.5%). Worldwide, women bear approximately two-thirds of the burden of severe visual impairment and blindness,13,14 the main reason being lower service use, especially in developing countries.11,14–16 In the current study we also detected a higher prevalence of vision loss in women compared to men (blindness 11.8% versus 5.4%; visual impairment 32.6% versus 26.8%, respectively). Regionally, Khandekar and co-authors, Al Gamra and co-authors, and Chiang and co-authors reported similar excess visual impairment and blindness among women compared to men in Oman, Qatar, and Palestine, respectively.17–19 Women had a slightly higher age-adjusted incidence of cataract compared to men, but this biological difference was small compared to the large difference in (age-adjusted) prevalence between men and
women.20 Globally, women account for 65% of cataract blindness because they are less likely to receive cataract surgery than men and they tend to seek surgery later. In some settings women have poorer surgical outcomes which can contribute to gender-specific barriers and attitudes towards service use.1,2 Women account for about two-thirds of the global burden of trachomatous trichiasis and the subsequent blindness due to corneal scarring. Although the prevalence of active disease is usually similar for boys and girls, adult women tend to have more active disease than adult men.21,22 This is probably due to their higher frequency of interaction with children.23 Recent reports show that trachoma is declining in many endemic countries. Prevention of trachoma and control of its ocular complications can be achieved through surgery to correct trichiasis, antibiotics to treat active disease, face washing and environmental improvements to reduce transmission.24–26 As yet, trachoma has not been mapped in Egypt and specific interventions are quite limited and it is likely that trachoma remains a public health problem in Menia and other selected governorates in Egypt. Ophthalmic Epidemiology
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Prevalence of Low Vision and Blindness in Upper Egypt 195 Recent epidemiologic studies have begun estimating female-specific risk factors for blindness.27 Our analysis found several female-specific risk factors for blindness that were not significant for the whole sample but were significant for women alone: being single, education ‘‘read and write,’’ ‘‘primary’’ and ‘‘preparatory’’ school levels, household head ‘‘female’’, ‘‘children sleeping on the same pillow’’, water source ‘‘general village tap’’, uncovered toilet, absence of washroom tap, using garbage as fertilizers, absence of kitchen, presence of cattle dirt, and having no source of income. Female-specific social determinants were associated with characteristics of the individual (education and source of income) as well as characteristics of the day-to-day activities that women undertake in rural areas (for example collecting water from the village tap, preparing fertilizers for cultivation, and so on). Having education and a permanent source of income generally empowers women in decision making within the household and community; conversely, women without education and a stable source of income have been shown to have less decision-making capacity related to use of eye care services compared to men.28 Poor hygienic and economic conditions are generally a reflection of reduced socioeconomic status which is well-recognized as a risk factor for blindness and use of eye care services.29 None of these factors are easily amenable to change. Egypt has sufficient clinical capacity to restore vision to most of those with vision loss (among whom almost two-thirds are women). According to an Egyptian Ophthalmologic Society report (2005), there are around 4000 Egyptian ophthalmologists, 40% of whom are registered as eye surgeons. Most ophthalmologists (including surgeons) congregate in urban areas; rural populations seldom use30 these services, even if these services are provided free of charge.31 Previous research has shown a high proportion of poor outcomes of cataract and trichiasis surgical services1,2 which would need to be addressed to improve uptake. The challenge, therefore, is linking populations in need with good-quality clinical services. The current study has a number of limitations including the relatively small sample size and the slightly higher number of un-examined men compared to un-examined women due to their availability during household examinations. It is possible that those who could not be examined due to their absence on examination days could have VA findings different to the examined population. Findings from a separate multivariate risk factor assessment model for men were not informative, being similar to those of the combined risk factor assessment. Previous research in the Nile Delta
!
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illustrated some of the sociocultural impediments that women face.32 Qualitative research is needed to better understand of how to address the barriers that women face to use of existing eye care services. In conclusion, the prevalence of low vision and blindness remains high in Egypt, particularly among women. Our data suggest that female-specific risk factors for vision loss relate to both sociodemographic as well as environmental factors, and that use of services is very low. A major national effort may be needed in order for Egypt to reach its VISION 2020 target.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper. The authors acknowledge the outstanding support from the Canadian Institute for Health Research (CIHR), The British Columbia Centre for Epidemiologic and International Ophthalmology, University of British Columbia as well as the technical support of Ms Priscilla Gikandi, Assistant Researcher, Research Unit, Department of Ophthalmology, King Saud University.
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