ORIGINAL STUDY Rapid assessment of avoidable blindness in Masvingo Province, Zimbabwe: considerations for resource-limited settings

Rapid assessment of avoidable blindness in Masvingo Province, Zimbabwe: considerations for resource-limited settings

D Minnies, NDMT Clin Path, NHDMT, MPH, PhD (Public Health); Director: Community Eye Health Institute, Division of Ophthalmology, University of Cape Town, South Africa ORCID: https://orcid.org/0000-0002-9173-782X

B Macheka, MBChB, MMed(Ophth); Lead Government Ophthalmologist, Ministry of Health and Child Care, Zimbabwe

J Joseph, MBChB, MMed(Ophth), Provincial Ophthalmologist, Masvingo Province, Ministry of Health, Zimbabwe

C Cook, MBChB, DO, MPH, FRCOphth SA; Emeritus Professor, Division of Ophthalmology, University of Cape Town, South Africa ORCID: https://orcid.org/0000-0001-5661-7390

Corresponding author: Dr Deon Minnies, H53 Old Main Building, Groote Schuur Hospital, Observatory 7925, South Africa; tel: +27 21406 6039; email: d.minnies@uct.ac.za

Abstract

Background: A rapid assessment of avoidable blindness was conducted to assess the situation of blindness and visual impairment in Masvingo Province, Zimbabwe, using the standard rapid assessment of avoidable blindness (RAAB) methodology.

Methods: A sample size of 3 756 was calculated by RAAB software, using an estimated prevalence of blindness of 3.0%±0.7% with 95% confidence interval based on previous RAAB findings in the region. The sampling was done using multistage systematic cluster random sampling, with 76 clusters of 50 people aged 50 years or above selected with probability proportional to size (PPS). A total of 3 795 people were examined, representing a response rate of 99.9%. Examination procedures included measurement of visual acuity (VA) with available correction and pinhole correction, assessment of lens status and examination of the fundus with a direct ophthalmoscope. Data was collected using the RAAB smartphone application.

Results: The sample prevalence of bilateral blindness with available correction (presenting VA <3/60) in the better eye was 3.6% (95% confidence interval: 2.9–4.2). Untreated cataract (65.2%) was the most common cause of blindness followed by glaucoma (16.3%) and non-trachomatous corneal opacity (10.4%).

Just over half (52.2%) of people blind due to cataract (presenting VA <3/60) had undergone surgery. Of the eyes operated for cataract, 59.7% could see 6/18 or better (‘Good outcome’) while 25.7% could not see 6/60 (‘Poor outcome’) with available correction.

Conclusion: There is a need to further strengthen the capacity of the Masvingo provincial eye care programme through effective planning, monitoring and management of eye care services to meet high performance targets, nationally and globally.

Keywords: rapid assessment of avoidable blindness, blindness, visual impairment, Zimbabwe

Funding: The source of the funding is from a grant from Christian Blind Mission (CBM), as part of a project being implemented by Zimbabwe Council for the Blind.

Conflict of interest: The authors declare they have no conflicts of interest with regard to this study.

Introduction

The Vision Loss Expert Group reported that, in 2015, the prevalence of blindness was 36 million globally,1 and that a further 216.6 million people were moderately to severely visual impaired, making a total of 253 million people with vision loss.2 The World Health Organization (WHO) defines blindness as ‘presenting visual acuity worse than 3/60’; severe visual impairment as ‘presenting visual acuity worse than 6/60 but better than 3/60’; moderate visual impairment as ‘presenting visual acuity worse than 6/18 but better than 6/60’ and functional low vision as incurable presenting visual acuity worse than 6/18 but with light perception, all in the better eye.3

Almost 90% of people affected by blindness or visual impairment live in low- and middle-income countries, and more than 75% of visual impairment is avoidable.4 About half of the 47 countries in sub-Saharan Africa whose data contributed to the Vision Atlas had population surveys done, and 36% of countries had a national blindness prevention committee/national eye care strategy in place.4

Rapid assessment of avoidable blindness (RAAB) surveys are widely used to determine the burden of blindness and visual impairment for the purpose of planning and advocacy for eye care services.5 The RAAB is a complete system, ready to be used by local eye care teams, and includes provision for training, data collection and analysis.6 The 11 RAAB surveys conducted in the southern region of sub-Saharan Africa between 2009 and 2017 show that the blindness prevalence in people aged 50 years or above ranged from 1.3–7.1%, with a median of 3.3%.4 Cataract surgical coverage ranged from 10–96% (median 49%) in operated eyes in sample with best correction. Posterior segment disease caused a median of 24.6% (range 15.9–67.6%) of blindness.

According to the National Census of 2012, Masvingo Province, Zimbabwe, had a population of 1.5 million people,7 with 11.9% of the population aged 50 years or above. Eye care services are provided through tertiary, secondary and primary levels of care amid severe shortages of equipment, consumables and eye health specialists nationally.8 Even so, in 2016, a total of 14 898 eye care outpatient consultations, 2 499 refractions and 1 612 cataract operations were performed.9 The cataract surgical rate of over 1 000 per million is double the national average of approximately 500 per million.10

A RAAB was conducted in Masvingo Province to obtain baseline information as part of a national strategy to improve eye care services in rural provinces. The aim was to determine the magnitude and causes of avoidable blindness and visual impairment in people aged 50 years and above. Additionally, the cataract surgical coverage, the outcomes of cataract surgery and the barriers to uptake of cataract surgery were determined.

Methods

This was a population-based crosssectional study.

A sample size adequate to demonstrate a prevalence of blindness of 3.0% ± 0.7% with 95% confidence was calculated by the RAAB software, using the standard formula for finite populations:

Sample size = Z*Z(P(1-P))/D*D, where Z = percentile of the standard normal distribution, P = expected prevalence of the condition and D = half the width of the desired sample confidence interval

This was adjusted for non-participation (10%) and design effect (1.5) due to clustering, resulting in a sample size of 3 756. A sampling frame was created and consisted of 261 enumeration areas, called wards in Masvingo Province. Sampling was done using multi-stage systematic cluster random sampling. Using the cluster selection module in the RAAB software, 76 clusters of 50 people aged 50 years or above (i.e. a total of 3 800 people) were selected with probability proportional to size, followed by random selection of participants within the sampled clusters.

Five examination teams, four of which comprised ophthalmic nurses and the other comprising two ophthalmologists, completed a five-day training programme led by a certified RAAB trainer. The ophthalmologist team was assigned the ‘gold standard’ role for the interobserver variation (IOV) test. The IOV test is a means of achieving validity of the field data. The aim is to achieve high interobserver agreement (kappa coefficient values of 0.7–0.8 or higher for each of the teams) when performing the examination procedures.

The training covered the key knowledge and skills aspects required for collecting data for analysis to produce the RAAB results. This included standardised selection, enrolment and procedures to examine participants, as well as coding of major causes of vision loss in each eye and the person examined.

Additionally, the examination teams were trained in the use of the RAAB software as well as the posting of the records to the database for analysis. Standardised meanings for ‘place’ and ‘cost of surgery’ were also defined during the training. Four cluster informers and a survey coordinator received training in aspects of sampling, monitoring and data administration.

Data was collected using the RAAB software on smartphones. Minimal demographic information was captured for the purpose of identification, analysis and referral to an eye clinic, if indicated. Interviews were conducted in the respondents’ homes in the local language.

Examination procedures included measurement of visual acuity (VA) with available correction (i.e. their own spectacles) and pinhole correction, assessment of lens status in each eye with distant direct ophthalmoscopy and fundoscopy with a direct ophthalmoscope through a dilated pupil if VA<6/18 and not due to cataract, corneal scar or refractive error.

Using the RAAB software for analysis, the following indicators were determined from the data collected: the prevalence of blindness, severe visual impairment (SVI) and moderate visual impairment (MVI); the prevalence of avoidable blindness, SVI and MVI; the prevalence of blindness, SVI and MVI from cataract, the main causes of blindness, SVI and MVI; the prevalence of aphakia and/or pseudophakia; the cataract surgical coverage, i.e. the proportion of people needing surgery who actually had surgery; the visual outcome of cataract surgery; barriers to cataract surgery; prevalence of uncorrected refractive errors and uncorrected presbyopia; and various cataract surgery service indicators (age at time of surgery, place, costs and type of surgery, cause of visual impairment after cataract surgery).

All indicators were subdivided by sex and age group. The WHO definitions of blindness and visual impairment were used. Avoidable causes of blindness and visual impairment were grouped under treatable (e.g. cataract, refractive error and uncorrected aphakia), or preventable (e.g. surgical complications, corneal opacity, diabetic retinopathy and glaucoma).

Results

Of the 3 800 people aged 50 years or above who were eligible, 3 795 people were examined, representing a response rate of 99.9% (Table I). The sample comprised 1 533 males and 2 262 females, 40.4% and 59.6% of the sample, respectively.

The sample prevalence of bilateral blindness with available correction (presenting visual acuity or PVA <3/60) in people aged 50 years or above in the better eye was 3.6% (95% confidence interval: 2.9–4.2); 3.5% in males and 3.6% in females. The prevalence ratios of severe and moderate visual impairment are shown in Table II.

Extrapolating to the Masvingo Province, an estimated 6 684 people aged 50 years or above were bilaterally blind, an age and sex-adjusted prevalence of 3.9% (3.2–4.5). A further 4 362 people aged 50 years or above were severely visually impaired (SVI) and another 12 964 people had moderate visual impairment (MVI). Among them, 3 508 people aged 50 years or above had functional low vision (FLV), requiring low vision services.

Untreated cataract was the most common cause of bilateral blindness at 65.2%, followed by glaucoma (16.3%) and non-trachomatous corneal opacity (10.4%) (Table III). Untreated cataract (74.1%) was also the main cause of bilateral SVI, followed by glaucoma (8.2%) and uncorrected refractive error (5.9%). Uncorrected refractive error (21.5%) was the second most common cause (after untreated cataract, 69.7%) of bilateral MVI.

A total of 94.8% of bilateral blindness in persons was considered avoidable, 65.2% treatable, 11.1% preventable by primary eye care and 18.5% preventable by specialised ophthalmic services (Figure 1). A total of 5.2% was considered not avoidable and required rehabilitation/low vision services. Posterior segment diseases accounted for 22.2% of bilateral blindness.

Figure 1: Blindness, SVI and MVI in persons by intervention category

In Masvingo Province, 52.2% of people who were blind due to cataract (VA<3/60) had been operated on: 50.0% of males and 52.8% of females. The coverage for people with VA<6/60 was 40.8% (males 37.0% and females 42.2%) and for people with VA<6/18 was 26.5% (22.8% males and 28.5% females).

Of the 191 eyes operated for cataract, 114 (59.7%) could see 6/18 or better (‘Good outcome’) and 25.7% could not see 6/60 (‘Poor outcome’) with available correction (Table IV). Overall, 67.3% of poor outcomes were caused by sequelae to cataract surgery with poor selection (18.4%) and surgical technique (14.2%) the second and third most common causes of poor visual outcomes respectively.

‘Cost’ (48.2%), ‘Need not felt’ (18.3%) and ‘Cannot access treatment’ (18.3%) were the main reasons participants who were blind due to untreated cataract did not go for surgery. Females were more likely to report ‘cost’ (56.8%) compared to males (30.2%) (Figure 2).

Figure 2. Barriers to cataract surgery in sample (bilateral BCVA<6/60 due to cataract)

The prevalence of total refractive errors also higher than the median prevalence was 4.6% (males 4.8% and females 4.4%) of blindness of the most recent 11 RAAB with 1.6% prevalence for uncorrected surveys (3.3%) conducted in the southern refractive error, equally occurring in sub-Saharan African region.4 males and females. The prevalence of Although the cataract surgical coverage uncorrected presbyopia was high (93.0%) in Masvingo is higher than both the (Table V). Manicaland and the sub-regional median,

Glaucoma was the most common it still means that cataract blindness is posterior segment cause of blindness in inadequately controlled. The age- and persons (16.3%) and eyes (10.4%). Diabetic sex-adjusted results show that there were retinopathy caused blindness in 0.7% and 3 628 cataract-blind people, more than 0.5% eyes and people respectively. double the number of cataract surgeries

The age- and sex-adjusted prevalence performed in a year. Careful selection of functional low vision, not caused by of bilaterally blind people should be a cataract, refractive error, uncorrected priority to reduce the number of cataractaphakia or pseudophakia with posterior blind people in the province. capsular opacity) and requiring low vision Visual outcomes after cataract surgery services was 1.8% (1.4–2.3).

Discussion

There was a higher sample and age- and sex-adjusted prevalence of blindness in Masvingo Province when compared to the Manicaland RAAB findings in 2016, when a sample and age- and sex-adjusted prevalence of blindness in people aged 50 years and above of 3.7% and 3.1% respectively was reported.11 This was also higher than the median prevalence of blindness of the most recent 11 RAAB surveys (3.3%) conducted in the southern sub-Saharan African region.4

Although the cataract surgical coverage in Masvingo is higher than both the Manicaland and the sub-regional median, it still means that cataract blindness is inadequately controlled. The age- and sex-adjusted results show that there were 3 628 cataract-blind people, more than double the number of cataract surgeries performed in a year. Careful selection of bilaterally blind people should be a priority to reduce the number of cataract-blind people in the province.

Visual outcomes after cataract surgery are below the recommended standards of the WHO,8 mainly because of sequelae of surgery, suggesting that review of procedures, closer monitoring and improved case-finding and follow-up are necessary for improvement.

Glaucoma is the main posterior segment cause of blindness and low vision; therefore, further investments should be made to improve this aspect of ophthalmic services in the province.

Further considerations

Low-resource settings like Zimbabwe face particular challenges which can present limitations to the conduct of research or the interpretation of the findings. One of these is the low availability of ophthalmic medical staff for the conduct of RAABs, which creates a dependency on non-physician ophthalmic staff to do examinations and diagnosis independently of ophthalmologists in the field. This may affect diagnostic accuracy, especially for conditions in the posterior segment disease group, which may be more difficult to diagnose. The clinical monitoring and support provided by the ophthalmologists during the data collection period has been crucial to help overcome these challenges and needs to be further explored.

Another challenge is the differences in service uptake, quality and accessibility between sexes and across age groups, mostly because of socioeconomic reasons. In the Masvingo RAAB, the age and sex distribution of the sample mirrors that of the population in the survey area (female ratio in sample 0.596, female ratio in population 0.603). However, ‘Cost’ is a greater barrier to access of cataract surgery for women, compared to men. The possible extension to general health service uptake and participation in research needs to be carefully considered.

A further concern is the high response rate (of almost 100%), because it may suggest low autonomy on the part of the participant, due to fear or ignorance. It may also be because of incorrect enumeration practices, which could be the source of selection bias and therefore adversely affect the findings. This practice should be thoroughly addressed during training and in-field monitoring.

As cataract surgery is still the main strategy to reduce avoidable blindness, there is a need to further strengthen the capacity of the Masvingo provincial eye care programme. This may involve human resource development to improve the quality and the quantity of cataract operations. Making cataract surgery more affordable, perhaps by reducing the patient fees, providing subsidies and transport to increase access, could return favourable outcomes.

According to the WHO, the challenges of low cataract surgical coverage, low cataract surgical quality, and high user cost of services need to be addressed through effective planning, monitoring and management of eye care services to meet high performance targets, nationally and globally.12 These findings of the RAAB survey in Masvingo Province should help to build a strategy for investments in overall eye care programme development in the province and in the country.

Acknowledgements

This population-based survey was organised by the Ministry of Health and Child Care, in collaboration with CBM, Zimbabwe Council for the Blind and the Community Eye Health Institute, University of Cape Town. The research was funded through Standard Chartered Bank, Seeing is Believing project. Dr Susan Lewallen reviewed the draft and gave valuable input for improvement.

References

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12. World Health Organization. 2013. Universal eye health: a global action plan 2014–2019. 