Abstract
Background:
The Nigeria national blindness survey has documented region-specific prevalence and causes of visual impairment in the country. However, there is need for local studies to ascertain specific causes of visual impairment peculiar to each community, as this varies from one locality to another.
Aim:
To determine the causes of blindness and low vision among patients presenting to the Eye Clinic, Federal Medical Center Abeokuta, Nigeria
Study design:
A retrospective study.
Materials and Methods:
Medical records of all patients seen at the Eye Clinic, Federal Medical Center, Abeokuta, Nigeria between January 2011 and December 2012 were reviewed.
Results:
Out of the 5,352 patients managed during the period, 474 (8.9%) were blind, 3,178 (59.4%) had low vision while 1,700 (31.7%) had “normal vision”. The risk of visual impairment increased with age. The major causes of blindness were cataract (32.5%), glaucoma (20%) and age-related macular degeneration (12.8%), while the most common causes of low vision were uncorrected refractive errors (20.5%), cataract (17.6%) and glaucoma (14.8%).
Conclusion:
Cataract, glaucoma and uncorrected refractive errors are the leading causes of visual impairment in Abeokuta, Nigeria. Public enlightenment coupled with prompt and effective management will reduce the burden of blindness in the country.
Keywords: Blindness, Etiology , Low vision, Nigeria, Visual impairment
Introduction
Introduction
The World Health Organization (WHO) categorized visual impairment into low vision and blindness. Blindness is defined as presenting visual acuity of less than 3/60 in the better eye of an individual or visual field less than 100 from fixation while low vision (sub-classified as mild, moderate or severe visual impairment) is defined as visual acuity of less than 6/12 to 3/601. Globally, about 39 million people are estimated to be blind, and 246 million with low vision, making up 285 million people with different levels of visual impairment2.
Asia and Africa bear about 75% of the global burden of blindness of which about 80% are avoidable2. The prevalence of blindness from the Nigerian National blindness and visual impairment survey3 was 4.2% but this varied between the six geo-political zones in the country. The south-west zone has the lowest prevalence of 2.8% and north-east has the highest rate of 6.1%3. Many factors contribute to the differences in the etiology and distribution of visual impairment across communities and within geographical locations4 with older individuals and the less privileged individuals in the community being at higher risk3. Local studies are therefore necessary to strengthen National surveys in determining the etiology and distribution of visual impairment in specific localities. Hence, this study was carried out to determine the causes of visual impairment among patients presenting to the Eye Clinic of Federal Medical Center (FMC), Abeokuta, Nigeria. This will help in planning blindness-prevention programs for the inhabitants of the state and its environs.
Materials and Methods
Medical records of all patients seen in the Eye Clinic of Federal Medical Center, Abeokuta, Nigeria between January 2011 and December 2012 were retrieved and data collected included the demographics, presenting visual acuity, examination findings and diagnoses. Federal Medical Center Abeokuta is a tertiary health institution located in the south-west Nigeria. It has a well established Ophthalmology Department offering out-patient, in-patient, surgical and other services to citizens of the city and surrounding towns and villages. There are three consultant ophthalmologists, three resident doctors, one optometrist and four trained ophthalmic nursing staff in the clinic. Patients presenting to the Eye Clinic undergo preliminary visual acuity assessment by the trained ophthalmic nurses. Refraction is carried out by the optometrist and the ophthalmologists who also reviewed all refraction carried out by the optometrist before making the diagnoses. Detailed examination of all patients and diagnoses are made by the ophthalmologists and appropriate management instituted. Detailed eye examination include cross-checking the visual acuity, anterior segment examination with pen touch and slit-lamp machine, intra-ocular pressure by applanation, and dilated fundoscopy with binocular indirect ophthalmoscope. Slit lamp examination with 78D lens is carried out in patients with suspected posterior segment pathology and those suspected of glaucoma undergo gonioscopy and visual fields analysis. The operational definitions of visual impairment used in this study are as defined by WHO1 and also used in the Nigerian national blindness survey study protocol5. Where two or more disorders coexist in a patient, the most significant cause of visual impairment was recorded for this study, or the one that is most amenable to treatment and hence, prevention where more than one significant cause is documented5. The diagnosis of cataract was made when visually significant lens opacity was the most significant cause of visual impairment identified in the patient while that of glaucoma was based on glaucomatous optic atrophy (cup/disc ratio of ≥0.5) with characteristic visual field defects. The study conforms to the ethics of Helsinki Declaration.
Reports
Statistical analysis
All data were analyzed using the Epi-Info version 6 statistical package to generate frequency distribution of all variables. Data were summarized in simple percentages. Data have been presented in simple tabular form
Results
A total of 5,352 patients (aged 1 month to 103 years, male to female ratio of 1.1:1) were managed during the study period with 1,700 (31.7%) of them having “normal vision”. Of the 3,652 (68.2%) patients who were visually impaired, 474 (8.9%) were blind and 3,178 (59.4%) had low vision as shown in Table 1. There was an increased risk of visual impairment with age as more patients aged ≥ 60 years (14.1% blind and 59.4% with low vision) were visually impaired compared with those less than 40 years (1.8% blind, 58% with low vision) as in Table 2. Most of the patients with low vision had mild (22.7%) or moderate (24.6%) visual impairment as shown in Table 3.
The major causes of blindness in this study were cataract (32.5%), glaucoma (20%) and age-related macular degeneration (12.8%) as shown in Table 4, while the most common causes of low vision were uncorrected refractive errors (20.5%), cataract (17.6%) and glaucoma (14.8%) as shown in Table 5.
Discussion
Globally, the number of blind and visually disabled persons is on the increase, and this has been attributed in part to population increase and ageing6. The prevalence of blindness of 8.9% in this study is similar to previous hospital-based studies7,8 in the country but higher than prevalence from community-based studies4,9,10,11,12. This can be attributed to the study design and selection bias in hospital-based studies. However, Rabiu13 reported a prevalence of 8.2% in a community-based survey of a remote, underserved, rural northern Nigerian community.
Risk of visual impairment increased with age, in line with reports from previous studies7,10,11,14,15 , as many visually disabling diseases occur in the elderly. With increasing longevity following improvement in health care delivery systems, this burden of blindness is likely to increase.
The leading cause of blindness in this study is cataract, similar to previous reports4,7,8,11,14,15,16,17 from developing countries. Cataract had remained the leading cause of blindness in Nigeria and other developing countries, and, the increasing adult population with inadequate and inefficient control programs had contributed to the great backlog13. The cataract surgical coverage for most developing countries had remained poor13, hence, greater efforts at increasing the quantity and quality of cataract surgeries should be put in place to address this.
Glaucoma is the second most common cause of blindness and third leading cause of low vision in the population studied, as previously reported7,8,10,11,15 in the country. This is of great concern as glaucoma causes irreversible blindness and glaucoma patients in this region often present late to hospitals with bilateral blindness18.
The leading cause of low vision is uncorrected refractive errors, seen in about one fifth of the patients, closely followed by cataract. This agrees with previous studies19,20 and WHO estimate of causes of global visual impairment2. The presence of two tertiary institutions and several secondary schools in the cosmopolitan city of Abeokuta could also account for the high proportion of those with mild and moderate visual impairment from uncorrected refractive errors presenting to the Eye Clinic.
It is interesting to note an increasing proportion of blindness and low vision caused by retinal diseases in this study. This has been attributed in part, to change in lifestyle of individuals in developing countries, leading to increasing prevalence of diabetic retinopathy; an increasing adult population causing age-related macular degeneration, and reduction in infective causes of blindness2,21,22.
A major limitation of this study, similar to other hospital-based studies, is selection bias, as more patients with blindness are likely to be seen in the hospital setting, and thus, may not reflect a true community-based prevalence. Also, due to the retrospective design, all examinations were not carried out by a single ophthalmologist. However, it has highlighted the major causes of blindness and low vision among those with eye problems in this community and, possible conditions to be targeted in blindness prevention and control programs. A properly conducted population-based study will address some of the limitations in this study.
Conclusions
In conclusion, the leading causes of blindness (cataract and glaucoma) and low vision (uncorrected refractive errors and cataract) in this study are avoidable, similar to previous reports3,4,7,8,10,11,14,15,17 . Greater effort at providing good cataract surgical services, glaucoma screening and optical services with increased public enlightenment on these diseases is advocated.
Table 1: Age categories and visual status of 5,352 patients
| Age groups (years) | Frequency | Normal vision (%) | Visual impairment | |
| Blind (%) | Low vision (%) | |||
| ≤10 | 329 | 156 (47.4) | 5 (1.5) | 168 (51.1) |
| 11-20 | 387 | 180 (46.5) | 7 (1.8) | 200 (51.7) |
| 21-30 | 493 | 182 (36.9) | 10 (2.0) | 301(61.1) |
| 31-40 | 558 | 193 (34.6) | 10(1.8) | 355 (63.6) |
| 41-50 | 642 | 197 (30.7) | 58 (9.0) | 387 (60.3) |
| 51-60 | 728 | 205 (28.2) | 72 (9.8) | 451 (62.0) |
| 61-70 | 792 | 202 (25.5) | 93(11.7) | 497 (62.8) |
| 71-79 | 714 | 192 (26.9) | 81(11.3) | 441 (61.8) |
| >80 | 709 | 193 (27.2) | 138 (19.5) | 378 (53.3) |
| Total | 5,352 | 1700 (31.7) | 474 (8.9) | 3,178 (59.4) |
Table 2: Increased risk of visual impairment with age in 5,352 patients
| Age groups (years) | Frequency | Normal vision (%) | Visual impairment (%) | |
| Blind (%) | Low vision (%) | |||
| < 40 | 1767 | 711 (40.2) | 32 (1.8) | 1,024 (58.0) |
| 40-60 | 1370 | 402 (29.3) | 130 (9.5) | 838 (61.2) |
| ≥ 60 | 2215 | 587 (26.5) | 312 (14.1) | 1316 (59.4) |
| Total | 5,352 | 1,700 (31.7) | 474 (8.9) | 3,178 (59.4) |
Table 3: Visual acuity of 5,352 patients seen in the Eye clinic
| Visual acuity | Category | Frequency | Percent |
| 6/4-6/12 | Normal or Near normal | 1,700 | 31.7 |
| <6/12-6/18 | Mild Visual Impairment | 1,219 | 22.7 |
| <6/18-6/60 | Moderate Visual Impairment | 1,314 | 24.6 |
| <6/60-3/60 | Severe Visual Impairment | 645 | 12.1 |
| <3/60-NPL | Blind | 474 | 8.9 |
| Total | 5,352 | 100 | |
Table 4: Causes of blindness in 474 patients
| Disease | Frequency | Percent |
| Cataract | 154 | 32.5 |
| Glaucoma | 95 | 20.0 |
| Age-related macular degeneration | 58 | 12.8 |
| Corneal diseases | 43 | 9.1 |
| Diabetic retinopathy | 41 | 8.5 |
| Uncorrected refractive errors | 37 | 7.8 |
| Hypertensive retinopathy | 22 | 4.5 |
| Non-glaucomatous optic atrophy | 22 | 4.5 |
| Endophthalmitis | 2 | 0.4 |
| Total | 474 | 100 |
Table 5: Causes of low vision in 3,178 patients
| Disease | Frequency | Percent |
| Uncorrected refractive errors | 650 | 20.5 |
| Cataract | 560 | 17.6 |
| Glaucoma | 472 | 14.8 |
| Diabetic retinopathy | 359 | 11.2 |
| Age-related macular degeneration | 310 | 9.8 |
| Hypertensive retinopathy | 285 | 9.0 |
| Corneal diseases | 270 | 8.5 |
| Pterygium | 200 | 6.3 |
| Non-glaucomatous optic atrophy | 67 | 2.1 |
| Sickle cell retinopathy | 5 | 0.2 |
| Total | 3,178 | 100 |
Footnotes
Competing Interests: The authors have declared that no competing interests exist.
Grant support: None
References
- 1.Organization World Health. Organization., World Health; ICD update and revision platform: change the definition of blindness. [Google Scholar]
- 2.Pascolini D, Mariotti SPM. Global estimates of visual impairment: 2010. Br J Ophthalmol. 2012;96(5):614–618. doi: 10.1136/bjophthalmol-2011-300539. [DOI] [PubMed] [Google Scholar]
- 3.Abdull MM, Sivasubramaniam S, Murthy GVS, Gilbert CE, Abubakar T, Ezelum C. Causes of Blindness and Visual Impairment in Nigeria: The Nigeria National Blindness and Visual Impairment Survey. Invest Ophthalmol Vis Sci. 2009;50(9):4114–4120. doi: 10.1167/iovs.09-3507. [DOI] [PubMed] [Google Scholar]
- 4.Adeoti CO. Prevalence and causes of blindness in a tropical African population. West Afr J Med. 2004;23(3):249–252. doi: 10.4314/wajm.v23i3.28132. [DOI] [PubMed] [Google Scholar]
- 5.Dineen B, Gilbert CE, Rabiu MM, Kyari F, Abdull MM, Abubakar T. The Nigerian national blindness and visual impairment survey: Rationale, objectives and detailed methodology. BMC Ophthalmol. 2008;8:17. doi: 10.1186/1471-2415-8-17. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Thylefors B. A global initiative for the elimination of avoidable blindness. Community Eye Health. 1998;11(25):1–3. [PMC free article] [PubMed] [Google Scholar]
- 7.AE Omoti. Aetiology of blindness in Benin City, Nigeria. Ann Afr Med. 2004;3(2):87–89. [Google Scholar]
- 8.Nwosu SNN. Blindness and visual impairment in Anambra State, Nigeria. Trop Geogr Med. 1994;46(6):346–349. [PubMed] [Google Scholar]
- 9.Abiose A, Murdoch I, Babalola O, Kaduna Collaboration for Research on Onchocerciasis. Distribution and etilogy of blindness and visual impairment in mesoendemic onchocercal commnities, Kaduna State, Nigeria. Br J Ophthalmol. 1994;78:8–13. doi: 10.1136/bjo.78.1.8. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Ajibode HA. The prevalence of blindness and visual impairment in Ikenne Local Government Area of Ogun State, Nigeria. Nig J Ophthalmol. 1999;7(1):23–27. [Google Scholar]
- 11.Onakpoya OH, Adeoye AO, Akinsola FB, Adegbehingbe BO. Prevalence of blindness and visual impairment in AtakunmosaWest Local Governmant Area of southwestern Nigeria. Tanzania Health Res Bull. 2007;9(2):126–131. doi: 10.4314/thrb.v9i2.14315. [DOI] [PubMed] [Google Scholar]
- 12.Faal H, Minassian D, Sowa S, Foster A. National survery of blindness and low vision in The Gambia: Results. Br J Ophthalmol. 1989;73:82–87. doi: 10.1136/bjo.73.2.82. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Rabiu MM. Cataract blindness and barriers to uptake of cataract surgery in a rural community of nothern Nigeria. Br J Ophthalmol. 2001;85(776):780. doi: 10.1136/bjo.85.7.776. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 14.Oluleye TS, Ajaiyeoba AI, Akinwale MO, Olusanya BA. Causes of blindness in southwestern Nigeria: a general hospital clinic study. Eur J Ophthalmol. 2006;16(4):604–607. doi: 10.1177/112067210601600416. [DOI] [PubMed] [Google Scholar]
- 15.Ezepue UF. Magnitude and causes of blindness and low vision in Anambara State of Nigeria (results of 1992 point prevalence survey) Public Health. 1997;111(5):305–309. [PubMed] [Google Scholar]
- 16.Dulal S, Sapkota YD. Prevalence of blindness and visual impairment and its causes among people aged 50 years and above in Karnali Zone, Nepal. Nepal J Ophthalmol. 2012;4(8):282–287. doi: 10.3126/nepjoph.v4i2.6545. [DOI] [PubMed] [Google Scholar]
- 17.Adegbehingbe BO, Fajemilehin BR, Ojofeitimi EO, Bisiriyu LA. Blindness and visual impairment among the elderly in Ife-Ijesha zone of Osun State, Nigeria. Indian J Ophthalmol. 2006;54:59–62. doi: 10.4103/0301-4738.21620. [DOI] [PubMed] [Google Scholar]
- 18.Enoch ME, Omoti AE, Momoh RO. Glaucoma in a suburban tertiary care hospital in Nigeria. J Ophthalmic Vis Res. 2010;5(2):87–91. [PMC free article] [PubMed] [Google Scholar]
- 19.Oladigbolu KK, Abah ER, Chinda D, Anyebe EE. Pattern of eye diseases in a university health service clinic in northern Nigeria. Niger J Med. 2012;21(334):337. [PubMed] [Google Scholar]
- 20.Bagaiya T, Pam V. Refractive errors in Kaduna, Nigeria. Niger J Med. 2003;5:106–109. [Google Scholar]
- 21.Oluleye TS, Ajaiyeoba AI. Retinal diseases in Ibadan. Eye. 20(12):1461–1463. doi: 10.1038/sj.eye.6702343. [DOI] [PubMed] [Google Scholar]
- 22.Nwosu SNN. Prevalence and pattern of retinal diseases at the Guinness Eye Hospital, Onitsha, Nigeria. Ophthalmic Epidemiol. 2000;7(1):41–48. [PubMed] [Google Scholar]