Results
Table 1 shows the number of people in each age group in the study who were admitted to hospital with hypertension or diabetes; it shows the percentage of female subjects; and it shows the matching ratio which is the number of people in each age group in the reference cohort who were matched to each person in the hypertension or diabetes cohort. We used all eligible records on the data files for the 'controls' in the reference cohorts. Matching ratios were considerably higher in the very young than the older people but, because the analyses that follow are age standardised, the comparisons among the hypertension and diabetes cohorts and the reference cohorts are equivalenced in respect of age (in a stratified and standardised analysis of an existing dataset, no purpose is served by discarding control people to make a seemingly neat number of controls).
Hypertension
In people with hypertension, there was a numerically small, borderline significant, elevation of risk of cataract: the rate ratio, comparing the hypertension cohort with the reference cohort, was 1.15 (95% CI 1.00 to 1.31) in ORLS and 1.06 (1.01 to 1.10) in the national cohort (Table 2). The rate ratios for glaucoma were non-significant in the ORLS (0.89, 0.66 to 1.17) and borderline significant in the much larger English population (1.07, 1.00 to 1.14). These findings indicate that, if there is any real elevation of risk of cataract or glaucoma, it is very small in scale.
There was a fourfold elevation of risk of RAO (Table 2), significant in England though not significant in the very small numbers of the ORLS. There was a significant elevation of risk of RVO in both populations.
Hypertension was associated with an elevated risk of RD, significantly so in England (RR 1.52, 1.34–1.73) but not significant in ORLS (1.05, 0.60–1.72). Hypertension was also associated with a significant but modest elevation of risk of AMD in England (1.14, 1.02–1.27), and a similar level of risk without its attaining statistical significance in ORLS (1.27, 0.57–2.46).
Diabetes Mellitus
Diabetes mellitus was associated with a clear, unequivocal elevation of risk of cataract, consistent in both populations (rate ratio in ORLS 2.95, 2.75–3.16; England 2.30, 2.24–2.35), and of glaucoma (ORLS 2.47, 2.14–2.84; England 2.23, 2.15–2.30): see Table 3. Risks of RAO and RVO were very high in both populations (Table 3), as were risks of RD (eg, rate ratio 7.96, 7.63–7.80, in England) and AMD (3.46, 3.35–3.58 in England).