Selvaraj Sivasubramaniam

Causes of blindness and visual impairment in Nigeria: the Nigeria national blindness and visual impairment survey.

PURPOSE Determine causes of blindness and visual impairment among adults aged >or=40 years. METHODS Multistage, stratified, cluster random sampling with probability proportional to size procedures were used to identify a nationally representative sample of 15,027 persons >or=40 years of age. Distance vision was measured with a reduced logMAR tumbling E-chart. Clinical examination included a basic eye examination of all subjects and a more detailed examination of those who had presenting vision <6/12 in either eye. Cause for vision loss was assigned to all subjects with presenting vision <6/12 in any eye. RESULTS Of the 15,122 persons aged >or=40 years who were enumerated, 13,599 (89.9%) were examined. In 84%, blindness was avoidable. Uncorrected refractive errors were responsible for 57.1% of moderate (<6/18-6/60) visual impairment. Cataract (43%) was the commonest cause of blindness (<3/60). Prevalence of cataract-related blindness was 1.8% (95% CI: 1.57-2.05) and glaucoma-related blindness was 0.7% (95% CI: 0.55-0.88). Increasing age was associated with increasing prevalence of all major blinding conditions. Females, illiterate persons, and residents in the North East geopolitical zone had significantly higher odds of cataract-induced blindness and severe visual impairment. CONCLUSIONS The high proportion of avoidable blindness, with half being attributable to cataract alone and uncorrected refractive errors being responsible for 57% of moderate visual impairment, means that appropriate and accessible refraction and surgical services need to be provided. If priority attention is not given, the number of blind and severely visually impaired adults in Nigeria will increase by >40% over the next decade.

Couching in Nigeria: prevalence, risk factors and visual acuity outcomes.

Purpose: Couching is an ancient treatment for cataract which is still practiced in some of the poorer developing countries, particularly in sub-Saharan Africa. The purpose of this study is to describe risk factors for couching and visual acuity outcomes in a nationally representative sample of adults aged 40 years and above in Nigeria. Methods: Probability in proportion size methods were used to identify a representative sample. Of the 15,375 adults enumerated, 13,582 were interviewed and examined. Examination included logMar acuities, slit lamp examination and dilated fundoscopy with digital fundus imaging. Results: Almost half of the 583 eyes undergoing a procedure for cataract had been couched (249 eyes, 42.7%). Individuals living in rural areas (P = 0.033) and in the two underserved northern administrative zones (P = 0.33; P = 0.002) were more likely to have been couched. Visual outcomes were poor according to World Health Organization categories, with 55.8% of people and 73.1% of eyes having a presenting visual acuity of less than 3/60 and only 9.7% and 2.4% of people and eyes respectively having a good outcome (6/18 or better). None were wearing an aphakic correction, and with correction acuities improved but 42.6% of eyes were still blind (< 3/60). Conclusions: Couching is still widely practiced in Nigeria and visual outcomes are very poor. The population needs to be made aware of the risks associated with the procedure, and services for high quality, affordable cataract surgery need to be expanded, particularly in rural areas and in the north of the country.

Refractive Error in Nigerian Adults: Prevalence, Type, and Spectacle Coverage

PURPOSE To provide data on prevalence and types of refractive error and the spectacle-wearing rate among adults in Nigeria and the degree to which the need for distance correction could be met by off-the-shelf spectacles. METHODS Multistage, stratified, cluster random sampling with probability proportional to size was used to identify a nationally representative sample of 15,027 persons aged ≥40 years. Distance vision was measured using a reduced logMAR tumbling-E chart. All participants underwent autorefraction, and those with presenting acuity of <6/12 in one or both eyes had their corrected acuity measured and underwent detailed clinical examination to determine the cause. RESULTS Included in the survey were 13,599 (89.9%) of the 15,122 persons aged ≥40 years who were enumerated. Uncorrected refractive error was responsible for 77.9% of mild visual impairment (<6/12-6/18), 57.1% of moderate visual impairment (<6/18-6/60), 11.3% of severe visual impairment (<6/60-3/60), and 1.4% of blindness (<3/60). The crude prevalence of myopia (≤0.5 D) and high myopia (≤5.0 D) were 16.2% and 2.1%, respectively. Spectacles could improve the vision of 1279 (9.4%) and 882 (6.5%) participants at the 6/12 and 6/18 level, respectively, but only 3.4% and 4.4% of these individuals wore spectacles to the examination site. Approximately 2,140,000 adults in Nigeria would benefit from spectacles that improved their vision from <6/12 to ≥6/12. More than a third of the need could be met by low-cost, off-the-shelf spectacles. CONCLUSIONS Uncorrected refractive errors are an important cause of visual impairment in Nigeria, and services must be dramatically improved to meet the need.

Coverage of Hospital-based Cataract Surgery and Barriers to the Uptake of Surgery among Cataract Blind Persons in Nigeria: The Nigeria National Blindness and Visual Impairment Survey

Purpose: To determine cataract surgical coverage, and barriers to modern cataract surgery in Nigeria. Methods: Multistage stratified cluster random sampling was used to identify a nationally representative sample of 15,027 persons aged 40+ years. All underwent visual acuity testing, frequency doubling technology visual field testing, autorefraction, and measurement of best corrected vision if <6/12 in one or both eyes. An ophthalmologist examined the anterior segment and fundus through an undilated pupil for all participants. Participants were examined by a second ophthalmologist using a slit lamp and dilated fundus examination using a 90 diopter condensing lens if vision was <6/12 in one or both eyes, there were optic disc changes suggestive of glaucoma, and 1 in 7 participants regardless of findings. All those who had undergone cataract surgery were asked where and when this had taken place. Individuals who were severely visually impaired or blind from unoperated cataract were asked to explain why they had not undergone surgery. Results: A total of 13,591 participants were examined (response rate 89.9%). Prevalence of cataract surgery was 1.6% (95% confidence interval 1.4–1.8), significantly higher among those aged ≥70 years. Cataract surgical coverage (persons) in Nigeria was 38.3%. Coverage was 1.7 times higher among males than females. Coverage was only 9.1% among women in the South-South geopolitical zone. Over one third of those who were cataract blind said they could not afford surgery (36%). Conclusions: Cataract surgical coverage in Nigeria was among the lowest in the world. Urgent initiatives are necessary to improve surgical output and access to surgery.

Review of the publications of the Nigeria national blindness survey: Methodology, prevalence, causes of blindness and visual impairment and outcome of cataract surgery

This is a review of the major publications from the Nigeria national blindness survey in order to highlight major findings and challenges of eye care in Nigeria. The review summarizes methodology and key findings. Survey publications on methodology, prevalence and causes of visual impairment and outcome of cataract surgery were retrieved, reviewed and relevant data extracted, reported and discussed. The study was the largest and more detailed eye survey in Nigeria (15,375 people 40 years and older recruited). Participants had detailed eye examination including visual acuity, autorefractokeratometry, A- scan biometry, visual field and basic eye examination. Cause(s) of visual impairment in each eye using WHO algorithm was determined among participants with vision < 6/12. Some of the participants also had qualitative questions on barriers to uptake of services, quality of life and visual function. Major highlights of the results as contained in the publications include a high prevalence of blindness with 4.2% (95% CI: 3.8-4.6%;),of the study population having blindness (using presenting vision (PVA)) even with best correction the prevalence was 3.4% (95% CI: 3.0-3.8%. The prevalence of SVI using PVA was 1.5% (95% CI: 1.3-1.7%).and with best correction 0.8% (95% CI: 0.7-1.0%). Blindness varied by age groups, sex, literacy level and geopolitical zone. Furthermore, 84% of blindness was due to avoidable causes with cataract responsible for 43% of blindness, glaucoma 16.7%, uncorrected aphakia 8.4% and corneal opacity 7.9%. Of the total 538 eyes that had cataract surgery procedures, 42.7% had couching and the remaining had cataract surgery, but only 41.4% of cataract operated eyes had IOL surgery. Outcome of cataract surgery was good at presentation for only 30.8% of eyes (84 eyes) which improved to 56.8% with correction. The possible remedy for the high burden of needless blindness and harmful eye health practices in Nigeria are discussed.

Prevalence, causes, and risk factors for functional low vision in Nigeria: results from the national survey of blindness and visual impairment.

PURPOSE To estimate prevalence and describe causes of functional low vision (FLV) among a nationally representative sample of Nigerian adults, assess socioeconomic risk factors, and estimate the number of adults in Nigeria who might benefit from low vision assessment or rehabilitation services. METHODS Multistage, stratified, cluster random sampling with probability proportional to size procedures were used to identify a nationally representative sample of 15,027 persons aged 40 years or older. Distance vision was measured using a reduced logMAR tumbling E-chart. All participants with presenting acuity of <6/12 in one or both eyes had their corrected acuity measured and underwent detailed clinical examination to determine the cause. FLV was defined as best corrected vision <6/18 in the better eye, after excluding those with no light perception in both eyes and those with treatable causes. Analysis took account of the clustered design. RESULTS In all, 13,591 individuals were examined in 305 clusters (response rate, 89.9%). The crude prevalence of FLV was 3.5% (95% confidence interval, 3.1-3.9%). This was lower than the prevalence of blindness, which was 4.2%. Glaucoma was the most common cause and age the most important risk factor. There are estimated to be approximately 5000 adults with FLV per million population and 340 who are totally blind. Only 9.3% of those with FLV were of working age and literate. CONCLUSIONS These are the first data on the prevalence, causes, and risk factors for FLV from Africa. Results support studies from Asia that the prevalence of FLV is lower than previously thought. Because the majority of adults with FLV in Nigeria live in rural areas and are elderly and not literate, further research is required to assess the nature of the interventions required and who might best deliver them.

Ecological determinants of blindness in Nigeria: the Nigeria National Blindness and Visual Impairment Survey.

OBJECTIVE To determine the prevalence and causes of visual loss in different ecological zones across Nigeria. METHODS A population-based survey using multi-stage, stratified, cluster random sampling with probability proportional to size comprising a nationally representative sample of adults aged > or = 40 years from six ecological zones. OUTCOME MEASURES Distance vision was measured using reduced logMAR charts. Clinical examination included basic eye examination for all respondents and a detailed examination including visual fields, gonioscopy and fundus photography for those who were visually impaired or blind (i.e. presenting vision < 20/40 in the better eye). A principal cause of visual loss was assigned to all respondents with presenting vision < 20/40 in the better eye. RESULTS A total of 15 122 persons aged > or = 40 years were enumerated, 13 599 (89.9%) of whom were examined. The prevalence of blindness varied according to ecological zone, being highest in the Sahel region (6.6%; 95% confidence interval (CI) 4.2 - 10.4) and lowest in the rain forest region (3.23%; 95% CI 2.6 - 3.9). Age/ gender-adjusted analyses showed that risk of blindness was highest in Sahel (odds ratio (OR) 3.4; 95% CI 2.1 - 5.8). More than 80% of blindness in all ecological regions was avoidable. Trachoma was a significant cause only in the Sudan savannah belt. The prevalence of all major blinding conditions was highest in the Sahel. CONCLUSIONS The findings of this national survey may be applicable to other countries in West and Central Africa that share similar ecological zones. Onchocerciasis and trachoma are not major causes of blindness in Nigeria, possibly reflecting successful control efforts for both these neglected tropical diseases.

Outcome of Cataract Surgery in Nigeria: Visual Acuity, Autorefraction, and Optimal Intraocular Lens Powers—Results from the Nigeria National Survey

OBJECTIVE To describe presenting and corrected visual acuities after cataract surgery in a nationally representative sample of adults. Another objective was to describe refractive errors in operated eyes and to determine the optimal range of intraocular lens (IOL) powers for this population. DESIGN Cross-sectional, population-based survey. PARTICIPANTS Adults aged 40 years and more were selected using multistage stratified sampling and proportional to size procedures. A sample size of 15027 was calculated, and clusters were selected from all states. METHODS Individuals who had undergone cataract surgery were identified from interview and examination. All had their presenting visual acuity (VA) measured using a reduced logarithm of the minimum angle of resolution chart and underwent autorefraction. Corrected VAs were assessed using the autorefraction results in a trial set. An ophthalmologist conducted all examinations, including slit-lamp and dilated fundus examination. Causes of visual loss were determined for all eyes with a presenting VA <6/12 using the World Health Organization recommendations. Biometry data were derived from 20449 phakic eyes using the SRK-T formula after excluding those with poor VA or corneal opacities. MAIN OUTCOME MEASURES Presenting and corrected visual acuities in pseudo/aphakic individuals and autorefraction findings; biometry profile of Nigerian adults. RESULTS Data from 288 eyes of 217 participants were analyzed. Only 39.5% of eyes had undergone IOL implantation at surgery. Only 29.9% of eyes had a good outcome (i.e., ≥6/18) at presentation, increasing to 55.9% with correction. Use of an IOL was the only factor associated with a good outcome at presentation (odds ratio 9.0; 95% confidence interval, 4.3-18.9; P=0.001). Eyes undergoing cataract surgery had a higher prevalence and degree of astigmatism than phakic eyes. Biometry data reveal that posterior chamber IOL powers of 20, 21, and 22 diopters (D) (A constant 118.0) will give a postoperative refraction range of -2.0 D to emmetropia in 71.4% of eyes, which increases to 82.6% if 19 D is also included. CONCLUSIONS Postoperative astigmatism needs to be reduced through better surgical techniques and training, and use of biometry should be standard of care.

Computerized Repeating and Averaging Improve the Test-Retest Variability of ETDRS Visual Acuity Measurements: Implications for Sensitivity and Specificity

PURPOSE The goals of this study were to investigate the effectiveness of computerized repeating and averaging of visual acuity measurements in reducing test-retest variability (TRV) and to estimate the increase in sensitivity and specificity that would be achieved in diagnosing visual acuity change. METHODS Timed, paired ETDRS chart and computerized acuity mean measurement (CAMM) were performed in 100 subjects. CAMM(n) scores were the running mean of consecutive measurements. Bland-Altman methods were used to calculate 95% ranges for TRV. RESULTS The 95% TRV range of ETDRS measurements and the CAMM score after 6 (CAMM6) measurements were, respectively, 8 and 5.7 ETDRS letters (P = 0.02). CAMM6 offered a pragmatically optimum tradeoff between reduced TRV and test time. A measured change of 5 letters or more in the absence of true change was observed in 13% (95% CI, 8%-21%) with the ETDRS chart and 4% (95% CI, 2%-10%) with CAMM6 measurements. To achieve ≥95% test sensitivity (assuming 95% test specificity), change criteria of 15 and 11 letters must be set with an ETDRS chart and CAMM6, respectively. CAMM6 measurement times were longer (mean 234 seconds vs. 74 seconds) for the ETDRS chart. CONCLUSIONS Compared with the current gold standard, computerized repeating and averaging of acuity measurements improve specificity and sensitivity when identifying true changes. The 160-second increase in test time should be set against the considerable economic and clinical benefits that may result.

Poverty and Blindness in Nigeria: Results from the National Survey of Blindness and Visual Impairment

Abstract Purpose: Poverty can be a cause and consequence of blindness. Some causes only affect the poorest communities (e.g. trachoma), and poor individuals are less likely to access services. In low income countries, cataract blind adults have been shown to be less economically active, indicating that blindness can exacerbate poverty. This study aims to explore associations between poverty and blindness using national survey data from Nigeria. Methods: Participants ≥40 years were examined in 305 clusters (2005–2007). Sociodemographic information, including literacy and occupation, was obtained by interview. Presenting visual acuity (PVA) was assessed using a reduced tumbling E LogMAR chart. Full ocular examination was undertaken by experienced ophthalmologists on all with PVA <6/12 in either eye. Causes of vision loss were determined using World Health Organization guidelines. Households were categorized into three levels of poverty based on literacy and occupation at household level. Results: A total of 569/13,591 participants were blind (PVA <3/60, better eye; prevalence 4.2%, 95% confidence interval [CI] 3.8–4.6%). Prevalences of blindness were 8.5% (95% CI 7.7–9.5%), 2.5% (95% CI 2.0–3.1%), and 1.5% (95% CI 1.2–2.0%) in poorest, medium and affluent households, respectively (p = 0.001). Cause-specific prevalences of blindness from cataract, glaucoma, uncorrected aphakia and corneal opacities were significantly higher in poorer households. Cataract surgical coverage was low (37.2%), being lowest in females in poor households (25.3%). Spectacle coverage was 3 times lower in poor than affluent households (2.4% vs. 7.5%). Conclusion: In Nigeria, blindness is associated with poverty, in part reflecting lower access to services. Reducing avoidable causes will not be achieved unless access to services improves, particularly for the poor and women.