The design, analysis, and interpretation of studies using measures of quality of life vary according to the context of use. In this paper we are primarily concerned with quality of life measures in clinical trials but our comments are relevant in other contexts. DesignApart from the usual considerations of good study design, particular issues in studies measuring quality of life are the choice of dimensions and the selection of instruments to measure these dimensions. There are also several practical considerations.

Background/aims: Exposure to systemic corticosteroid use is known to be associated with a risk of cataract. Whether low doses of inhaled corticosteroids are associated with an increased risk of cataract is not known. This study was undertaken to quantify the risk of cataract associated with the use of inhaled corticosteroids and assess whether there is a dose-response relation. Methods: A population based case-control study based on the General Practice Research Database in the United Kingdom. 15 479 people with cataract and 15 479 controls were matched for age, sex, practice, and observation period. Results: The crude odds ratio for the association between any recorded exposure to inhaled corticosteroids and cataract was 1.58 (95% CI 1.46 to 1.71), reduced to 1.10 (95% CI 1.00 to 1.20) after adjustment for systemic corticosteroid exposure and consultation rate. There was a dose-response relation, the adjusted odds ratio rising from 0.99 (95% CI 0.87 to 1.13) at daily doses up to 400 mg to 1.69 (95% CI 1.17 to 2.43) for daily doses greater than 1600 mg. The association was also stronger with increasing duration of use. Conclusion: Higher doses and longer duration of exposure to inhaled corticosteroids are associated with an increased risk of cataract. The lowest doses compatible with good control of airways disease should be used. The risk of cataract associated with high doses of inhaled corticosteroids needs to be more widely appreciated.

Cataract and age-related macular degeneration (AMD) are the major causes of vision impairment and blindness worldwide. Both conditions are strongly age related with earlier signs (usually asymptomatic) occurring in middle age and becoming severer and more prevalent with increasing age. The aetiology of these conditions is thought to fit with the ‘free radical theory’ of ageing which postulates that ageing and age-related diseases result from the accumulation of cellular damage from reactive oxygen species (ROS). Mitochondrial energy production is a major source of endogenous ROS. External sources of ROS include environmental sources especially solar radiation, biomass fuels and tobacco smoking. There is strong evidence from epidemiological studies that smoking is a risk factor for both cataract and AMD. There is moderate evidence for an association with sunlight and cataract but weak evidence for sunlight and AMD. The few studies that have investigated this suggest an adverse effect of biomass fuels on cataract risk. The antioxidant defence system of the lens and retina include antioxidant vitamins C and E and the carotenoids lutein and zinc, and there is mixed evidence on their associations with cataract and AMD from epidemiological studies. Most epidemiological studies have been conducted in well-nourished western populations but evidence is now emerging from other populations with different dietary patterns and antioxidant levels.

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In the short- and medium-term, statins do not seem to be associated with an increased risk of cataract. The need to assess the effects of long-term statin exposure on the eye remains.