Ophthalmology Section DOI : 10.7860/JCDR/2020/42998.13441
Year : 2020 | Month : Jan | Volume : 14 | Issue : 01 Page : NC05 - NC09

Visual Impairment among Older Adults in Selangor State of Malaysia: The Grand Challenge Project

Mohd Harimi Abd Rahman1, Kee Qiu Ting2, Zainora Mohammed3, Norliza Mohamad Fadzil4, Suzana Sahar5, Mahadir Ahmad6

1 Senior Lecturer, Optometry and Visual Sciences Programme, Universiti Kebangsaan, Malaysia.
2 Senior Lecturer, Optometry and Visual Sciences Programme, Universiti Kebangsaan, Malaysia.
3 Senior Lecturer, Optometry and Visual Sciences Programme, Universiti Kebangsaan, Malaysia.
4 Senior Lecturer, Optometry and Visual Sciences Programme, Universiti Kebangsaan, Malaysia.
5 Professor, Centre of Healthy Aging and Wellness (HCARE), Universiti Kebangsaan, Malaysia.
6 Senior Lecturer, Health Psychology Programme, Universiti Kebangsaan, Malaysia.


NAME, ADDRESS, E-MAIL ID OF THE CORRESPONDING AUTHOR: Dr. Mohd Harimi Abd Rahman, Optometry and Vision Sciences Programme, Centre for Rehabilitation and Special Needs, Faculty of Health Sciences, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300, Kuala Lumpur, Wilayah Persekutuan, Malaysia.
E-mail: harimirahman@gmail.com
Abstract

Introduction

The increased prevalence of Visual Impairment (VI) in the elderly is in tandem with the increase of its populations in Malaysia.

Aim

This study was aimed to determine the prevalence and risk factors of VI among older adults in Selangor, Malaysia as it is one of the highly populated states in the country.

Materials and Methods

A total of 230 adults aged 60 years and above from the longitudinal study on neuroprotective model for healthy longevity (TUA) took part in this study from August 2018 to May 2019. Information on socio-demographic, smoking status and health condition were obtained through interview. Habitual distance Visual Acuity (VA) was measured using the Early Treatment Diabetic Retinopathy Study (ETDRS) chart. Refractive error was determined using retinoscopy technique followed by subjective refraction. Subjects’ height and weight were measured for their Body Mass Index (BMI). Descriptive statistics were used to determine the prevalence of VI and status of refractive error. Pearson correlation was used to determine correlation between household income and VI whereas Kendall’s Tau-b was used to determine correlation between age, educational level and smoking status with VI. Multivariate logistic regression was carried out to determine the risk factors of VI.

Results

Analysis was performed on 201 subjects (29 were excluded due to incomplete data) and the mean±SD VA for better eye was 0.23±0.20 logMAR. Overall, emmetropia has the highest percentage (37.3%), followed by hyperopia (34.3%) and myopia (28.4%). This study found that the prevalence of VI among older adults in Selangor was 27.3%. Pearson correlation showed significant correlation between monthly household income with VI. Kendall Tau-b showed a significant correlation between age, educational level and smoking status with VI. Multivariate logistic regression shows significant association between age older than 80-year-old with VI.

Conclusion

The prevalence of VI among the elderly in Selangor was notably high (27.3%) and greater age is associated with VI.

Introduction

The world’s elderly population is rising due to decline in fertility and increased longevity. Globally, there is approximately 9% elderly (aged ≥65) in 2019 and is expected to reach 12% in 2030 and 16% in 2050 [1]. The same phenomenon occurred in Malaysia as well. Population census showed an increment of Malaysian elderly from 6.3% in 2017 to 6.5% in 2018 and is expected to reach more than 7.0% in 2020 [2]. With aging of population, prevalence of VI is expected to increase as well [2]. Study in Malaysia also found that the increasing prevalence of VI with age was statistically significant [3,4]. It should be a concern as VI will affect the quality of life, physically, psychologically, environmental, and also social aspects [5-7].

Bourne RRA et al., reported the prevalence of VI worldwide differ according to the severity of VI [8]. Mild VI (VA 6/12 to 6/18 inclusive) was reported to be about 2.57%, moderate and severe VI (VA 6/18 to 3/60 inclusive) 2.95%, and blindness (VA less than 3/60) 0.49% among the world population of 7.33 billion [8]. Bourne RR et al., also found that 78% of the total number of VI was comprised of those aged 50 years and above [8]. Stevens GA et al., reported higher prevalence of VI in developing countries as compared to developed countries [9]. The prevalence of VI and blindness among population in USA aged 40 years and above was 2.14% and 0.68%, respectively [10]. Another developed country, Canada, showed a higher prevalence of VI, which was 5.7% among residents aged 45 to 85-year-old [11]. Study of VI among Singaporean population aged 40 to 80 years revealed a 26.87% low vision and a 1.09% blindness [12]. In Indonesia, it was 18.6% among residents aged 50 years and above [13]. National Eye Survey II (NES II) conducted in 2018 found 5.5% with moderate VI, 0.9% with severe VI and 1.2% blindness among Malaysian elderly population [14]. However, previous study at Sepang reported a 18.9% VI and a 2.9% blindness among residents aged 40 years and above [4].

Previous study on VI in Asia has found that VI could be influenced by demographic and socio-economic factors. Aging, low educational level and household income, systemic diseases including hypertension and diabetes as well as smoking were the common risk factors for VI [11,15-18]. However, there was limited information on risk factors of VI among Malaysian population especially in the elderly population. Moreover, previous study on VI only focused on specific regions in Selangor and unable to demonstrate its prevalence for the whole state of Selangor population [4,19,20]. Therefore, this study was carried out to determine the prevalence and risk factors of VI among older adults in Selangor by using correlation and regression analysis. This study also aimed to determine the status of VA and refractive error among older adults in Selangor.

Materials and Methods

This was a cross-sectional study involving Malaysian older adults who participated in the population-based longitudinal study on neuroprotective model for healthy longevity (Towards Useful Aging (TUA) Project) [21]. The TUA study recruited Malaysian older adults aged 60 and above. In this study, 12 places randomly selected from in the state of Selangor (Keramat, Klang, Tanjung Sepat, Kuala Langat, Tanjung Karang, Kuala Selangor, Petaling Jaya, Kelana Jaya, Sekinchan, Sungai Pelek, Batu 9 Cheras and Kajang). This study was conducted from August 2018 to May 2019. The sample size was determined based on Krejcie and Morgan’s sample size calculation [22];

s=X2 NP(1-P)÷d2 (N-1)+X2P(1-P)

Where s is the sample size, X is the table value of chi-square for 1 degree of freedom at the desired confidence level (1.96 for 95% confidence level), N is the population size (502200 older adults aged 60 and above in Selangor in 2018 [2], P is the expected prevalence (10.4% VI among residents aged 50 and above in central region of Malaysia (Selangor, Kuala Lumpur and Negeri Sembilan) [14] and d is the degree of accuracy expressed as proportion (0.05). The calculated sample size was added with 20% drop out. Hence, the sample size required was 172. In this study, we recruited 230 participants. However, complete data was only available from 201 subjects, and included in the analysis. The study adhered to the Declaration of Helsinki and was approved by the Medical Research and Ethics Committee of Universiti Kebangsaan Malaysia (UKM1.21.3/244/NN-2018-145). Signed informed consent was obtained from all subjects. The inclusion criteria were older adults aged 60 and above and without documented major psychiatric illnesses or mental disorders. Those participants with a Mini-Mental State Examination (MMSE) score of 14 and below indicating moderately severe or severe cognitive impairment were excluded [21].

Information on socio-demographic (age, races, gender, educational level, monthly household income), smoking status and health condition (hypertension and diabetic status) were obtained during history recording. Habitual distance VA was measured monocularly using the ETDRS chart at 3 m. The testing distance was reduced to 2 m or 1 m if participants failed to identify any letter at 3 m. Refractive error was determined using retinoscopy technique followed by subjective refraction. Subjects’ height and weight were measured using Leicester Height Measure (CMS Weighting Equipment, UK) and Tanita HD319 (Tanita Corporation of America, II, USA), respectively. Both height and weight were measured twice and average was used to calculate the BMI.

For analysis purposes, International Classification of Diseases 11th Revision (ICD-11) was used [23]. Based on ICD-11, habitual VA in better eye was used to classify subjects into no VI (VA≤0.30 logMAR), mild VI (0.30 logMAR<VA≤0.48 logMAR), moderate VI (0.48 logMAR<VA≤1.00 logMAR), severe VI (1.00 logMAR<VA≤1.30 logMAR) and blindness (1.30 logMAR<VA≤NLP) [23]. Refractive error was converted into Spherical Equivalent (SE) by adding spherical component to half of the cylindrical component. SE for eye with better distance habitual VA or right eye (if both eyes had equal VA) was used for the analysis. SE was classified into emmetropia (-0.50D≤SE≤+0.50D), myopia (SE<-0.50D) and hyperopia (SE>+0.50D) [24]. In this study, age was categorised into age group of 60 to 69-year-old, 70 to 79-year-old and over 80-year-old. The BMI was categorised into underweight (BMI<18.5 kg/m2), normal (18.5 kg/m2≤BMI≤22.9 kg/m2) and overweight (BMI≥23.0 kg/m2) [25].

Statistical Analysis

The statistical analyses were performed using SPSS statistics version 23.0. The normality tests showed that all the parameters were normally distributed (p>0.05). Descriptive statistics were used to determine the prevalence of VI and status of refractive error. Pearson correlation was used to determine correlation between household income and VI whereas Kendall’s Tau-b was used to determine correlation between age, educational level and smoking status with VI. Multivariate logistic regression was carried out on variable with p<0.20 in Pearson correlation and Kendall’s Tau-b to determine the risk factors of VI (p<0.05) [26].

Results

A total number of 230 subjects participated in this study. Only data of 201 subjects were analysed as 29 were excluded due to incomplete data. The subjects’ socio-demographic, smoking status, health condition and BMI were summarised in [Table/Fig-1].

Socio-demographic characteristics, smoking status, health condition and BMI of subjects.

CharacteristicsValue (n=201)
Races
Malay72 (35.8%)
Chinese100 (49.8%)
Indian29 (14.4%)
Gender
Male90 (44.8%)
Female111 (55.2%)
Mean age72.16±5.36 (Range: 64-89)
Educational level
No formal education23 (11.4%)
Primary63 (31.3%)
Secondary85 (42.3%)
Tertiary30 (14.9%)
Mean monthly household incomeRM2871.85±7451.12(Range: RM200-RM100,000)
Smoking status
Smoker15 (7.5%)
Former smoker20 (10.0%)
Non-smoker166 (82.5%)
Hypertension
Yes109 (54.2%)
No92 (45.8%)
Diabetes
Yes64 (31.8%)
No137 (68.2%)
BMI25.80±5.10 (Range: 14.84-58.60kg/m2)
Underweight8 (4.0%)
Normal52 (25.9%)
Overweight141 (70.1%)

Habitual distance VA for better eye ranged from -0.10 logMAR to 0.94 logMAR with mean of 0.23±0.20 logMAR. Refractive error of better eye ranged from -9.00D to +3.63D with mean of +0.08±1.66D. Overall percentage of refractive error shows highest percentage of emmetropia (37.3%), followed by hyperopia (34.3%) and myopia (28.4%). The prevalence of VI was 27.3%, in which 33 subjects (16.4%) with mild VI, 22 subjects (10.9%) with moderate VI and no subjects with severe VI or blindness.

Pearson correlation shows significant correlation between monthly household income with VI (r=-0.11, p=0.11). [Table/Fig-2] shows Kendall Tau-b between races, gender, age, educational level, smoking status, health condition and BMI with VI. Kendall Tau-b showed significant correlation between age, educational level and smoking status with VI. There was no significant correlation between races, gender, hypertension and diabetes status and BMI with VI.

Kendall Tau-b between races, gender, age, educational level, smoking status, health condition and BMI with VI.

123456789
1-
2-0.06
30.16*-0.18*
4-0.21*-0.21*-0.14*
50.070.28*0.040.00
60.02-0.040.15*-0.13*-0.02
70.10*-0.14*0.07-0.08-0.15*0.31*
8-0.09*0.07-0.06-0.07-0.040.17*-0.01
90.040.010.14*-0.23*0.18*-0.02-0.010.02-

1=Races 2=Gender 3=Age 4=Educational level 5=Smoking status 6=Hypertension 7=Diabetes 8=BMI 9=VI; *Significance, p<0.20


[Table/Fig-3] shows multivariate logistic regression between age, monthly household income, educational level and smoking status with VI. Multivariate logistic regression shows significant association between age >80 years with VI (OR=3.00, 95% CI=1.03-8.83). There was no significant association between monthly household income, educational level and smoking status with VI.

Multivariate logistic regression between age, monthly household income, educational level and smoking status with VI.

FactorsMultivariate logistic regression
Odd ratio (95% confidence interval)p-value
Age
60-69Reference
70-791.08 (0.51-2.28)0.85
80+3.00 (1.03-8.83)0.04*
Monthly household income1.00 (1.00-1.00)0.13
Educational level
No formal educationReference
Primary0.63 (0.23-1.73)0.37
Secondary0.38 (0.13-1.11)0.08
Tertiary0.36 (0.08-1.59)0.18
Smoking status
SmokerReference
Former smoker0.00 (0.00)1.00
Non-smoker2.16 (0.55-8.57)0.27

*Significance p<0.05


Discussion

Selangor is a state with highest population of older adults in Central region of Malaysia. It was estimated that there were 502200 older adults in Selangor state in 2018 as compared to 133400 and 177000 in Negeri Sembilan and Kuala Lumpur, respectively [2]. Moreover, there was increment of 5.8% of elderly population in Selangor towards 474800 older adults in 2017. Previous study had shown that aging drastically increases risk for VI, thus necessitates a study on it among older adults [15,17]. Hence, this cross-sectional study can provide data on prevalence and risk factors of VI in addition to determining status of VA and refractive error among older adults in Selangor.

This study found a higher prevalence of VI as compared to 7.6% prevalence of VI found in NES II [14]. This was due to present study defined VI as habitual distance VA worse than 6/12 whereas NES II only considered moderate VI (6/18<VA≤6/60), severe VI (6/60<VA≤3/60) and blindness (VA<3/60) in the determination of prevalence of VI. It is more appropriate to consider mild VI in determining the prevalence of VI as a VA worse than 6/12 may affect daily activities and it is the minimum requirement for driving in Malaysia [27]. Prevalence of VI in this study is higher as compared to 21.8% VI in Sepang district [4]. This can be attributed to the difference in classification of VI as previous study defined VI as VA worse than 6/18. Moreover, study in Sepang involved younger subjects (mean age 52.9 years) as compared to present study. Nowak MS and Smigielski J, found higher percentage of age-related eye diseases (cataract, age-related macular degeneration, glaucoma, ocular hypertension and diabetic retinopathy) among subjects in an older age group (≥60 years) as compared to subjects in a younger age group (35-59 years) [28]. The study reported older age was significantly associated with those age-related eye diseases. There was no blindness in present study as compared to 2.9% blindness found in Sepang [4]. The difference in findings was due to improvement in ophthalmology services provided by Ministry of Health Malaysia over the years [29]. As reported in National Eye Database 2007, there were increased cases of treated eye diseases among Malaysian. Our findings showed higher prevalence of mild and moderate VI and lower prevalence of severe VI and blindness as compared to 7.4% mild VI, 7.2% moderate VI, 1.2% severe VI and 2.8% blindness among residents of West Java aged 50 years and above [13]. This could be due to lag in healthcare services provided in Indonesia such as longer waiting time, inconsistent and inaccurate findings and lack of treatment options being offered, consequently led to the delayed in treating of the ocular diseases prior to onset of blindness [30]. In addition, Malaysia offered better healthcare services and attracted medical tourists from Indonesia, India, China and Australia.

This study showed highest percentage of emmetropia, followed by hyperopia and myopia. The higher prevalence of hyperopia was due to the gradually increase in lens thickness with aging but lens paradox caused a decrease in gradient-index of the lens and lead to hyperopic shift [31]. However, nuclear sclerosis of the lens caused myopic shift which explained the myopia population among elderly [32]. Similar findings were found in study by Hashemi H et al., which reported 42.3% emmetropia, 34.1% hyperopia and 23.6% myopia among the rural population aged 40 and above in Iran [33]. Previous study in Asian countries reported higher prevalence of hyperopia among the elderly (41.5%-55.7%) as compared to this study [32,34,35]. The difference in findings could be due to the studies’ were excluded because of their pseudophakic nature. Irving EL et al., found that the mean ocular refraction among elderly was significantly less hyperopic if those who undergone refractive surgery was not excluded [36]. The prevalence of myopia in our population is almost the same with elderly in Singapore (30.0%) and United Kingdom (27.8%) [35,37].

This study found that subjects over 80 years had increased risk for VI. Previous study in Asia also showed aging as a risk factor for VI [15,17,38,39]. This is due to increased risk of age-related ocular diseases such as cataract and macular degeneration with aging [40-42]. Study by Gan S et al., Tham YC et al., and Zimmerman EB et al., found low educational level was a risk factor for VI as high educational level had better awareness and understanding on information related to healthcare [38,39,43]. However, this study did not show an association between educational level and VI, it might be due to increasing geriatrics units and geriatricians practicing in healthcare services in Malaysia. Thus, every senior citizen is equally accessible to healthcare services regardless of their educational level [44].

This study showed gender was not significantly correlated with VI and this finding supported the studies by Nowak MS et al., Aljied R et al., and Thapa R et al., [11,28,45]. In contrast, Guo C et al., and Gan S et al., found that female had higher risk for VI due to less exposure to healthcare services [16,39]. Hence, it was not a surprise that present study did not find gender as a risk factor for VI as Malaysian population has equal exposure to healthcare services and treatments. This was proved by the National Eye Database 2017 report which showed that almost equal number of male and female patients who has undergone cataract treatment [46]. The present study found that races were not significantly correlated with VI. Similar results had been reported by Aljied R et al., and Wong TY et al., [11,47]. It could be attributed to the fact that there was no significant difference in utilization of healthcare services among Malaysian elderly of different races [48]. The present study did not found association between monthly household incomes with VI which contradicted with previous study [11,16]. The difference in findings can be attributed to the current study using monthly household income as compared to previous study using yearly household income. Smoking status was not associated with VI in this study as reported by Gan S et al., [39]. This finding was contradicted by a study in Canada which found that smoker was at higher risk for VI [11]. This might be due to, the study classify subjects who smoked at least once in the past month as smoker. It is also possible that non-smokers were passive smoker causing the true effect of smoking on VI cannot be shown. Report showed that about 37% people exposed to second hand smoke either at home or workplace [49]. There was no significant correlation between health condition (hypertension and diabetic status) with VI. The present study findings supported the study by Chong EW et al., and Tham YC et al., [15,38]. As reported by Tham YC et al., and Gan S et al., there was no significant correlation between BMI and VI shown [38,39]. However, Pongsachareonnont P et al., reported normal BMI had higher risk for VI as compared to obesity because obesity led to systemic diseases which increased the possibility for ocular examination as a routine medical check-up at healthcare center [50]. Whilst other study was only focusing on rural residents, this study comprised of the whole of Selangor population. It is worth to point out that the healthcare services in rural areas in Malaysia had been improved [51]. The strength of this study was the prevalence of VI among elderly and was based on habitual VA which was more relevant and reflective of the usual vision status of the subjects for daily activities.

Limitation(s)

There were few limitations in this study. Determination of VI was solely based on VA and visual field was not considered which may potentially underestimate prevalence of VI. Systemic diseases were self-reported which may not be accurate if the subject did not go for the annual medical check-up. Causes of VI were also not determined in this study.

Conclusion(s)

The prevalence of VI among the elderly in Selangor was higher (27.3%) as compared with the previous study in Malaysia. The percentage of emmetropia was the highest, followed by hyperopia and myopia. The risk factor for VI among the elderly in Selangor is aging. There was no significant association between gender, race, educational level, monthly household income, smoking status, systemic diseases and BMI with VI. Further study on causes of VI could be carried out for targeted ocular health intervention in the future.

1=Races 2=Gender 3=Age 4=Educational level 5=Smoking status 6=Hypertension 7=Diabetes 8=BMI 9=VI; *Significance, p<0.20*Significance p<0.05

References

[1]United Nations Department of Economic Social Affairs Population Division. World Population Prospects 2019: Highlights. New York; 2019  [Google Scholar]

[2]Department of Statistics Malaysia. Current Population Estimates. Jabatan Perangkaan Malaysia, Putrajaya; 2018  [Google Scholar]

[3]Zainal M, Ismail S, Ropilah A, Elias H, Arumugam G, Alias D, Prevalence of blindness and low vision in Malaysian population: Results from the National Eye Survey 1996 British Journal of Ophthalmology 2002 86(9):951-56.10.1136/bjo.86.9.95112185113  [Google Scholar]  [CrossRef]  [PubMed]

[4]Reddy S, Rampal L, Nurulaini O, Prevalence and causes of visual impairment and blindness in a rural population in Sepang district, Selangor Medical Journal of Malaysia 2004 59(2):212-17.  [Google Scholar]

[5]Amedo AO, Adade S, Koomson NY, Osae EA, Influence of visual impairment on the quality of life: a survey of patients reporting at the low vision centre of the eastern regional hospital of Ghana Journal of Ophthalmic Science 2016 1(3):0110.14302/issn.2470-0436.jos-16-940  [Google Scholar]  [CrossRef]

[6]Omar R, Rahman MHA, Knight VF, Mustaphal M, Mohammed Z, Mental health state and quality of life questionnaire in low vision assessment: A case report BMC Research Notes 2014 7(1):66710.1186/1756-0500-7-66725245590  [Google Scholar]  [CrossRef]  [PubMed]

[7]Omar R, Knight VF, Saat NZM, Kamarulzaman S, Alwi SNS, Visual impairment and quality of life among elderlies in nursing home Malaysian Journal of Health Sciences 2011 9(1):23-27.  [Google Scholar]

[8]Bourne RRA, Flaxman SR, Braithwaite T, Cicinelli MV, Das A, Jonas JB, Magnitude, temporal trends, and projections of the global prevalence of blindness and distance and near vision impairment: a systematic review and meta-analysis The Lancet Global Health 2017 5(9):e888-97.  [Google Scholar]

[9]Stevens GA, White RA, Flaxman SR, Price H, Jonas JB, Keeffe J, Global prevalence of vision impairment and blindness: Magnitude and temporal trends, 1990-2010 Ophthalmology 2013 120(12):2377-84.10.1016/j.ophtha.2013.05.02523850093  [Google Scholar]  [CrossRef]  [PubMed]

[10]Varma R, Vajaranant TS, Burkemper B, Wu S, Torres M, Hsu C, Visual impairment and blindness in adults in the United States: demographic and geographic variations from 2015 to 2050 JAMA Ophthalmology 2016 134(7):802-09.10.1001/jamaophthalmol.2016.128427197072  [Google Scholar]  [CrossRef]  [PubMed]

[11]Aljied R, Aubin M-J, Buhrmann R, Sabeti S, Freeman EE, Prevalence and determinants of visual impairment in Canada: Cross-sectional data from the Canadian Longitudinal Study on Aging Canadian Journal of Ophthalmology 2018 53(3):291-97.10.1016/j.jcjo.2018.01.02729784168  [Google Scholar]  [CrossRef]  [PubMed]

[12]Wah W, Earnest A, Sabanayagam C, Cheng CY, Ong MEH, Wong TY, Composite measures of individual and area-level socio-economic status are associated with visual impairment in Singapore PloS one 2015 10(11):e014230210.1371/journal.pone.014230226555141  [Google Scholar]  [CrossRef]  [PubMed]

[13]Syumarti RM, Ratnanina N, Halim A, Limburgh H, Prevalence and causes of blindness in people age 50 years and above, the intervention category and action required reducing blindness in West Java Province Indonesia J Ophthalmol Clin Res 2017 1(1):01-04.10.33140/JOCR/01/01/00005  [Google Scholar]  [CrossRef]

[14]Chew FL, Salowi MA, Mustari Z, Husni MA, Hussein E, Adnan TH, Estimates of visual impairment and its causes from the National Eye Survey in Malaysia (NESII) PloS one 2018 13(6):e019879910.1371/journal.pone.019879929944677  [Google Scholar]  [CrossRef]  [PubMed]

[15]Chong EW, Lamoureux EL, Jenkins MA, Aung T, Saw S-M, Wong TY, Sociodemographic, lifestyle, and medical risk factors for visual impairment in an urban asian population: The singapore malay eye study Archives of Ophthalmology 2009 127(12):1640-47.10.1001/archophthalmol.2009.29820008720  [Google Scholar]  [CrossRef]  [PubMed]

[16]Guo C, Wang Z, He P, Chen G, Zheng X, Prevalence, causes and social factors of visual impairment among Chinese adults: Based on a national survey International Journal of Environmental Research and Public Health 2017 14(9):103410.3390/ijerph1409103428885571  [Google Scholar]  [CrossRef]  [PubMed]

[17]Wang WL, Chen N, Sheu MM, Wang JH, Hsu WL, Hu YJ, The prevalence and risk factors of visual impairment among the elderly in Eastern Taiwan The Kaohsiung Journal of Medical Sciences 2016 32(9):475-81.10.1016/j.kjms.2016.07.00927638408  [Google Scholar]  [CrossRef]  [PubMed]

[18]Fraser-Bell S, Symes R, Vaze A, Hypertensive eye disease: A review Clinical & Experimental Ophthalmology 2017 45(1):45-53.10.1111/ceo.1290527990740  [Google Scholar]  [CrossRef]  [PubMed]

[19]Rozhan SMR, Halim I, Sha SA, Visual impairment and its associated factors among the adult population of Kuala Pajam village, Branang, Selangor, Malaysia Malaysian Journal of Community Health 2009 15(2):01-08.  [Google Scholar]

[20]Zainal M, Masran L, Ropilah AR, Blindness and visual impairment amongst rural Malays in Kuala Selangor, Selangor The Medical journal of Malaysia 1998 53(1):46-50.  [Google Scholar]

[21]Shahar S, Omar A, Vanoh D, Hamid TA, Mukari SZM-S, Din NC, Approaches in methodology for population-based longitudinal study on neuroprotective model for healthy longevity (TUA) among Malaysian Older Adults Aging Clinical and Experimental Research 2016 28(6):1089-1104.10.1007/s40520-015-0511-426670602  [Google Scholar]  [CrossRef]  [PubMed]

[22]Krejcie RV, Morgan DW, Determining sample size for research activities Educational and Psychological Measurement 1970 30(3):607-10.10.1177/001316447003000308  [Google Scholar]  [CrossRef]

[23]World Health Organization. International Statistical Classification of Diseases and Related Health Problems 10th Revision: Diseases of the eye and adnexa: Visual disturbance and blindness: World Health Organization; 2016 [cited 2017 May]. Available from: http://apps.who.int/classifications/icd10/browse/2016/en#/H54.9  [Google Scholar]

[24]Wong TY, Chong EW, Wong WL, Rosman M, Aung T, Loo JL, Prevalence and causes of low vision and blindness in an urban Malay population: The Singapore Malay Eye Study Archives of Ophthalmology 2008 126(8):1091-99.10.1001/archopht.126.8.109118695104  [Google Scholar]  [CrossRef]  [PubMed]

[25]Ismail IS, Bebakar W, Kamaruddin N, Abdullah N, Zin F, Taib S, Clinical practice guidelines on management of obesity 2004 PutrajayaMinistry of Health Malaysia, Academy of Medicine of Malaysia, Malaysian Association for the Study of Obesity, Malaysian Endocrine and Metabolic Society  [Google Scholar]

[26]Bendel RB, Afifi AA, Comparison of stopping rules in forward “stepwise” regression Journal of the American Statistical Association 1977 72(357):46-53.10.1080/01621459.1977.10479905  [Google Scholar]  [CrossRef]

[27]Haliza AM, Syah MMM, Norliza MF, Visual problems of new Malaysian drivers Malaysian family physician: The official journal of the Academy of Family Physicians of Malaysia 2010 5(2):95-98.  [Google Scholar]

[28]Nowak MS, Smigielski J, The prevalence and causes of visual impairment and blindness among older adults in the city of Lodz, Poland Medicine 2015 94(5):e50510.1097/MD.000000000000050525654398  [Google Scholar]  [CrossRef]  [PubMed]

[29]Pin GP, Hussein E, Mustari Z, Ismail M, The First Annual Report of the National Eye Database 2007 2008   [Google Scholar]

[30]Anon. Malaysia Poised to Become ASEAN Healthcare Hub. 2018 30th May 2019. Available from: https://healthcareasiamagazine.com/healthcare/in-focus/malaysia-poised-become-asean-healthcare-hub  [Google Scholar]

[31]Atchison DA, Markwell EL, Kasthurirangan S, Pope JM, Smith G, Swann PG, Age-related changes in optical and biometric characteristics of emmetropic eyes Journal of Vision 2008 8(4):29-29.10.1167/8.4.2918484868  [Google Scholar]  [CrossRef]  [PubMed]

[32]Kuang TM, Tsai SY, Liu CJL, Ko YC, Lee SM, Chou P, Changes in refractive status in an elderly Chinese population in a 7-year follow-up: The Shihpai Eye Study Journal of the Chinese Medical Association 2017 80(10):673-78.10.1016/j.jcma.2017.06.00428716601  [Google Scholar]  [CrossRef]  [PubMed]

[33]Hashemi H, Nabovati P, Yekta A, Shokrollahzadeh F, Khabazkhoob M, The prevalence of refractive errors among adult rural populations in Iran Clinical and Experimental Optometry 2018 101(1):84-89.10.1111/cxo.1256528702951  [Google Scholar]  [CrossRef]  [PubMed]

[34]Mohammed Z, Mansor SZ, Mohamed S, Refractive Error and Visual Acuity of elderly Chinese in Selangor and Johor, Malaysia Sains Malaysiana 2016 45(9):1393-98.  [Google Scholar]

[35]Tan CS, Chan YH, Wong TY, Gazzard G, Niti M, Ng TP, Prevalence and risk factors for refractive errors and ocular biometry parameters in an elderly Asian population: The Singapore Longitudinal Aging Study (SLAS) Eye 2011 25(10):1294-301.10.1038/eye.2011.14421720418  [Google Scholar]  [CrossRef]  [PubMed]

[36]Irving EL, Machan CM, Lam S, Hrynchak PK, Lillakas L, Refractive error magnitude and variability: Relation to age Journal of Optometry 2019 12(1):55-63.10.1016/j.optom.2018.02.00229567041  [Google Scholar]  [CrossRef]  [PubMed]

[37]Sherwin JC, Khawaja AP, Broadway D, Luben R, Hayat S, Dalzell N, Uncorrected refractive error in older British adults: The EPIC-Norfolk Eye Study British Journal of Ophthalmology 2012 96(7):991-96.10.1136/bjophthalmol-2011-30143022535330  [Google Scholar]  [CrossRef]  [PubMed]

[38]Tham YC, Lim SH, Shi Y, Chee ML, Zheng YF, Chua J, Trends of Visual Impairment and Blindness in the Singapore Chinese Population over a Decade Scientific Reports 2018 8(1):1222410.1038/s41598-018-30004-930111785  [Google Scholar]  [CrossRef]  [PubMed]

[39]Gan S, Zhou X, Yan J, Liu X, Yi J, Zhou X, The prevalence and risk factors of visual impairment among rural residents aged 50 years and above in Yugan county, China Ophthalmic Epidemiology 2018 25(5-6):331-37.10.1080/09286586.2018.147655729842804  [Google Scholar]  [CrossRef]  [PubMed]

[40]Alshamrani AZ, Cataracts pathophysiology and managements The Egyptian Journal of Hospital Medicine 2018 31(5560):01-04.10.12816/0042978  [Google Scholar]  [CrossRef]

[41]Panday M, George R, Asokan R, Ve Ramesh S, Velumuri L, Choudhari NS, Six-year incidence of visually significant age-related cataract: The Chennai eye disease incidence study Clinical & Experimental Ophthalmology 2016 44(2):114-20.10.1111/ceo.1263626290386  [Google Scholar]  [CrossRef]  [PubMed]

[42]Lim LS, Mitchell P, Seddon JM, Holz FG, Wong TY, Age-related macular degeneration The Lancet 2012 379(9827):1728-38.10.1016/S0140-6736(12)60282-7  [Google Scholar]  [CrossRef]

[43]Zimmerman EB, Woolf SH, Haley A, Understanding the relationship between education and health: a review of the evidence and an examination of community perspectives Population health: Behavioral and social science insights AHRQ Publication 2015 (15-0002):347-84.  [Google Scholar]

[44]Tan M, Kamaruzzaman S, Poi P, An analysis of geriatric medicine in Malaysia-riding the wave of political change Geriatrics 2018 3(4):8010.3390/geriatrics304008031011115  [Google Scholar]  [CrossRef]  [PubMed]

[45]Thapa R, Bajimaya S, Paudyal G, Khanal S, Tan S, Thapa SS, Prevalence and causes of low vision and blindness in an elderly population in Nepal: The Bhaktapur retina study BMC Ophthalmology 2018 18(1):4210.1186/s12886-018-0710-929439666  [Google Scholar]  [CrossRef]  [PubMed]

[46]Salowi MA, Mokhtar A, Omar NA, Hussin DA, Mokhtar NH, Adnan TH, The 11th Report of the National Eye Database 2017 Kuala Lumpur 2017   [Google Scholar]

[47]Wong TY, Tham YC, Sabanayagam C, Cheng CY, Patterns and Risk Factor Profiles of Visual Loss in a Multi-ethnic Asian Population: The Singapore Epidemiology of Eye Diseases Study American Journal of Ophthalmology 2019 206:48-73.10.1016/j.ajo.2019.05.00631095951  [Google Scholar]  [CrossRef]  [PubMed]

[48]Manaf NHA, Omar A, Omar MA, Salleh M, Determinants of healthcare utilisation among the elderly in Malaysia Institutions and Economies 2017 9(3):115-40.  [Google Scholar]

[49]Institute for Public Health. National Health and Morbidity Survey 2015-Report on Smoking Status Among Malaysian Adults. Institute for Public Health Kuala Lumpur, Malaysia; 2015  [Google Scholar]

[50]Pongsachareonnont P, Uramphorn N, Hounnaklang N, Association between visual status and mental health status in Thai rural elderly: A community-based study International Journal of Ophthalmology 2018 11(5):852-57.  [Google Scholar]

[51]Thomas S, Beh LS, Nordin RB, Health care delivery in Malaysia: Changes, challenges and champions Journal of Public Health in Africa 2011 2(2):e2310.4081/jphia.2011.e23  [Google Scholar]  [CrossRef]