The physiological ageing changes of decreasing lens transparency were objectively evaluated in a total of 1,040 eyes selected from 1,685 individuals who were the subjects of population-based cataract epidemiological surveys performed in three climatically different survey fields in Japan. The lens transparency changes were evaluated from the light scattering intensity on thirteen different lens layers seen in slit images taken by the latest type of Scheimpflug camera. The mean percentage prevalence of cataracts in all the epidemiological survey subjects including grading from I to III, which was also judged objectively through documented images, was 64.6% in the Noto subjects, 46.6% in the Hokkaido subjects and 38.0% in the Okinawa subjects. The lens transparency at all of the measuring points decreased with ageing. The above changes, seen in the lenses of subjects in their 40s to 60s, were obviously more prominent compared with those seen in subjects in their 40s. Although there were some differences in transparency decrease with ageing among the subjects of the three areas, the authors tentatively propose to show the data obtained from the Noto subjects as representative of Japanese individuals. Lens transparency changes on each lens layer showed characteristic ageing changes and those of the representative four layers showed an exponential decrease in transparency. The decreasing ratio might accelerate from age as early as the mid-40s.
To quantitatively evaluate nuclear lens opacification, we applied image analysis techniques. Utilizing a newly developed anterior eye segment analysis system, Scheimpflug slit images were taken in 65 eyes with transparent lenses and 31 eyes with nuclear cataract. In transparent lenses, scattering light intensity of the anterior fetal nucleus (AFN) was equal to or less than that of the posterior fetal nucleus (PFN). In eyes with nuclear cataract, scattering light intensity of the AFN was higher than that of the PFN. Utilizing this phenomenon, nuclear opacification was evaluated by the difference of scattering light intensity between the AFN and PFN (▵i value). The methodology applied in this investigation provides precise grading of nuclear cataract and progression thereof.
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