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Gloria C. E, Nneli R. O, Anyaehie U. B, Chiamaka O, Osims E. E. Prevalence, Determinants and Distribution of Refractive Errors in a Nigerian Community. Biosci Biotech Res Asia 2011;8(2)
Manuscript received on : July 03, 2011
Manuscript accepted on : August 15, 2011
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Prevalence, Determinants and Distribution of Refractive Errors in a Nigerian Community

C. Emerole Gloria1,2, R. O. Nneli2, U. B. Anyaehie3, Okereke Chiamaka3 and E.E . Osims4

¹Optometry Clinic, Federal Medical Centre, Owerri Nigeria.

²Department of Physiology, College of Medicine, Abia State University, Uturu Nigeria.

³Department of Physiology, College of Medicine, University of Nigeria, Enugu Campus Nigeria.

4Department of Physiology, College of Medical Science and Health Science, Abia State University, Uturu Nigeria.

Corresponding Author E-mail: ugobond@yahoo.com  

ABSTRACT: Refractive errors have been identified as major cause of blindness yet there is little known about the prevalence, distribution and determinants in Nigeria. We present the results od a cross sectional analytical study using 3451 adults living in Owerri, Nigeria. Results show a high prevalence of refractive errors (79.5% and 76.6% in the study and control respectively). Hyperopia was the dominant refractive error; while Myopia (23.4% and 19.6%) and Astigmatism (20.9% and 22.5%) was noted among subjects in study and control groups respectively. A higher prevalence exists among rural dwellers and the contributory factors were environmental factors, poor nutrition and use of irrational and uncontrolled use of chloroquines as first line drugs for malaria. To achieve the targets of the Global Initiative for Elimination of avoidable blindness, we recommend Health education on diet, drug use and safe environmental practices especially for people living in rural areas in developing countries.

KEYWORDS: Refractive errors; Eye; Blindness; Nigeria; Imo State

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Gloria C. E, Nneli R. O, Anyaehie U. B, Chiamaka O, Osims E. E. Prevalence, Determinants and Distribution of Refractive Errors in a Nigerian Community. Biosci Biotech Res Asia 2011;8(2)

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Gloria C. E, Nneli R. O, Anyaehie U. B, Chiamaka O, Osims E. E. Prevalence, Determinants and Distribution of Refractive Errors in a Nigerian Community. Biosci Biotech Res Asia 2011;8(2). Available from: https://www.biotech-asia.org/?p=9408/

Introduction

The human eye is an important special sensory organ whose primary function, vision is achieved by refraction of light rays by the cornea and the crystalline lens and focusing them on the retina. The retina receives the pictures formed by the light rays and send image to the brain via the optic nerve for perception1, 2.

An individual’s ocular refractive status is a physiology parameter hence affected by age, nutrition, diseases, and changes in the internal /external environment of the individual.

Refractive errors of which there are three types- astigmatism, hyperopia and myopia. are not diseases but are eye disorder that can impair vision if not corrected 3.

Worldwide estimates of the number of people with refractive errors range from 800 million to 2.3 billion. Numerous studies have been undertaken on small samples from disparate populations and extrapolations from these data have provided clues about refractive error distribution in many developed countries4, 5. There is little known about the prevalence of refractive errors in the adult population of Nigeria6

The detection and correction of refractive errors is a cost effective intervention and is one of the priorities under the disease control component of the Global Initiative for Elimination of Avoidable blindness.7 Uncorrected refractive error is a significant cause of blindness and a leading cause of visual impairment in developed countries 7. It is clear that without appropriate optical correction, millions of children lose educational opportunity and many adults are excluded from productive working lives with severe economic and social consequences7.

The present study was aimed at determining the prevalence and determinants of refractive errors in Owerri, Imo State in order to create a data baseline for the state.

Materials

Subjects (2606) were recruited between September 2007 and November 2009 from persons who attended the Federal Medical Centre Owerri. The controls (845) were selected from persons living in a near by rural community in Owerri-West Local government Area, after a Multistage random sampling. Only those above 18 years were selected for the study.

Structured interview administered questionnaires were used to determine demographic characteristics, dietary habits, alcohol consumption, tobacco use and past ocular history was administered to subjects and then detailed history of ophthalmic and systemic problems was obtained.

Those with conditions interfering with accurate ocular refractions such as corneal opacity, visually impairing opaque media, diabetes mellitus and hypertension and those are pseudophakic or aphakic were excluded from analysis.

Methods

All the subjects underwent a complete ophthalmic examination which included measurement of distant, near and pin hole visual acuity in subjects with visual acuity less than 6/6(with Snellen’s chart and near reading charts); tonometry; fundoscopy; and perimetry to investigate other possible causes of impairment or reduction in vision.  Results analysis was done using EPI Info version 3.5, 2008 statistical Data Package.

Results

 Demographic characteristics of subjects

Majority of the subjects were aged 40-49. There were more females than males in both in both study and control groups. There was no significant difference between the control and the study groups as shown in table 1.

Table 1: Subjects by age and  gender.

AGE                  MALE             FEMALE  
  STUDY

N=1079

CONTROL

N=357

STUDY

 N=1527

CONTROL

N=488

P VALUE
  No % No % NO % NO %  
20 -29 194 18.0 32 9.0 340 22.3 89 18.2 0.5
30-39 183 17.0 50 14.0 260 17.0 122 25.0 1.00
40-49 279 25.8 170 47.6 441 28.9 189 38.7 0.12
50-59 244 22.6 65 18.2 296 19.4 47 9.6 0.49
60-69 179 16.6 40 11.2 190 12.4 41 8.4 0.32

X2 =2.42,df=1, p-value=0.12,or=0.9,95% C.I=0.70-1.06[UNIVARIATE]

X2=1.36, df=4,p-value=0.850[ BIVARIATE]

Refractive Status of Patients

Majority of the subjects (79.5% and 76.6% of the study and control groups respectively) had ametropia. Only 20.5 % and 23.2% of the study and control respectively were emmetropic. The differences between the study and control groups were not statistically significant. The commonest refractive error was hyperopia(35.2% and 34.7% of the study and control groups respectively) followed by myopia(23.4% and19.6% of the study and control groups respectively). The least was astigmatism (20.9% and 22.5% of the study and control groups respectively). These findings are shown in table 2

Table 2: Refractive Status of Patients.

Refractive Status          Study group

          N=2606

      Control group

           n=845

P value
No % No %
Hyperopia 917 35.2 293 34.7 1.00
Myopia 610 23.4 166 19.6 0.60
Astigmatism 545 20.9 190 22.5 0.73
Emmetropia 534 20.5 196 23.2 0.73

X2=0.27,df= 1,p-value=0.60,OR=1.19,95% C.I=0.58-2.48[UNIVARIATE]

X2 = 0.7,df=3,p=0.873[BIVARIATE]

Ammetropia and Risk Factors Affecting Vision

About sixty seven percent and forty nine percent of ametropics in the study and control groups respectively used chloroquine as their regular anti-malarial while  62.2 % in the study group and 31% in the control group were in the habit of consuming food items of low nutritional values as shown in table 5.

Table 3: Prevalence Of Ametropia In Different Age Groups And Gender:

Age

(years)

                         Male                        Female P value
Study group

N=827

Control group

N=266

Study group

N=1245

Control group N=383  
No % No % No % no %  
20-29 148 18.0 24 9.0 285 22.9 72 18.8 0.38
30-39 141 17.0 38 14.3 209 16.8 93 24.3 1.00
40-49 217 26.2 127 47.7 370 29.7 153 39.9 0.53
50-59 188 22.7 50 18.8 231 18.6 34 8.9 0.49
60-69 133 16.1 27 10.2 150 12.0 31 8.1 0.41

X 2 =0.77,df=1, p-value =0.38, 95% confidence interval =0.35-1.55[univariate]

X2 = 1.55, df = 4, p-value =0.818[Bivariate]

Table 4: Ametropia and Location Of Residence Of Subjects

Gender           Urban residence         Rural residence p-value
Study group

N=804

Control group

N=251

Study Group

N=1268

Control Group

n=398

No % No % No % No %
Male 445 55.3 134 53.5 530 41.8 158 39.8 0.06
Female 359 44.7 117 46.5 738 58.2 240 60.2 3.38

X2 =3.38,df=1, p-value=0.06, OR= 1.7, 95% C.I =0.93-3.07[univariate]

X2 =3.96,df=1,p-value=0.046[Bivariate]

 

Table 5: Ammetropia and Risk Factors Affecting Vision.

Risk factors      Study group

        N=2072

     Control group

       N=649

p-value
No % No %
Alcohol consumption 696 33.6 178 27.4 0.280
Tobacco use 412 19.9 98 15.1 0.350
Quinines as most used anti-malaria 1405 67.6 319 49.2 0.010
History of ocular Trauma 421 20.3 193 29.7 1.00
Poor dietary Habits 1288 62.2 205 31.6 0.001

X2= 20.4 ,df=1, p-value= 0.001, OR=3.8,95%C.I=2.02-7.27[Univariate]

Discussion

In this study, the majority of the subjects were aged 40-49 years (27.6%  and 42.5% of the study and control groups respectively). The decline in vision at near from presbyopia and hyperopia as the lens becomes rigid may explain why majority of those who presented for visual care were in this age group. After the age of 40 years lens cannot change its shape as it once easily did due to increasing rigidity  therefore it becomes more difficult to see clearly at closed range1,3. Most domestic and office duties are at near point activities and demand good near vision. Ageing also modifies a pre-existing error making it more symptomatic 6.

There were more women in this study (58.6% and 57.8% of the study and control groups respectively). Women as a result of pregnancy, child birth and motherhood are more health conscious than men. This agrees with earlier studies6,8,9.

The prevalence of ametropia in this study was 79.5% and 78.6% in the study and control groups respectively. Studies done in the United States of America, Western Europe and Australia showed a prevalence of 35.1%,37.7% and 22.2%. 10 respectively. The relatively high prevalence rate of refractive errors in this study appears paradoxical as demographic studies have shown that Asia and America harbour more aged population than developing countries like Nigeria since increase in age is a physiologic determinant of refractive errors11. This observation shows that the environment may be a factor in this high prevalence.

Ametropia was found more in females and rural dwellers. The influence of the environment on ocular physiology has been earlier noted12-16. In the rural settings, women may be more exposed to hazard due to pollution of the environment from use of firewood for cooking, bush burning practices, cow’s skin and hides, long exposure to ultraviolet rays from sunlight during farming, use of lantern/candle to read and dusty environment especially during harmattan and dry season.

The most dominant refractive error was hyperopia (35% and 34.7% in the study group and control group with no significant difference between the two groups, p=1.00) while myopia was found in 23.4% and 19.6% of the study and control groups respectively. This is similar to the findings in earlier study done in the western Nigeria among public drivers  17 . The studies done in United States of America, Western Europe and Australia however showed a prevalence of 9.9%, 11.6% and 5.8% hyperopia10. Factors responsible for ametropia in our environment probably cause a decline in the accommodation of the lens causing more of  hyperopia than myopia.  A prevalence of 20.9% and 22.5% of astigmatism was found in the study and control groups respectively. Hyperopic and myopic astigmatism was also found in some subjects. This was similar to the prevalence of 27.4% of astigmatism found in the pilot study among patients attending the eye clinic of the University Of Nigeria  Teaching Hospital6. The studies done in Sumatra Indonesia and India (APEDS showed a  prevalence of 18.5% and 12.9% astigmatism11. This may be due to differences in genetic and environmental factors.

Among factors that are very likely to affect refractive ability of the eyes are the use of choroquine as anti-malarial drugs and poor dietary habits. About sixty seven percent and forty nine percent of ametropics in the study and control groups respectively used chloroquine as their regular anti-malarial. Malaria is endemic in Nigeria and the choroquine is used as first line drug especially in the rural areas. Abuse of choloroquine affects components of refraction especially in the absence of adequate nutrition1.Many of the ametropics (62 % in the study group and 31% in the control group) were in the habit of consuming food items of low nutritional values. The effect of nutritional deficiencies on visual health has been noted1. From this study, poor dietary habit may be implicated as a risk factor for ametropia.

It is not evident from our study that ocular trauma, the use of alcohol and tobacco significantly affect the prevalence of ametropia.

Conclusion

This study has provided information on the prevalence of refractive errors among adults in Imo state, Nigeria. The level of prevalence was high compared with the levels in high and medium income resource countries. The marked difference may be due to the identified poor level of nutrition and frequent use of chloroquine derivatives for the treatment of malaria and living in the rural area.

Recommendation

Regular screening exercise for ametropia is recommended in to identify those with refractive errors for early corrective measures. Health education on diet, drug use and safe environmental practices should be incorporated as one of  the priorities under the disease control component of the Global Initiative for Elimination of avoidable blindness

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