Elimination of avoidable blindness due to cataract: Where do we prioritize and how should we monitor this decade?

Methodological quality of the review: Low confidence

Author: Murthy GV, John N, Shamanna BR, Pant HB.

Region: Low- to middle-income countries/regions

Sector: Cataract, avoidable blindness, prevalence, cataract surgical rate

Sub-sector: None

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative synthesis

Qualitative synthesis methods: Not applicable

Background

Cataract causes more than half of all blindness in a number of low- to middle-income countries (LMIC) and cataract blindness remains a global burden to date. The ‘ageing’ of populations in LMIC indicates that more people will be at risk of age related eye problems including cataract in years to come. There is a need keep pace with this increase in cataract prevalence in order to achieve the goals set out in Vision 2020 and the goal of eliminating avoidable blindness. Only by tackling the magnitude and effectively monitoring cataract blindness can these goals be realistically achieved.

Research objectives

To Review existing situation and assess what monitoring indicators may be useful to chart progress towards attaining the goals of Vision 2020.

Main findings

The authors included population-based studies from low- and middle-income countries. However, it is not clear how many studies were included in total. Studies evaluated the prevalence and causes of blindness, cataract surgical coverage and surgical outcomes.

The prevalence of blindness, based on presenting vision ranged from 0.4% to 8.1% whilst most studies (number not cited)  reported a ration of visual impairment to blindness of 3:1 to 4:1 (with the exception of one study in Nepal reported visual impairment to be eight times higher). The proportion of blindness due to cataract ranged from 36% to 89% in most studies (number not cited) except Cameroon where it was 21%.

To illustrate the relationship between cataract blindness and country level development, some data (not specified) from the included studies was plotted against Human Development Index rankings. Worse HDI ranks were associated with higher prevalence of cataract blindness.

11 studies reported the population prevalence of cataract surgery, which ranged from 1.6% in Nigeria and Malawi to 17.6% in India. Seven of the 20 studies that reported on cataract surgical coverage showed that less than half of those who potentially needed surgery were operated, implying that more than half of the population did not receive the required surgery.

18 surveys reported on visual outcomes after cataract surgery at population level. A good visual outcome after surgery was positively correlated with higher cataract surgical coverage using a 20/400 cut-off. Cataract surgical rate was positively correlated with cataract surgical coverage.

Authors noted that any cataract initiative needs to emphasize cataract surgical programmes to fill the ongoing need and translate developments in cataract technology into a real benefit for blind and visually impaired people from poorer development settings. It suggested that future research should also investigate the barriers that prevent the uptake of cataract surgery and encourage better uptake of these services. Indication that good visual outcomes ‘fuel’ cataract surgical coverage means that there is value in monitoring cataract surgeries and ‘providing timely feedback to surgeons’ on the quality of surgical outcomes.

Methodology

The authors included population based studies from LMICs which evaluated the prevalence and causes of blindness, cataract surgical coverage and surgical outcomes. Details of the search strategy to identify relevant studies to be included in the review were not reported.

A narrative approach was used to present results from the included studies. The prevalence of blindness or visual impairment was calculated by the authors as this data was not specifically reported in the included studies. This was calculated by taking the proportion of blind/visually impaired and multiplying by the total number examined. Then the number of cataract-blind or visually impaired was divided by the total number examined in the survey.

On working with HDI data, sets of data from comparative population groups was extracted from the included surveys and plotted against the HDI ranking system. This was conducted with five studies from South America, six studies from Africa and four from Asia.

Applicability/external validity

The review did not specifically focus in how generalizable the results are, although it is noted that one of the weaknesses of the methodology is that data is largely taken from the national level while the included studies were not nationally representative. Therefore, results from the methodology might not have represented a population as a whole accurately. Most included studies are difficult to compare due to variation in methodology, age groups and definitions between them and data should be used only to infer possible trends in LMICs.

Geographic focus

Results from the review only included population-based studies from low- to middle-income countries in Asia, Africa and South America. The results may have shed light on some of the trends in low- to middle-income countries although authors did recognize that heterogeneity between studies made solid comparisons challenging.

Quality assessment

Low confidence was attributed in the conclusions about the effects of this study as major limitations were identified. Searched databases, search restrictions and methods used to select studies, extract data, and quality assess the studies were not reported.

One of the weaknesses of the methodology was that data was largely taken from the national level while the included studies were not nationally representative. Therefore, results from the methodology might not have represented a population as a whole accurately. Most included studies were difficult to compare due to variation in methodology, age groups and definitions between them and authors recognize that data should be used only to infer possible trends in low- and middle-income countries and not come to concrete conclusions.