The relationship between cataract and climatic droplet keratopathy in Mongolia

This study evaluated the association between cataract, the commonest single blinding disorder worldwide, and climatic droplet keratopathy which was taken as an indicator of high exposure to ultraviolet sunlight. A sample of 4344 persons from rural Mongolia (1991-92) provided 8634 eyes for analysis of the relationship between cataract and climatic droplet keratopathy. Right and left eyes were combined (paired into matched sets), and analysed using a random-effects regression model. The results indicated an inverse association between cataract and climatic droplet keratopathy in person aged 55 years or older, whereby eyes with more advanced climatic droplet keratopathy had lower prevalence of cataract (age-adjusted odds ratio 0.53, p = 0.047). In the younger group of persons aged 40-54 years, the reverse was found, whereby cataract prevalence was higher in eyes that have climatic droplet keratopathy (age-adjusted odds ratio 13.19, p = 0.046). However, only a small proportion (4%) of all the cataracts occurred in this younger age stratum where the prevalence of cataract was 0.5%, compared to prevalence of 17% in eyes of persons aged 55 years or older. These findings cast further doubts upon the current thesis that lifetime exposure to high levels of ultraviolet sunlight is a major cause of cataract in developing countries.