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Outcome of Cataract Surgery in Nigeria: Visual Acuity, Autorefraction, and Optimal Intraocular Lens Powers—Results from the Nigeria National Survey
Outcome of Cataract Surgery in Nigeria: Visual Acuity, Autorefraction, and Optimal Intraocular Lens Powers—Results from the Nigeria National Survey Abdullahi U. Imam, DO, MSc,1 Clare E. Gilbert, FRCOphth, MD,2 Selvaraj Sivasubramaniam, BSc, MSc,2 Gudlavalleti V. S. Murthy, MD, MSc,2 Raj Maini, BM, FRCOphth,3 Mansur M. Rabiu, FMCOphth, MSc,4 on behalf of the Nigeria National Blindness and Visual Impairment Study Group* 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 15 027 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 20 449 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., ⱖ6/18) 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. Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article Ophthalmology 2011;118:719 –724 © 2011 by the American Academy of Ophthalmology. *Group members listed online in Apppendix 1 (available at http://aaojournal.org)
Cataract is the most common cause of blindness worldwide, and cataract surgery is one of the most cost-effective of all interventions.1 The cataract surgical rate (the number of cataract operations performed/million population/year) is increasing in many countries, particularly in Asia and Latin America. However, the cataract surgical rate remains low in Africa, particularly in sub-Saharan Africa, where approximately half of the 57 countries in the World Health Organization’s (WHO) Africa region had a cataract surgical rate of ⬍500 surgeries/million population/year in the year 2006.2 However, it has to be borne in mind that lower life © 2011 by the American Academy of Ophthalmology Published by Elsevier Inc.
expectancies in African countries may also mean that lower cataract surgical rates are needed in Africa to control cataract blindness. Studies across the world have shown that there are many barriers hindering individuals with visually impairing cataract from accessing services, including fear of the operation and of a poor outcome.3–5 There are also many studies demonstrating that visual outcome of cataract surgery is not as good as it could be,6,7 including in Africa.3,8–13 However, the majority of these data were derived from population-based, cross-sectional prevalence studies in which details of preoperative, operative, and postoperative ISSN 0161-6420/11/$–see front matter doi:10.1016/j.ophtha.2010.08.025
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findings were not available, and in which the precise surgical technique could not be ascertained with confidence. In addition, many years may have passed since surgery, and comorbidities may have developed after cataract surgery. This study reports findings from aphakic and pseudophakic participants who were identified during the national survey of visual impairment and blindness in Nigeria.14 To our knowledge, this is the first study to present data on refractive errors and keratometry among a population-based sample of individuals who have undergone cataract surgery and to present biometry data from a nationally representative sample of individuals recruited to a “normative dataset.”
Materials and Methods Details of the methods used in the survey have been published.14 A sample size of 15 027 persons aged ⱖ40 years was calculated on the basis of the target population of 23.6 million people aged ⱖ40 years (or 17.6% of 133 million total Nigerian population, according to a 2005 projected estimate), a blindness prevalence estimate of 5.0%, an absolute precision level of 0.5% with 95% statistical confidence, and further adjusting for a design effect of 1.75% and 15% for non-response. Multi-stage stratified cluster random sampling with probability proportional to size methods was used to identify a cross-sectional, nationally representative sample of the population. Initial stratification was by geopolitical zones, of which there are 6 in Nigeria, followed by stratification by urban/ rural place of residence. A total of 310 clusters, each with 50 adults aged ⱖ40 years, were selected across the country, but 5 were not included because of civil unrest or because village heads did not give permission. These 5 clusters were not replaced.
Examination Examination took place in a temporary clinic set up in each cluster. During an initial interview, the identity of each individual was confirmed against the enumeration lists and the individual’s age was verified using national and local events calendars. Information was collected on language, tribal group, religion and occupation, and water supply and sanitation. Literacy was recorded as could read easily, reads with difficulty, or cannot read. Participants were asked if they had a history of diabetes and whether they had undergone a procedure for cataract surgery (formal cataract surgery or couching, a traditional procedure for cataract) or other ocular treatment. Distance visual acuities (VAs) were measured in each eye by an ophthalmic nurse using a reduced logarithm of the minimum angle of resolution tumbling E chart outside but in a shady area. Acuities were measured unaided, and with distance correction if usually worn. If a participant was unable to see all 3 top letters of the chart at 4 m, the test was repeated at 1 m. If no letters could be seen at this distance in either eye, a study ophthalmologist determined the VA as counting fingers, sees hand movements, perceives light, or no light perception. The participant was assigned a “green” (at least 6/12 in both eyes) or a “red” (⬍6/12 in either eye) card on the basis of the number of letters correctly identified. All participants underwent visual field screening (Frequency Doubling Threshold method, Humphrey Systems, Dublin, CA) and automated refraction with keratometry readings (Takagi ARKM-100, Takagi Seiko, Japan) by an experienced optometrist. Manual refraction was undertaken when autorefraction was not possible. All “red” card participants had their best-corrected VA measured using the auto-refraction findings in a trial frame. All
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participants underwent a basic eye examination by an ophthalmologist; that is, examination of the external eye, lens grading using the Mehra–Minassian method, examination of the optic disc, and determination of the vertical cup:disc ratio. For participants with a history or evidence of cataract surgery or couching, the ophthalmologist documented the length of time since surgery, where surgery took place (i.e., in an eye camp, in a hospital, or at home), and whether aphakic or spectacles for distance were used or not. All were examined at the slit lamp to determine the technique that had been used, that is, couching, or intracapsular or extracapsular cataract surgery, and whether an intraocular lens (IOL) had been inserted. The following participants underwent a more detailed examination: red card holders, those with any abnormality of the disc or fundus, and 1 in every 8 participants regardless of VA. Data from the latter formed the “normative dataset.” Detailed examinations were performed by a second ophthalmologist and included applanation intraocular pressure measurement, using a Goldmann tonometer; axial length measurement using an A scan (Bioline, Rome, Italy), which automatically indicated the most reliable of 3 readings; dilated biomicroscopy at the slit lamp, which included assessment of the posterior capsule in eyes that had undergone cataract surgery; and digital fundus photography. Lens opacities were graded using the WHO Lens Opacity Classification System. In all red card holders, a cause of visual loss was determined for each eye, and one cause was selected to represent the cause for the individual using WHO recommendations. This included individuals with a presenting VA of ⬍6/12 who had undergone cataract surgery.
Quality Assurance Stringent procedures were put in place to ensure quality. This included rigorous training and pilot studies before visiting each of the 6 geopolitical zones, frequent visits to the field by the project manager (MR), repeated interobserver assessment exercises for the main outcomes (i.e., VA, cause of visual loss), and cross-checking of all data forms after entry. Survey equipment, such as the A-scan and autorefractometer, was calibrated regularly. During the survey, the same 4 ophthalmologists undertook the majority of the examinations, and the optometrists were unchanged throughout. For logistic reasons (i.e., language, local culture), ophthalmic nurses and enumerators were recruited and trained for each geopolitical zone.
Ethical Approval The Ethics Committee of the London School of Hygiene and Tropical Medicine approved the study, and The Nigerian National Programme for the Prevention of Blindness of the Federal Ministry of Health provided written ethical approval. Enumerators obtained oral informed consent from the head of the household and each participant after verbal explanation of the procedures to be conducted. Field work for the survey took place between September 2005 and June 2007, with breaks during the rainy season.
Categories of Visual Acuity The WHO has recommended the following definitions of outcome after cataract surgery, which use the presenting VA: “good” (6/18 or better), “borderline” (⬍6/18 to 6/60), and “poor” (⬍6/60). For ease of comparison with other studies, the findings in this report have been converted to Snellen equivalents.15
Imam et al 䡠 Outcome of Cataract Surgery in Nigeria Statistical Analysis Data analysis was carried out using Stata 11.0 (Stata Corp., College Station, TX). Data are presented as numbers, percentages, and medians. Multivariate logistic regression analysis was performed to explore risk factors for poor visual outcome among operated eyes. Models were built using forward stepwise selection for first and second operated eyes separately. The cluster sampling design was taken into account in all the analyses, being reflected in the P values and confidence intervals (CIs). The SRK-T formula was used to determine IOL power calculations, including the range of powers needed to achieve different target postoperative refractive errors.16 K values and axial length from all participants were used after excluding eyes that had undergone a procedure for cataract (i.e., IOL/non-IOL surgery or couching), those with a presenting VA of counting fingers or less, or those with corneal scarring or anterior uveitis because these eyes may not have given reliable axial length or keratometry readings. Extreme outliers (0.5% of data points) were also excluded in the graphic presentation of IOL power needed.
Results A total of 13 591 participants were examined of the 15 122 enumerated, giving a response rate of 89.9%. The response rate ranged from 88.2% to 91.1% in the 6 geopolitical zones. A total of 7031 participants (46.5%) were male, and 77.6% lived in rural areas. A total of 583 eyes had undergone procedures for cataract, in 299 right eyes and 284 left eyes. A total of 148 right eyes were included in the analysis after excluding couching (129 eyes), trauma (21 eyes), and eyes with missing data on the type of surgery (1 eye). A total of 140 left eyes were included after excluding couching (120 eyes), trauma (20 eyes), and missing data (4 eyes). A total of 71 individuals had undergone cataract surgery in both eyes, usually with a similar technique (142 eyes), and 146 individuals had undergone unilateral surgery (total 288 eyes in 217 individuals). It was not possible to determine with any degree of certainty on clinical examination whether eyes had undergone standard extracapsular cataract extraction, small incision surgery, or phacoemulsification. Data on eyes that had been couched will be presented in another publication.17 Overall, only 113 eyes (39.2%) had undergone IOL surgery, but the proportion increased over time, from 11.1% of eyes operated on more than 6 years before the survey to 67.4% of eyes operated on within 3 years of the survey (Fig 1). None of the eyes with an IOL had an anterior chamber IOL.
Figure 1. Change in surgical technique over time. Data missing for 19 eyes. IOL ⫽ intraocular lens.
Table 2. Causes of Visual Loss in Eyes with Presenting Visual Acuity of ⬍ 6/18 (n ⫽ 202) Cause
N
%
Uncorrected aphakia (non-IOL eyes) Refractive error (IOL eyes) Optic atrophy Glaucoma Corneal opacity Posterior subcapsular opacity Phthisis Macular degeneration Other Surgical complication Total
78 22 20 10 8 6 6 5 9 38 202
38.6% 10.9% 9.9% 5.0% 4.0% 3.0% 3.0% 2.5% 4.5% 18.8% 100%
IOL ⫽ intraocular lens.
At presentation, only 29.9% of eyes (86) had a good outcome that improved to 55.9% (161 eyes) with correction (Table 1, available at http://aaojournal.org). A total of 127 eyes (44.1%) had a poor outcome at presentation. With best correction, 33 (26%) of these eyes had a good outcome, 27 (21.2%) improved to borderline, and 67 (52.8%) remained with a poor outcome. In multivariate analysis of data on first-operated eyes, which included demographic characteristics, time of surgery, literacy, and urban/rural place of residence in the model, the only variable associated with poor outcome (⬍6/60 at presentation) was non-IOL surgery, which had a 9-fold higher risk of a poor outcome compared with IOL surgery (odds ratio [OR] 9.0; 95% CI, 4.3–18.9; P⫽0.001). Eyes that had been operated on more than 6 years before the survey also had poorer outcomes, but this was not statistically significant (OR 2.1; 95% CI, 0.9 – 4.8; P⫽0.096). Analysis of second operated eyes showed similar results, with those who were illiterate also having a higher risk of a poor outcome, but this did not reach statistical significance (OR 1.95; 95% CI, 0.9 – 4.2; P⫽0.086). The most common causes of poor outcome were uncorrected refractive error (IOL eyes) and uncorrected aphakia (non-IOL eyes), accounting for half (49.5%) of all poor outcomes (Table 2). Surgical complications (e.g., vitreous loss/incarceration in the wound, corneal decompensation, retinal detachment) were responsible for 18.8% of poor outcomes. Autorefraction data could not be obtained from 12 of 113 pseudophakic eyes (10.6%) and 50 of 159 aphakic eyes (31.4%)
Figure 2. Spherical equivalent in eyes undergoing cataract surgery with or without IOL implantation (diopters). IOL ⫽ intraocular lens.
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Figure 3. Cylindrical refractive error in eyes undergoing cataract surgery with and without IOL implantation and in normal right eyes. IOL ⫽ intraocular lens.
mainly because of poor compliance, but there was also equipment failure in a few clusters. Available data are shown in Figures 2 to 4. The spherical equivalent of eyes that had undergone IOL surgery (Fig 2) ranged from ⫺15 to ⫹15 diopters (D). Overall, 37 of 101 pseudophakic eyes (37%) had a spherical equivalent of more than 2 D of hypermetropia or myopia. The majority of aphakic eyes had spherical equivalents ranging from ⫹9 to ⫹14 D with 21 of 109 eyes (19.3%) having a spherical equivalent of less than ⫹9 D. Astigmatic corrections are shown in Figure 3. The mean cylinder was ⫺1.14 D (standard deviation [SD] 1.0 D) in eyes from the normative database (n ⫽ 1589) but ⫺2.57 D (SD 1.66 D) in pseudophakic eyes and ⫺2.44 D (SD 1.46 D) in aphakic eyes. Pseudophakic eyes with good presenting VA had significantly less astigmatism than eyes with borderline or poor outcomes (P⫽0.028, Wilcoxon rank-sum Mann–Whitney test), but no differences were detected in aphakic eyes. Differences between the minimum and maximum radii of curvature are shown in Figure 3. The mean difference for eyes in the normative database was 0.21 mm (SD 0.39 mm) (n ⫽ 1611) compared with 0.45 mm (SD 0.42 mm) (n ⫽ 104) for pseudophakic eyes and 0.67 mm (SD 0.51 mm) (n ⫽ 136) for aphakic eyes. Biometry data are presented in Table 3 and Figure 5. The mean IOL power (A constant 118.0) needed to achieve a postoperative refractive error of ⫺1.0 D was 20.64 D (SD ⫾ 2.2 D, range 10 –30 D). A standard 19 D IOL would leave the majority of eyes hypermetropic, whereas a standard 21 D would give a median of ⫺1.5 D (interquartile range: ⫺2.5 to ⫺0.34 D). A standard 20 D IOL would give a postoperative refractive error in the range of ⫺2.0 D to emmetropia in 48% of eyes, whereas a 21 D IOL would give this postoperative refraction in 43% of eyes. If biometry data were available but only a limited stock of IOLs could be maintained, then IOLs with the powers 20, 21, and 22 D would be optimal, assuming an A constant of 118.0 for a posterior chamber lens, giving a postoperative refraction in the range of ⫺2.0 D to emmetropia in 71.4% of eyes.
studies with disaggregated data demonstrate that IOL surgery gives far better presenting visual acuities than non-IOL surgery: an unknown number of eyes without IOLs may have had complicated surgery, and so an IOL was not inserted. The study also supports the findings of other small surveys undertaken in northern Nigeria, which have also demonstrated high rates of couching.13 Reasons for this were not explored in this study, but lack of access to affordable cataract surgical services is likely to be one explanation.17 It has to be borne in mind that in cross-sectional surveys, the surgery may have been conducted many years earlier; thus, it is not possible to determine the sequence of events, and preoperative and operative findings (e.g., details of the type of surgery) are not available. As in all other studies, individuals who had undergone IOL surgery had far better VAs both before and after correction than those who were aphakic. In Nigeria, there is evidence of a trend toward an increase in IOL surgery, but approximately 1 in 3 cataract operations performed within the last 3 years were still non-IOL. This information may be subject to recall bias, however, because participants were asked to indicate how long ago cataract surgery had been performed and some individuals may have had second eye, non-IOL surgery within the last 3 years because the first eye was already aphakic. Another reason for the low rate of IOL surgery is cost, because patients are often asked to pay for their own consumables in Nigeria. If patients are not aware of the benefits of IOL surgery, they may not be willing to pay the additional cost for an IOL. Another limitation of this study was that biometry data were not obtained from all eyes because of a combination of some participants being too old or uncooperative, the equipment failed in a few clusters, and data could not be obtained from eyes with corneal scarring. To our knowledge, this is the first population-based survey to present autorefraction data after cataract surgery in a developing country and the first population-based study of biometry in Africa. The findings indicate that more attention needs to be given to preoperative biometry, with insertion of an appropriate power IOL. In this setting, if only a range of IOL powers are available, then ⫹20 and
Discussion The findings of this national survey are similar to the findings of many other population-based studies from developing countries (Table 4, available at http://aaojournal. org)23-33 where poor outcomes (using presenting VA) range from 12% in the Philippines to 64% in Cameroon. All
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Figure 4. Differences between radii of curvature in eyes undergoing cataract surgery with and without IOL implantation and in normal right eyes. IOL ⫽ intraocular lens; R1, R2 ⫽ radii of curvature.
Imam et al 䡠 Outcome of Cataract Surgery in Nigeria Table 3. Results of Biometry Using the SRK-T Formula (n ⫽ 20,449 eyes) IOL Power
Hypermetropic (%)
Median (D)
Interquartile Range (D)
Between ⴚ2.0 and 0 D (%)
19 D 20 D 21 D
⬎50% ⬎25% ⬎10%
⫹0.21 ⫺0.64 ⫺1.5 D
⫺0.77 to ⫹1.32 ⫺1.63 to ⫹0.50 ⫺2.52 to ⫺0.34
38% 48% 43%
D ⫽ diopters; IOL ⫽ intraocular lens.
⫹21 D (with an A constant of 118.0) would seem to be the most appropriate. However, if these powers were to be used routinely without biometry, at least 50% of eyes would have a postoperative refraction outside the range of ⫺2.0 D to emmetropia. Biometry is, therefore, to be encouraged, and this may require additional equipment and training, and changes in practices with regard to ordering and stock control. All have cost and managerial implications that pose challenges in Africa, where management of eyecare services is not always adequate and ophthalmologists are not always the key decision makers. Another option to increase the range of IOL powers readily available would be the establishment of IOL manufacture within the country. The high levels of astigmatism among pseudo/aphakic participants in this survey also indicate that more attention needs to be given to preparation of the incision during surgery and to wound suturing. These aspects need to be highlighted and monitored during training, and surgeons should be encouraged to audit and monitor the results of their own surgery so they can take the steps necessary to improve their own outcomes.18 Providers should ensure that all surgeons have adequate equipment (e.g., anterior vitrectomy machines to manage vitreous loss) and high-quality surgical instruments and consumables to be able to perform microsurgery. Small incision cataract surgery should reduce postoperative astigmatism as long as a watertight sclera tunnel is fashioned. Indeed, it has been shown within the context of clinical trials that the degree of astigmatism after small incision cataract surgery is no greater at 6 months than
Figure 5. IOL power (posterior chamber) needed to give a target postoperative refractive error of 0 D (above) and ⫺1.0 D (below). IOL ⫽ intraocular lens; PostOp Ref ⫽ postoperative refraction; D ⫽ diopters.
after phacoemulsification.19 Small incision surgery should, therefore, not only give better short- and long-term visual outcomes but also cost less for the provider and patients.20 Training in small incision cataract surgery for those who qualified before this technique became widespread would increase surgical skills, and residency programs should emphasize the importance of careful case selection, with counseling of patients with other ocular comorbidities. In conclusion, cataract is the most common cause of blindness worldwide (⬍3/60 in the better eye) and accounts for more than 40% of blindness in Nigeria.21 In Asia, high-quality cataract surgery (i.e., IOL surgery) at affordable prices generates demand for surgery and increases the cataract surgical rate.22 In Nigeria, greater emphasis needs to be placed on quality so that potential patients will be willing to invest their scarce resources in cataract surgery.
References 1. Lansingh VC, Carter MJ, Martens M. Global cost-effectiveness of cataract surgery. Ophthalmology 2007;114:1670 – 8. 2. World Health Organization. Prevention of Blindness and Visual Impairment. Data and Maps: 2006 Cataract Surgical Rate Table. Available at: http://www.who.int/blindness/CSR%202006.pdf. Accessed February 25, 2010. 3. Yorston D, Abiose A. Cataract blindness—the African perspective. Bull World Health Organ 2001;79:257– 8. 4. Chang MA, Congdon NG, Baker SK, et al. The surgical management of cataract: barriers, best practices and outcomes. Int Ophthalmol 2008;28:247– 60. 5. Finger RP. Cataracts in India: current situation, access, and barriers to services over time. Ophthalmic Epidemiol 2007; 14:112– 8. 6. Limburg H, Silva JC, Foster A. Cataract in Latin America: findings from nine recent surveys. Rev Panam Salud Publica 2009;25:449 –55. 7. Walia T, Yorston D. Improving surgical outcomes. Community Eye Health 2008;21:58 –9. 8. Bejiga A, Tadesse S. Cataract surgical coverage and outcome in Goro District, Central Ethiopia. Ethiop Med J 2008;46:205–10. 9. Mathenge W, Nkurikiye J, Limburg H, Kuper H. Rapid assessment of avoidable blindness in Western Rwanda: blindness in a postconflict setting [report online]. PLoS Med 2007;4:e217. Available at: http://www.plosmedicine.org/article/info%3Adoi%2F10.1371% 2Fjournal.pmed.0040217. Accessed February 25, 2010. 10. Oye JE, Kuper H. Prevalence and causes of blindness and visual impairment in Limbe urban area, South West Province, Cameroon. Br J Ophthalmol 2007;91:1435–9. 11. Oye JE, Kuper H, Dineen B, et al. Prevalence and causes of blindness and visual impairment in Muyuka: a rural health
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district in South West Province, Cameroon. Br J Ophthalmol 2006;90:538 – 42. Rabiu MM. Cataract blindness and barriers to uptake of cataract surgery in a rural community of northern Nigeria. Br J Ophthalmol 2001;85:776 – 80. Rabiu MM, Muhammed N. Rapid assessment of cataract surgical services in Birnin-Kebbi local government area of Kebbi State, Nigeria. Ophthalmic Epidemiol 2008;15:359–65. Dineen B, Gilbert C, Rabiu MM, et al. The Nigerian national blindness and visual impairment survey: rationale, objectives and detailed methodology. BMC Ophthalmol [serial online] 2008;8:17. Available at: http://www.biomedcentral.com/ 1471-2415/8/17. Accessed February 25, 2010. Programme for the Prevention of Blindness and Deafness. Informal consultation on analysis of blindness prevention outcomes. Geneva, Switzerland: World Health Organization; 1998. WHO/PBL/98.68. Available at: http://whqlibdoc.who. int/hq/1998/WHO_PBL_98.68.pdf. Accessed August 7, 2010. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990;16:333– 40. Gilbert CE, Murthy GV, Selvaraj S, et al. Couching in Nigeria: prevalence, risk factors and visual acuity outcomes. Ophthalmic Epidemiol 2010;117:269-75. Limburg H, Foster A, Gilbert C, et al. Routine monitoring of visual outcome of cataract surgery. Part 1: Development of an instrument. Br J Ophthalmol 2005;89:45–9. Gogate PM, Kulkarni SR, Krishnaiah S, et al. Safety and efficacy of phacoemulsification compared with manual smallincision cataract surgery by a randomized controlled clinical trial: six-week results. Ophthalmology 2005;112:869 –74. Gogate PM. Small incision cataract surgery: complications and mini-review. Indian J Ophthalmol 2009;57:45–9. Abdull MM, Sivasubramaniam S, Murthy GV, et al, Nigeria National Blindness and Visual Impairment Study Group. Causes of blindness and visual impairment in Nigeria: the Nigeria National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci 2009;50:4114 –20. Lewallen S, Thulasiraj RD. Eliminating cataract blindness— how do we apply lessons from Asia to sub-Saharan Africa? Glob Public Health 2010;10:1–10.
23. Amansakhatov S, Volokhovskaya ZP, Afanasyeva AN, Limburg H. Cataract blindness in Turkmenistan: results of a national survey. Br J Ophthalmol 2002;86:1207–10. 24. Bourne RR, Dineen BP, Ali SM, et al. Outcomes of cataract surgery in Bangladesh: results from a population based nationwide survey. Br J Ophthalmol 2003;87:813–9. 25. Bourne R, Dineen B, Jadoon Z, et al. Outcomes of cataract surgery in Pakistan: results from the Pakistan National Blindness and Visual Impairment Survey. Br J Ophthalmol 2007; 91:420 – 6. 26. Mathenge W, Kuper H, Limburg H, et al. Rapid assessment of avoidable blindness in Nakuru district, Kenya. Ophthalmology 2007;114:599 – 605. 27. Courtright P, Metcalfe N, Hoechsmann A, et al, Chikwawa Survey Team. Cataract surgical coverage and outcome of cataract surgery in a rural district in Malawi. Can J Ophthalmol 2004;39:25–30. 28. Lindfield R, Polack S, Wadud Z, et al. Causes of poor outcome after cataract surgery in Satkhira district, Bangladesh. Eye (Lond) 2008;22:1054 – 6. 29. Nirmalan PK, Thulasiraj RD, Maneksha V, et al. A population based eye survey of older adults in Tirunelveli district of south India: blindness, cataract surgery, and visual outcomes. Br J Ophthalmol 2002;86:505–12. 30. Murthy GV, Vashist P, John N, et al. Prevalence and visionrelated outcomes of cataract surgery in Gujarat, India. Ophthalmic Epidemiol 2009;16:400 –9. 31. National Survey on Blindness and Visual Outcomes after Cataract Surgery (2001-2002). New Delhi, India: National Program for Control of Blindness, Ministry of Health Family Welfare, Govt. of India; 2002: 88-92. Available at: http:// www.vision2020india.org/downloads/National_Survey_on_ Blindness_and_Visual_Outcomes_after_Cataract_Surgery_NPCB. pdf. Accessed August 7, 2010. 32. Eusebio C, Kuper H, Polack S, et al. Rapid assessment of avoidable blindness in Negros Island and Antique District, Philippines. Br J Ophthalmol 2007;91:1588 –92. 33. Bassett KL, Noertjojo K, Liu L, et al. Cataract surgical coverage and outcome in the Tibet Autonomous Region of China. Br J Ophthalmol 2005;89:5–9.
Footnotes and Financial Disclosures Originally received: April 1, 2010. Final revision: July 20, 2010. Accepted: August 11, 2010. Available online: November 4, 2010. 1
Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Manuscript no. 2010-479.
Ministry of Health Minna, Niger State, Nigeria.
2
International Centre for Eye Health, London School of Hygiene and Tropical Medicine, London, United Kingdom.
3
Moorfields Eye Hospital, London, United Kingdom.
4
National Eye Centre Kaduna, Nigeria.
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This study was funded by CBM, Sightsavers International, and Velux Stiftung. Correspondence: Gudlavalleti V. S. Murthy, MD, MSc, International Centre for Eye Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT. E-mail: [email protected]. *The Nigeria National Blindness and Visual Impairment Study Group is available at http://aaojournal.org.
Cataract is the most common cause of blindness worldwide, and cataract surgery is one of the most cost-effective of all interventions.1 The cataract surgical rate (the number of cataract operations performed/million population/year) is increasing in many countries, particularly in Asia and Latin America. However, the cataract surgical rate remains low in Africa, particularly in sub-Saharan Africa, where approximately half of the 57 countries in the World Health Organization’s (WHO) Africa region had a cataract surgical rate of ⬍500 surgeries/million population/year in the year 2006.2 However, it has to be borne in mind that lower life © 2011 by the American Academy of Ophthalmology Published by Elsevier Inc.
expectancies in African countries may also mean that lower cataract surgical rates are needed in Africa to control cataract blindness. Studies across the world have shown that there are many barriers hindering individuals with visually impairing cataract from accessing services, including fear of the operation and of a poor outcome.3–5 There are also many studies demonstrating that visual outcome of cataract surgery is not as good as it could be,6,7 including in Africa.3,8–13 However, the majority of these data were derived from population-based, cross-sectional prevalence studies in which details of preoperative, operative, and postoperative ISSN 0161-6420/11/$–see front matter doi:10.1016/j.ophtha.2010.08.025
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findings were not available, and in which the precise surgical technique could not be ascertained with confidence. In addition, many years may have passed since surgery, and comorbidities may have developed after cataract surgery. This study reports findings from aphakic and pseudophakic participants who were identified during the national survey of visual impairment and blindness in Nigeria.14 To our knowledge, this is the first study to present data on refractive errors and keratometry among a population-based sample of individuals who have undergone cataract surgery and to present biometry data from a nationally representative sample of individuals recruited to a “normative dataset.”
Materials and Methods Details of the methods used in the survey have been published.14 A sample size of 15 027 persons aged ⱖ40 years was calculated on the basis of the target population of 23.6 million people aged ⱖ40 years (or 17.6% of 133 million total Nigerian population, according to a 2005 projected estimate), a blindness prevalence estimate of 5.0%, an absolute precision level of 0.5% with 95% statistical confidence, and further adjusting for a design effect of 1.75% and 15% for non-response. Multi-stage stratified cluster random sampling with probability proportional to size methods was used to identify a cross-sectional, nationally representative sample of the population. Initial stratification was by geopolitical zones, of which there are 6 in Nigeria, followed by stratification by urban/ rural place of residence. A total of 310 clusters, each with 50 adults aged ⱖ40 years, were selected across the country, but 5 were not included because of civil unrest or because village heads did not give permission. These 5 clusters were not replaced.
Examination Examination took place in a temporary clinic set up in each cluster. During an initial interview, the identity of each individual was confirmed against the enumeration lists and the individual’s age was verified using national and local events calendars. Information was collected on language, tribal group, religion and occupation, and water supply and sanitation. Literacy was recorded as could read easily, reads with difficulty, or cannot read. Participants were asked if they had a history of diabetes and whether they had undergone a procedure for cataract surgery (formal cataract surgery or couching, a traditional procedure for cataract) or other ocular treatment. Distance visual acuities (VAs) were measured in each eye by an ophthalmic nurse using a reduced logarithm of the minimum angle of resolution tumbling E chart outside but in a shady area. Acuities were measured unaided, and with distance correction if usually worn. If a participant was unable to see all 3 top letters of the chart at 4 m, the test was repeated at 1 m. If no letters could be seen at this distance in either eye, a study ophthalmologist determined the VA as counting fingers, sees hand movements, perceives light, or no light perception. The participant was assigned a “green” (at least 6/12 in both eyes) or a “red” (⬍6/12 in either eye) card on the basis of the number of letters correctly identified. All participants underwent visual field screening (Frequency Doubling Threshold method, Humphrey Systems, Dublin, CA) and automated refraction with keratometry readings (Takagi ARKM-100, Takagi Seiko, Japan) by an experienced optometrist. Manual refraction was undertaken when autorefraction was not possible. All “red” card participants had their best-corrected VA measured using the auto-refraction findings in a trial frame. All
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participants underwent a basic eye examination by an ophthalmologist; that is, examination of the external eye, lens grading using the Mehra–Minassian method, examination of the optic disc, and determination of the vertical cup:disc ratio. For participants with a history or evidence of cataract surgery or couching, the ophthalmologist documented the length of time since surgery, where surgery took place (i.e., in an eye camp, in a hospital, or at home), and whether aphakic or spectacles for distance were used or not. All were examined at the slit lamp to determine the technique that had been used, that is, couching, or intracapsular or extracapsular cataract surgery, and whether an intraocular lens (IOL) had been inserted. The following participants underwent a more detailed examination: red card holders, those with any abnormality of the disc or fundus, and 1 in every 8 participants regardless of VA. Data from the latter formed the “normative dataset.” Detailed examinations were performed by a second ophthalmologist and included applanation intraocular pressure measurement, using a Goldmann tonometer; axial length measurement using an A scan (Bioline, Rome, Italy), which automatically indicated the most reliable of 3 readings; dilated biomicroscopy at the slit lamp, which included assessment of the posterior capsule in eyes that had undergone cataract surgery; and digital fundus photography. Lens opacities were graded using the WHO Lens Opacity Classification System. In all red card holders, a cause of visual loss was determined for each eye, and one cause was selected to represent the cause for the individual using WHO recommendations. This included individuals with a presenting VA of ⬍6/12 who had undergone cataract surgery.
Quality Assurance Stringent procedures were put in place to ensure quality. This included rigorous training and pilot studies before visiting each of the 6 geopolitical zones, frequent visits to the field by the project manager (MR), repeated interobserver assessment exercises for the main outcomes (i.e., VA, cause of visual loss), and cross-checking of all data forms after entry. Survey equipment, such as the A-scan and autorefractometer, was calibrated regularly. During the survey, the same 4 ophthalmologists undertook the majority of the examinations, and the optometrists were unchanged throughout. For logistic reasons (i.e., language, local culture), ophthalmic nurses and enumerators were recruited and trained for each geopolitical zone.
Ethical Approval The Ethics Committee of the London School of Hygiene and Tropical Medicine approved the study, and The Nigerian National Programme for the Prevention of Blindness of the Federal Ministry of Health provided written ethical approval. Enumerators obtained oral informed consent from the head of the household and each participant after verbal explanation of the procedures to be conducted. Field work for the survey took place between September 2005 and June 2007, with breaks during the rainy season.
Categories of Visual Acuity The WHO has recommended the following definitions of outcome after cataract surgery, which use the presenting VA: “good” (6/18 or better), “borderline” (⬍6/18 to 6/60), and “poor” (⬍6/60). For ease of comparison with other studies, the findings in this report have been converted to Snellen equivalents.15
Imam et al 䡠 Outcome of Cataract Surgery in Nigeria Statistical Analysis Data analysis was carried out using Stata 11.0 (Stata Corp., College Station, TX). Data are presented as numbers, percentages, and medians. Multivariate logistic regression analysis was performed to explore risk factors for poor visual outcome among operated eyes. Models were built using forward stepwise selection for first and second operated eyes separately. The cluster sampling design was taken into account in all the analyses, being reflected in the P values and confidence intervals (CIs). The SRK-T formula was used to determine IOL power calculations, including the range of powers needed to achieve different target postoperative refractive errors.16 K values and axial length from all participants were used after excluding eyes that had undergone a procedure for cataract (i.e., IOL/non-IOL surgery or couching), those with a presenting VA of counting fingers or less, or those with corneal scarring or anterior uveitis because these eyes may not have given reliable axial length or keratometry readings. Extreme outliers (0.5% of data points) were also excluded in the graphic presentation of IOL power needed.
Results A total of 13 591 participants were examined of the 15 122 enumerated, giving a response rate of 89.9%. The response rate ranged from 88.2% to 91.1% in the 6 geopolitical zones. A total of 7031 participants (46.5%) were male, and 77.6% lived in rural areas. A total of 583 eyes had undergone procedures for cataract, in 299 right eyes and 284 left eyes. A total of 148 right eyes were included in the analysis after excluding couching (129 eyes), trauma (21 eyes), and eyes with missing data on the type of surgery (1 eye). A total of 140 left eyes were included after excluding couching (120 eyes), trauma (20 eyes), and missing data (4 eyes). A total of 71 individuals had undergone cataract surgery in both eyes, usually with a similar technique (142 eyes), and 146 individuals had undergone unilateral surgery (total 288 eyes in 217 individuals). It was not possible to determine with any degree of certainty on clinical examination whether eyes had undergone standard extracapsular cataract extraction, small incision surgery, or phacoemulsification. Data on eyes that had been couched will be presented in another publication.17 Overall, only 113 eyes (39.2%) had undergone IOL surgery, but the proportion increased over time, from 11.1% of eyes operated on more than 6 years before the survey to 67.4% of eyes operated on within 3 years of the survey (Fig 1). None of the eyes with an IOL had an anterior chamber IOL.
Figure 1. Change in surgical technique over time. Data missing for 19 eyes. IOL ⫽ intraocular lens.
Table 2. Causes of Visual Loss in Eyes with Presenting Visual Acuity of ⬍ 6/18 (n ⫽ 202) Cause
N
%
Uncorrected aphakia (non-IOL eyes) Refractive error (IOL eyes) Optic atrophy Glaucoma Corneal opacity Posterior subcapsular opacity Phthisis Macular degeneration Other Surgical complication Total
78 22 20 10 8 6 6 5 9 38 202
38.6% 10.9% 9.9% 5.0% 4.0% 3.0% 3.0% 2.5% 4.5% 18.8% 100%
IOL ⫽ intraocular lens.
At presentation, only 29.9% of eyes (86) had a good outcome that improved to 55.9% (161 eyes) with correction (Table 1, available at http://aaojournal.org). A total of 127 eyes (44.1%) had a poor outcome at presentation. With best correction, 33 (26%) of these eyes had a good outcome, 27 (21.2%) improved to borderline, and 67 (52.8%) remained with a poor outcome. In multivariate analysis of data on first-operated eyes, which included demographic characteristics, time of surgery, literacy, and urban/rural place of residence in the model, the only variable associated with poor outcome (⬍6/60 at presentation) was non-IOL surgery, which had a 9-fold higher risk of a poor outcome compared with IOL surgery (odds ratio [OR] 9.0; 95% CI, 4.3–18.9; P⫽0.001). Eyes that had been operated on more than 6 years before the survey also had poorer outcomes, but this was not statistically significant (OR 2.1; 95% CI, 0.9 – 4.8; P⫽0.096). Analysis of second operated eyes showed similar results, with those who were illiterate also having a higher risk of a poor outcome, but this did not reach statistical significance (OR 1.95; 95% CI, 0.9 – 4.2; P⫽0.086). The most common causes of poor outcome were uncorrected refractive error (IOL eyes) and uncorrected aphakia (non-IOL eyes), accounting for half (49.5%) of all poor outcomes (Table 2). Surgical complications (e.g., vitreous loss/incarceration in the wound, corneal decompensation, retinal detachment) were responsible for 18.8% of poor outcomes. Autorefraction data could not be obtained from 12 of 113 pseudophakic eyes (10.6%) and 50 of 159 aphakic eyes (31.4%)
Figure 2. Spherical equivalent in eyes undergoing cataract surgery with or without IOL implantation (diopters). IOL ⫽ intraocular lens.
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Figure 3. Cylindrical refractive error in eyes undergoing cataract surgery with and without IOL implantation and in normal right eyes. IOL ⫽ intraocular lens.
mainly because of poor compliance, but there was also equipment failure in a few clusters. Available data are shown in Figures 2 to 4. The spherical equivalent of eyes that had undergone IOL surgery (Fig 2) ranged from ⫺15 to ⫹15 diopters (D). Overall, 37 of 101 pseudophakic eyes (37%) had a spherical equivalent of more than 2 D of hypermetropia or myopia. The majority of aphakic eyes had spherical equivalents ranging from ⫹9 to ⫹14 D with 21 of 109 eyes (19.3%) having a spherical equivalent of less than ⫹9 D. Astigmatic corrections are shown in Figure 3. The mean cylinder was ⫺1.14 D (standard deviation [SD] 1.0 D) in eyes from the normative database (n ⫽ 1589) but ⫺2.57 D (SD 1.66 D) in pseudophakic eyes and ⫺2.44 D (SD 1.46 D) in aphakic eyes. Pseudophakic eyes with good presenting VA had significantly less astigmatism than eyes with borderline or poor outcomes (P⫽0.028, Wilcoxon rank-sum Mann–Whitney test), but no differences were detected in aphakic eyes. Differences between the minimum and maximum radii of curvature are shown in Figure 3. The mean difference for eyes in the normative database was 0.21 mm (SD 0.39 mm) (n ⫽ 1611) compared with 0.45 mm (SD 0.42 mm) (n ⫽ 104) for pseudophakic eyes and 0.67 mm (SD 0.51 mm) (n ⫽ 136) for aphakic eyes. Biometry data are presented in Table 3 and Figure 5. The mean IOL power (A constant 118.0) needed to achieve a postoperative refractive error of ⫺1.0 D was 20.64 D (SD ⫾ 2.2 D, range 10 –30 D). A standard 19 D IOL would leave the majority of eyes hypermetropic, whereas a standard 21 D would give a median of ⫺1.5 D (interquartile range: ⫺2.5 to ⫺0.34 D). A standard 20 D IOL would give a postoperative refractive error in the range of ⫺2.0 D to emmetropia in 48% of eyes, whereas a 21 D IOL would give this postoperative refraction in 43% of eyes. If biometry data were available but only a limited stock of IOLs could be maintained, then IOLs with the powers 20, 21, and 22 D would be optimal, assuming an A constant of 118.0 for a posterior chamber lens, giving a postoperative refraction in the range of ⫺2.0 D to emmetropia in 71.4% of eyes.
studies with disaggregated data demonstrate that IOL surgery gives far better presenting visual acuities than non-IOL surgery: an unknown number of eyes without IOLs may have had complicated surgery, and so an IOL was not inserted. The study also supports the findings of other small surveys undertaken in northern Nigeria, which have also demonstrated high rates of couching.13 Reasons for this were not explored in this study, but lack of access to affordable cataract surgical services is likely to be one explanation.17 It has to be borne in mind that in cross-sectional surveys, the surgery may have been conducted many years earlier; thus, it is not possible to determine the sequence of events, and preoperative and operative findings (e.g., details of the type of surgery) are not available. As in all other studies, individuals who had undergone IOL surgery had far better VAs both before and after correction than those who were aphakic. In Nigeria, there is evidence of a trend toward an increase in IOL surgery, but approximately 1 in 3 cataract operations performed within the last 3 years were still non-IOL. This information may be subject to recall bias, however, because participants were asked to indicate how long ago cataract surgery had been performed and some individuals may have had second eye, non-IOL surgery within the last 3 years because the first eye was already aphakic. Another reason for the low rate of IOL surgery is cost, because patients are often asked to pay for their own consumables in Nigeria. If patients are not aware of the benefits of IOL surgery, they may not be willing to pay the additional cost for an IOL. Another limitation of this study was that biometry data were not obtained from all eyes because of a combination of some participants being too old or uncooperative, the equipment failed in a few clusters, and data could not be obtained from eyes with corneal scarring. To our knowledge, this is the first population-based survey to present autorefraction data after cataract surgery in a developing country and the first population-based study of biometry in Africa. The findings indicate that more attention needs to be given to preoperative biometry, with insertion of an appropriate power IOL. In this setting, if only a range of IOL powers are available, then ⫹20 and
Discussion The findings of this national survey are similar to the findings of many other population-based studies from developing countries (Table 4, available at http://aaojournal. org)23-33 where poor outcomes (using presenting VA) range from 12% in the Philippines to 64% in Cameroon. All
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Figure 4. Differences between radii of curvature in eyes undergoing cataract surgery with and without IOL implantation and in normal right eyes. IOL ⫽ intraocular lens; R1, R2 ⫽ radii of curvature.
Imam et al 䡠 Outcome of Cataract Surgery in Nigeria Table 3. Results of Biometry Using the SRK-T Formula (n ⫽ 20,449 eyes) IOL Power
Hypermetropic (%)
Median (D)
Interquartile Range (D)
Between ⴚ2.0 and 0 D (%)
19 D 20 D 21 D
⬎50% ⬎25% ⬎10%
⫹0.21 ⫺0.64 ⫺1.5 D
⫺0.77 to ⫹1.32 ⫺1.63 to ⫹0.50 ⫺2.52 to ⫺0.34
38% 48% 43%
D ⫽ diopters; IOL ⫽ intraocular lens.
⫹21 D (with an A constant of 118.0) would seem to be the most appropriate. However, if these powers were to be used routinely without biometry, at least 50% of eyes would have a postoperative refraction outside the range of ⫺2.0 D to emmetropia. Biometry is, therefore, to be encouraged, and this may require additional equipment and training, and changes in practices with regard to ordering and stock control. All have cost and managerial implications that pose challenges in Africa, where management of eyecare services is not always adequate and ophthalmologists are not always the key decision makers. Another option to increase the range of IOL powers readily available would be the establishment of IOL manufacture within the country. The high levels of astigmatism among pseudo/aphakic participants in this survey also indicate that more attention needs to be given to preparation of the incision during surgery and to wound suturing. These aspects need to be highlighted and monitored during training, and surgeons should be encouraged to audit and monitor the results of their own surgery so they can take the steps necessary to improve their own outcomes.18 Providers should ensure that all surgeons have adequate equipment (e.g., anterior vitrectomy machines to manage vitreous loss) and high-quality surgical instruments and consumables to be able to perform microsurgery. Small incision cataract surgery should reduce postoperative astigmatism as long as a watertight sclera tunnel is fashioned. Indeed, it has been shown within the context of clinical trials that the degree of astigmatism after small incision cataract surgery is no greater at 6 months than
Figure 5. IOL power (posterior chamber) needed to give a target postoperative refractive error of 0 D (above) and ⫺1.0 D (below). IOL ⫽ intraocular lens; PostOp Ref ⫽ postoperative refraction; D ⫽ diopters.
after phacoemulsification.19 Small incision surgery should, therefore, not only give better short- and long-term visual outcomes but also cost less for the provider and patients.20 Training in small incision cataract surgery for those who qualified before this technique became widespread would increase surgical skills, and residency programs should emphasize the importance of careful case selection, with counseling of patients with other ocular comorbidities. In conclusion, cataract is the most common cause of blindness worldwide (⬍3/60 in the better eye) and accounts for more than 40% of blindness in Nigeria.21 In Asia, high-quality cataract surgery (i.e., IOL surgery) at affordable prices generates demand for surgery and increases the cataract surgical rate.22 In Nigeria, greater emphasis needs to be placed on quality so that potential patients will be willing to invest their scarce resources in cataract surgery.
References 1. Lansingh VC, Carter MJ, Martens M. Global cost-effectiveness of cataract surgery. Ophthalmology 2007;114:1670 – 8. 2. World Health Organization. Prevention of Blindness and Visual Impairment. Data and Maps: 2006 Cataract Surgical Rate Table. Available at: http://www.who.int/blindness/CSR%202006.pdf. Accessed February 25, 2010. 3. Yorston D, Abiose A. Cataract blindness—the African perspective. Bull World Health Organ 2001;79:257– 8. 4. Chang MA, Congdon NG, Baker SK, et al. The surgical management of cataract: barriers, best practices and outcomes. Int Ophthalmol 2008;28:247– 60. 5. Finger RP. Cataracts in India: current situation, access, and barriers to services over time. Ophthalmic Epidemiol 2007; 14:112– 8. 6. Limburg H, Silva JC, Foster A. Cataract in Latin America: findings from nine recent surveys. Rev Panam Salud Publica 2009;25:449 –55. 7. Walia T, Yorston D. Improving surgical outcomes. Community Eye Health 2008;21:58 –9. 8. Bejiga A, Tadesse S. Cataract surgical coverage and outcome in Goro District, Central Ethiopia. Ethiop Med J 2008;46:205–10. 9. Mathenge W, Nkurikiye J, Limburg H, Kuper H. Rapid assessment of avoidable blindness in Western Rwanda: blindness in a postconflict setting [report online]. PLoS Med 2007;4:e217. Available at: http://www.plosmedicine.org/article/info%3Adoi%2F10.1371% 2Fjournal.pmed.0040217. Accessed February 25, 2010. 10. Oye JE, Kuper H. Prevalence and causes of blindness and visual impairment in Limbe urban area, South West Province, Cameroon. Br J Ophthalmol 2007;91:1435–9. 11. Oye JE, Kuper H, Dineen B, et al. Prevalence and causes of blindness and visual impairment in Muyuka: a rural health
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district in South West Province, Cameroon. Br J Ophthalmol 2006;90:538 – 42. Rabiu MM. Cataract blindness and barriers to uptake of cataract surgery in a rural community of northern Nigeria. Br J Ophthalmol 2001;85:776 – 80. Rabiu MM, Muhammed N. Rapid assessment of cataract surgical services in Birnin-Kebbi local government area of Kebbi State, Nigeria. Ophthalmic Epidemiol 2008;15:359–65. Dineen B, Gilbert C, Rabiu MM, et al. The Nigerian national blindness and visual impairment survey: rationale, objectives and detailed methodology. BMC Ophthalmol [serial online] 2008;8:17. Available at: http://www.biomedcentral.com/ 1471-2415/8/17. Accessed February 25, 2010. Programme for the Prevention of Blindness and Deafness. Informal consultation on analysis of blindness prevention outcomes. Geneva, Switzerland: World Health Organization; 1998. WHO/PBL/98.68. Available at: http://whqlibdoc.who. int/hq/1998/WHO_PBL_98.68.pdf. Accessed August 7, 2010. Retzlaff JA, Sanders DR, Kraff MC. Development of the SRK/T intraocular lens implant power calculation formula. J Cataract Refract Surg 1990;16:333– 40. Gilbert CE, Murthy GV, Selvaraj S, et al. Couching in Nigeria: prevalence, risk factors and visual acuity outcomes. Ophthalmic Epidemiol 2010;117:269-75. Limburg H, Foster A, Gilbert C, et al. Routine monitoring of visual outcome of cataract surgery. Part 1: Development of an instrument. Br J Ophthalmol 2005;89:45–9. Gogate PM, Kulkarni SR, Krishnaiah S, et al. Safety and efficacy of phacoemulsification compared with manual smallincision cataract surgery by a randomized controlled clinical trial: six-week results. Ophthalmology 2005;112:869 –74. Gogate PM. Small incision cataract surgery: complications and mini-review. Indian J Ophthalmol 2009;57:45–9. Abdull MM, Sivasubramaniam S, Murthy GV, et al, Nigeria National Blindness and Visual Impairment Study Group. Causes of blindness and visual impairment in Nigeria: the Nigeria National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci 2009;50:4114 –20. Lewallen S, Thulasiraj RD. Eliminating cataract blindness— how do we apply lessons from Asia to sub-Saharan Africa? Glob Public Health 2010;10:1–10.
23. Amansakhatov S, Volokhovskaya ZP, Afanasyeva AN, Limburg H. Cataract blindness in Turkmenistan: results of a national survey. Br J Ophthalmol 2002;86:1207–10. 24. Bourne RR, Dineen BP, Ali SM, et al. Outcomes of cataract surgery in Bangladesh: results from a population based nationwide survey. Br J Ophthalmol 2003;87:813–9. 25. Bourne R, Dineen B, Jadoon Z, et al. Outcomes of cataract surgery in Pakistan: results from the Pakistan National Blindness and Visual Impairment Survey. Br J Ophthalmol 2007; 91:420 – 6. 26. Mathenge W, Kuper H, Limburg H, et al. Rapid assessment of avoidable blindness in Nakuru district, Kenya. Ophthalmology 2007;114:599 – 605. 27. Courtright P, Metcalfe N, Hoechsmann A, et al, Chikwawa Survey Team. Cataract surgical coverage and outcome of cataract surgery in a rural district in Malawi. Can J Ophthalmol 2004;39:25–30. 28. Lindfield R, Polack S, Wadud Z, et al. Causes of poor outcome after cataract surgery in Satkhira district, Bangladesh. Eye (Lond) 2008;22:1054 – 6. 29. Nirmalan PK, Thulasiraj RD, Maneksha V, et al. A population based eye survey of older adults in Tirunelveli district of south India: blindness, cataract surgery, and visual outcomes. Br J Ophthalmol 2002;86:505–12. 30. Murthy GV, Vashist P, John N, et al. Prevalence and visionrelated outcomes of cataract surgery in Gujarat, India. Ophthalmic Epidemiol 2009;16:400 –9. 31. National Survey on Blindness and Visual Outcomes after Cataract Surgery (2001-2002). New Delhi, India: National Program for Control of Blindness, Ministry of Health Family Welfare, Govt. of India; 2002: 88-92. Available at: http:// www.vision2020india.org/downloads/National_Survey_on_ Blindness_and_Visual_Outcomes_after_Cataract_Surgery_NPCB. pdf. Accessed August 7, 2010. 32. Eusebio C, Kuper H, Polack S, et al. Rapid assessment of avoidable blindness in Negros Island and Antique District, Philippines. Br J Ophthalmol 2007;91:1588 –92. 33. Bassett KL, Noertjojo K, Liu L, et al. Cataract surgical coverage and outcome in the Tibet Autonomous Region of China. Br J Ophthalmol 2005;89:5–9.
Footnotes and Financial Disclosures Originally received: April 1, 2010. Final revision: July 20, 2010. Accepted: August 11, 2010. Available online: November 4, 2010. 1
Financial Disclosure(s): The author(s) have no proprietary or commercial interest in any materials discussed in this article. Manuscript no. 2010-479.
Ministry of Health Minna, Niger State, Nigeria.
2
International Centre for Eye Health, London School of Hygiene and Tropical Medicine, London, United Kingdom.
3
Moorfields Eye Hospital, London, United Kingdom.
4
National Eye Centre Kaduna, Nigeria.
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This study was funded by CBM, Sightsavers International, and Velux Stiftung. Correspondence: Gudlavalleti V. S. Murthy, MD, MSc, International Centre for Eye Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT. E-mail: [email protected]. *The Nigeria National Blindness and Visual Impairment Study Group is available at http://aaojournal.org.