For the past 10 years, the authors have performed cataract epidemiological surveys in several places. All of them were principally population based and applied new types of photodocumentation systems which were developed by our department. The survey places in Japan were Noto, our main survey field located in the centre of the main island of Japan, one village in the subtropical island of Okinawa, a village in the northern island of Hokkaido and one village (Bukittinggi) in West-Sumatra, Indonesia, very close to the equator. The survey methods applied including an interview and ophthalmological examinations, were almost identical in each place and the authors believe that the quality of the examinations was at high level. The cataract classification and grading systems applied were those established by the Japanese Co-operative Cataract Epidemiology Study Group. At present, no significant prominent difference of cataract prevalence and distribution of cataract types have been found in the three Japan survey places. The distribution of cataract types in the Indonesian subjects however, was different from the Japanese subjects. The lens transparency ratio in the Noto survey was quite similar to that of a Dutch study. From photographic images of both opaque and transparent lenses much objective information which be cannot detected through naked eye observation is obtainable. Furthermore, data obtained from the images are comparable because of their objectivity. Although the methodology seems to be rather sophisticated and is costly, the above advantages make it an important asset in this type of cataract research. For example, lens transparency changes with ageing can be indicated quantitatively from image analysis data.(ABSTRACT TRUNCATED AT 250 WORDS)