Several studies have demonstrated that elderly persons have the highest rates of cataract, glaucoma, macular degeneration and diabetic retinopathy.1234 Normal visual changes that occur with ageing include presbyopia, decreased contrast sensitivity, decreased dark or light adaptation and delayed glare recovery.
Specific reports have shown that macular degeneration, open angle glaucoma, cataract and diabetic retinopathy were the most common causes of visual impairment in America.5 In a related study, the primary causes of visual loss in adults in the African-American and Hispanic populations in America were age related eye diseases, notably cataract and glaucoma, and age related macular degeneration in the white population.6 In a population based sample of U.S. Hispanic,7 visual impairment increased from 0.3% in those aged 40-49 years to 5.6% in those aged 60 yrs and above. The leading causes of low vision were cataract (42%), age related macular degeneration (15%) and diabetic retinopathy (13%). Open angle glaucoma was the leading cause of blindness among the same group. The main causes of visual impairment in Brazil8 were uncorrected refractive errors and senile cataract in people over 50 years old.
In Malaysia,9 uncorrected refractive errors (48.0%), and cataract (36%) were the major causes of visual impairment. In a population based eye survey conducted in south India,10 the prevalence of presenting visual acuity (VA) equal to or better 20/60 in both eyes was 59.4% and prevalence of presenting visual acuity of less than 20/200 in both eyes which is the definition of blindness in India was found in 11.0%.
In Bioko, Equatorial Guinea, the main causes of blindness were cataract (61.3%) macular degeneration (25.3%) optic atrophy (16%), glaucoma (13.3%) and ocular onchocerciasis (0.4%). Ocular onchocerciasis was very uncommon in such an area of high endemicity.11 The prevalence rates for blindness for in various studies done in Nigeria ranged between 0.78% in Benue Stat,12 0.95% in Anambra13 and Osun State14, and 2.7% in Kaduna State.15
Hence, as part of the community approach to health care for the elderly, this study sought to assess the prevalence of visual impairment and blindness among the older adults in Ife-Ijesha zone of Osun state, Nigeria. We aimed at determining the leading causes of visual changes in the older folks with a view to planning an eye care programme for the area.
Patients and Methods
Approval for the study was obtained from the Research and Ethics committee of the Obafemi Awolowo University Teaching Hospital Complex, Osun State, Nigeria. All participants gave informed consent.
A survey of ocular diseases in people aged 60years or older was conducted during an epidemiological study of health status of the elderly in Ife-Ijesha zone of Osun State of Nigeria between April and September 2002. The Ife-Ijesha zone of Osun State is situated on the rain forest belt of Nigeria. Three local government areas (LGA, s) in Ife-Ijesha zone of Osun state (Ife central, Ilesha West, and Obokun) were randomly selected for this study. Ile-Ife town (Semi-Urban centre) in Ife-Central LGA, Ilesha town (Urban) in Ilesha West LGA and Imesi-Ile (Rural centre) in Obokun LGA were used as the study centres.
We called for all residents aged 60 years and above through community leaders, announcements in religious houses, health centers and markets. They were invited for general health assessment including ocular assessment. This was the method allowed by the community leaders as strangers would not be allowed into individual homes in the community hence house to house survey was not possible.
A total of 681 elderly were seen. Of these 445 people aged 60 years and above who were found to have visual problems constituted the study group. They were screened for various eye ailments and blindness according to WHO definition. Information retrieved using structured questionnaires included patients′ demographic, social and clinical data such as sex, age, address, marital status, years of education, occupation, smoking, alcohol intake, sexual and marital history, history of ophthalmic problems and history of hypertension, hyperthyroidism, diabetes or cardiovascular diseases.
Participants were interviewed and underwent a comprehensive ophthalmic examination by an ophthalmologist. Examination carried out included VA measurement (using the Snellens chart, illiterate E-charts and Near-reading charts), intraocular pressure measurement (using Schiotz indentation tonometer by nurses) and Perkins applanation tonometer (by an ophthalmologist), fundoscopic examination (using direct and indirect ophthalmoscope by the ophthalmologist), and refraction (by an optometrist). VA assessment was done on all participants by three trained ophthalmic nurses who also recorded the history of the patient.
A diagnosis of cataract was defined as the presence of any opacity in the lens in any region in either eye as earlier described by Seah et al.17 We analyzed distinct types of cataract in a person as follows: nuclear only, cortical only, posterior subcapsular only or mixed. A diagnosis was based on presence of any of these opacities in either or both eyes.
Visual loss was classified according to WHO recommendations. Blindness means best corrected VA of < 10/200 or a visual field of < 10° from fixation. Best corrected VA of < 20/60 -10/200 or a visual field of 20°-10°from fixation was classified as low vision. Mono-ocular blindness was diagnosed where VA was < 20/60 in the worse eye with VA> 20/60 in the better eye. We could not determine patients′ visual fields because visual field analyzers were not available for this study. We did not take any retinal stereo photographs due to lack of facilities.
Glaucoma was diagnosed based on the presence of at least two of the following: Intraocular pressure above 25 mmHg (Indentation method) or 21 mmHg (Applanation) or more; vertical cup disc ratio 0.5 or more; asymmetry of 0.2 or greater in the absence of other ocular disease to explain the difference.18 However, in cases of multiple eye diseases in a participant, the major contributor was indicated as the cause of visual loss or blindness.
Those participants in whom VA impairment was attributable to geographic or hemorrhagic macular lesion following direct / indirect funduscopy in the absence of other causes of maculopathy were diagnosed as having age related macular degeneration.
The clinical findings were recorded in a form while the results were collated and analyzed using descriptive and analytical methods on SPSS statistical package on the computer. Those with ocular diseases were invited to attend follow up examination and management of their eye problems in the eye clinic of the Obafemi Awolowo University Teaching Hospital, Ile-Ife. On arrival at the hospital, these patients were given prompt attention and appropriate treatment was instituted.
Frequency distribution tables were used to present the data. Categorical variables were summarized as proportions and percentages while the Chi-square test and anova were used to compare the association between any two categorical variables. Mean and standard deviation were used for continuous variables. All test were two sided and at 5% level of statistical significance.
Four hundred and forty-five elderly whose ages ranged from 60 to 92 years constituted the study group. The mean age was 65.5 + 3.7 years. There were 148 males and 297 females; male to female ratio was 1: 2. A female preponderance was observed in all the age groups (Table 1). The difference in gender distribution was statistically significant (P < 0.0013).
Of the 445 people examined 25 people (5.6%) were binocularly blind while 19 (4.3%) were uniocularly blind. Two hundred and two people (45.4%) had low vision in both eyes while 71 people (15.9%) had uniocular low vision. Only 28.8% of the patients had normal vision, 21 patients (84%) with bilateral blindness were between 60 and 80 yrs most of those with binocular blindness were males 19 (76%) (Table 2), however, there were more females with uniocular blindness than males. This difference is however not statistically significant (P value = 0.015). Majority of the patients who had bilateral low vision were between 60 years and 80 years (Table 2). More females had uniocular low vision (P =0.825).
Cataract 12 (44.0%), glaucoma 10 (42.0%) and uncorrected aphakia 2 (8.0%) were the leading causes of bilateral blindness. The major causes of uniocular blindness were cataract 6 (31.5%) glaucoma 3 (15.5%) non-glaucomatous optic atrophy 3 (15.5%) and uncorrected aphakia 3 (15.5%). Uniocular low vision was caused mainly by cataract 43 (67.6%), glaucoma 12 (16.9%), pterygium 4 (5.6%), macular degeneration 3 (4.2%) and uncorrected aphakia 3 (4.2%) whilst bilateral low vision were caused mainly by cataract 101 (50.0%), and glaucoma 82 (40.6%). Corneal opacities were responsible for 2, (2.8%) uniocular and 3 (1.5%) bilateral low vision respectively.
When the total number of participants eye were considered cataract 30 (42.3%), glaucoma 23 (32.4%) and uncorrected aphakia 7 (9.9%) were the leading causes of blindness (Figure 1) and cataract 245 (54.2%) and glaucoma 176 (38.9%) were the most common causes of low vision followed by pterygium 10 (2.2%), corneal opacity 9 (1.8%) and refractive errors 6 (1.3%).
The subject of blindness in every age group and particularly the elderly have received a lot of attention in literature. While some cases are preventable others are not. Previous research in south western Nigeria has attributed 80%19 and 60%14 of blindness due to preventable causes.
It has been observed that the elderly frequently fail to utilize healthcare facilities. This is predicated upon a general poor health seeking behavior, fear of exorbitant fees, traditional healers / spiritual house patronage, and misappropriation of the possible significance of symptoms, which they attribute to ageing among other reasons. The optimum management of elderly patients also requires knowledge and skill related to rehabilitation and the best use of hospital and community based medical and social resources.
While the national estimated prevalence of blindness for Nigeria was put at 1%,20 there is no national figure on the prevalence of blindness among the elderly in Nigeria till date. We have recorded 5.6% and 4.3% for bilateral and uniocular blindness respectively for this group of Nigerians. A national survey is obviously overdue and should be given due attention. A clinic based study in Anambra state reported 14% and 27.6% bilateral and uniocular blindness respectively.16 The difference between the present study and Anambra report can largely be attributed to the study type i.e clinic based versus community based. Other possible reasons for the differences include population type, environmental differences and cultural practices.
An age related analysis when compared with international figures, the same prevalence rate of bilateral blindness (5.6%) was recorded in people aged 65 or older in a population based sample of U.S. Hispanics.7 The prevalence of bilateral blindness among nursing home residents in Baltimore was found to be 17.0%. However the study showed that the frequency of blindness increased from 15.2 percent among those under 60 years to 28.6 percent among those 90 years or older.21 This was usually in association with numerous other health problems of which eye problems are not uncommon. While these figures appear escalated, they could be a result of the study among a concentrated specific population of the elderly.
The prevalence rate of visual impairment was found to be 2.7% in a Taiwanese population aged 50years and above,22 while blindness was only 2.2%. This may be due to difference in sample size.
Like other studies have shown,1621 cataract was the leading cause of blindness in the study population. Glaucoma (again, similar to others) ranked next. This is however in variance with the U.S Hispanic study7 where myopic macular degeneration was reported as the second leading cause of blindness.
According to Nwosu,16 the leading causes of bilateral blindness in Anambra State were cataract, (33.3%), glaucoma (22.2%) and macular degeneration (11%); visual impairment was caused mainly by cataract (33.2%), uncorrected refractive error (19.5%), and glaucoma (15.5%). Uncorrected refractive errors were found in 12% of our study population, majority (66.7%) was due to couching. This study affirmed that couching is still widely practiced as a method of cataract extraction in the study area.
Prevalence of blindness in an Indian population with best corrected VA was 4.6% and they recorded a significant reduction in the burden of blindness after proper correction of refractive errors.10 Majority of patients (56.7%) in our study did not turn up for refraction till the time of this report and so we could not say to what extent correction of refractive errors would reduce the burden of blindness among the study population. Default from follow up care is a major problem among Nigerians.13
Cataract was the principal cause of blindness in at least one eye in 70.6% of blind people. Cataract caused more uniocular low vision (67%) than uniocular blindness (31.5%) in our study and also more females have uniocular low vision than their male counterparts. It could be inferred that women have higher age adjusted prevalence of severe cataract compared with men. The gender difference was not statistically significant, (p =0.9618).
Non-glaucomatous optic atrophy was found in 15.5% of uniocular blind people. This was due to optic neuritis, trauma and nutritional deficiency.
The prevalence of blindness and visual impairment in this study population is high. This finding in a community where most of the elderly are fast losing traditionally accorded attention due to civilization and urban movement call for a great concern. The two main causes of blindness and visual impairment in our study were either treatable or preventable causes and so intensification of effort on control programmes in this area is desirable. A comprehensive eye care programme is suggested, so as to reduce this burden of blindness and visual impairment.
We recommend that prevention and control of avoidable blindness needs to be an on going focus in Nigeria, especially in Ife-Ijesha zone of the country. Additional educational programmes should be developed to improve individual awareness of age related ocular diseases and availability of current ophthalmic intervention.
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