Mortality and causes of death in a population with blindness in Korea: A longitudinal follow-up study using a national sample cohort

Abstract

The influence of visual impairment and blindness on the risk of mortality has been reported in diverse cohort studies. However, the results reported have varied from nonsignificant to significant associations. In the present study, we evaluated the influence of blindness on the risk of mortality from 2002 to 2013 using a longitudinal database with a national sample cohort provided by the Korean National Health Insurance Service. Of a total of 1,125,691 subjects, 1,279 subjects who were registered as blind were enrolled, and 5,116 control participants were matched at a 1:4 ratio for age, sex, income, region of residence, and medical histories of hypertension, diabetes mellitus and dyslipidemia. The life/death information contained in this dataset was used for the analysis; this information was originally recorded by the medical doctors on the death certificates of the participants. The percentage of total deaths during the mean follow-up period of 111.0 ± 41.6 months was 28.1% in the blindness group and 19.7% in the matched control group. The risk of mortality was significantly higher in the blindness group than in the control group according to the Cox proportional hazards model with additional adjustments for ischemic heart disease, stroke, and depression (adjusted hazard ratio [HR] of mortality = 1.54, 95% confidence interval [CI] = 1.37-1.74, P < 0.001). In the subgroup analyses, the adjusted HRs for mortality were significantly higher in the blindness group than in the control group regardless of age (young defined as <60 years old vs old defined as ≥60 years old) and sex. The percentage of death due to metabolic diseases and genitourinary diseases was higher in the blindness group than in the matched control group.

Figure 1

Kaplan–Meier survival curves for the blindness and control groups. The blindness group (green line) had a lower cumulative survival rate than the control group (blue line) (P < 0.001).

Figure 2

A flowchart of the participant selection process that was used in the present study. Out of a total of 1,125,691 participants, 1,292 participants with blindness were selected. The participants with blindness were matched at a 1:4 ratio with a control group that did not present visual impairment. Unmatched participants with blindness were excluded (n = 13). Finally, 1,279 participants with blindness and 5,116 control participants were included.