Systematic review of population-based studies of the prevalence of cataracts

Methodological quality of the review: Low confidence

Author: Acosta R, Hoffmeister L, Roman R, Comas M, Castilla M, Castells X.

Region: Europe, United states of America (USA) and Australia

Sector: Age-related cataract

Sub-sector: Prevalence; epidemiology; risk factors

Type of cataract: Age-related cataract

Equity focus: None specified

Review type: Other review

Quantitative synthesis method: Descriptive narrative of results

Qualitative synthesis methods: Not applicable

Background

Cataract is a chronic disease associated with the ageing process. The gradual increase of life expectancy has led to a substantial increase in the prevalence of cataracts, which affects a growing proportion of the population. It has a great impact in the older population and its influence on the utilization of health services and the waiting lists for cataracts surgery in many developed countries.

Research objectives

To analyse the existing evidence on the prevalence of cataract in healthy white adults over 40 years of age.

Main findings

The authors included ten studies in the review: three from Europe, five from the USA and two from Australia. These studies utilized three types of measurements: the ensuing visual acuity (VA) deficit, the opacification of the lens and a combination of both. Total prevalence figures varied considerably from 5% to 30%. In studies reporting only lens opacification, the prevalence ranged from 15-19%.When both measures were reported together the prevalence of cataract ranged from 15%-30%.

Authors found that the overall prevalence increased with age, reaching 40% and more than 60% in populations older than 70 and 75 years respectively. The prevalence among women was higher than that among men, with a more marked increase being evident at older ages than for men. They conclude that variations in criteria used within studies made it difficult to compare them, but overall it can be concluded that cataract increases with age and is more prevalent in women. They note that health systems need to account for this tendency when planning for services.

Authors suggested that future research should include estimated prevalence rates based on the degree of disability cataracts produced in patients. This is relevant since, in clinical practice, one of the predominant criteria for determining the need of surgical treatment is the functional limitation caused by cataract independent of VA or lens opacity morphology.

Methodology

Authors included population studies written only in English, Spanish, French or Italian, of healthy non-institutionalized adults over 40 and white race (similar to the population of Spain), with a minimum of 1,000 individuals, published between 1980 and 2002 and reported sample selection process.

PUBMED was searched for population studies on cataract prevalence. Authors also searched reference lists and literature reviews from the websites of the National Eye Institute, Alberta University and the NHS Center for Reviews and Dissemination, British Columbia and Department of Health UK. Authors conducted a narrative analysis of the results, which seemed appropriate.

Applicability/external validity

No methods were used either to assess the applicability /external validity of the results or to discuss how generalizable the results are.

Geographic focus

As no cataract prevalence studies were found for the Spanish population, authors included studies conducted in countries consisting of populations with similar characteristics with that of Spain. Therefore, findings from this review may not be applicable to middle- and low-income countries.

Quality assessment

Authors conducted a narrative synthesis of the findings, which seemed appropriate due to the vast differences of included studies such as the difference in study population. Authors appropriately reported inclusion/exclusion criteria used for study selection. However, this review had some important limitations.  The authors did not avoid publication and language bias in the search, only one relevant database was searched and only articles written in English, Spanish, Italian and French were included in the review.  Authors did not report methods used to select studies and to extract data of included studies, nor did they discuss the quality and risk of bias of included studies. Therefore, there is low confidence in the conclusions about the effects of this study.