Ultraviolet B exposure and type of lens opacity in ophthalmic patients in Japan

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Abstract

Over the course of an individual's lifetime, lens fiber cells proliferate and differentiate to form various parts of the lens. The specific pathogenic effects of ultraviolet B radiation (UVB), one of the major causes of cataracts, may differ depending upon the particular part of the lens. In this study, the association of UVB exposure with specific types of lens opacity was investigated in relation to lifetime cumulative exposure, and was confirmed by subjects’ ages at exposure. The severity of lens opacities was assessed by slit lamp examination after pupil dilatation. Information on UVB exposure based on place of residence and average hours spent outdoors per day was obtained by interview for several age ranges of exposure. The effects of UVB exposure on cortical and nuclear opacities for both sexes were evaluated using logistic regression analysis. The severity of opacities was found to increase with UVB exposure. In particular, lifetime cumulative UVB exposure and exposure after the teenage years correlated with the presence of nuclear opacities in females. The results indicate that the effect of UVB exposure is greater for nuclear than for cortical opacities. This is in agreement with the proposed type-specific mechanism for lens opacities caused by UVB exposure.

Introduction

Cataracts have become a serious public health concern. In Japan, patients with cataracts comprise more than one-third of all ophthalmic patients (Statistics and Information Department, Japan, 1999). Many factors have been related to the induction of lens opacities and cataracts. Of these, ultraviolet radiation (UV) has received particular attention in recent years. UV can be classified into three broad wavelength regions: UVA at 315–400 nm, UVB at 280–315 nm, and UVC at 100–280 nm. Although the lens almost completely absorbs UVA, lens epithelial cells are especially sensitive to UVB-induced damage (Andley et al., 1994, Cejkova and Lojda, 1963). It has been established that UVB induces lens opacities in animal studies (Cejkova and Lojda, 1963, Pitts et al., 1977, Soderberg, 1988, Soderberg, 1991). However, the results of epidemiological studies in humans have not been in universal agreement (Hollow and Moran, 1981, Hiller et al., 1986, Collman et al., 1988, Taylor et al., 1988, Bochow et al., 1989, Dolezal et al., 1989, Cruickshanks et al., 1992, Sasaki et al., 1995, Hayashi et al., 1998a).

It has been suggested that the effects of UVB exposure differ between acute high-dose and chronic low-dose exposures (Lerman, 1982). Furthermore, as lens fibers proliferate and differentiate over the course of an individual's lifetime, the mechanisms of opacification in different parts of the lens may differ. It is possible that exposure over certain age ranges induces predominant types of lens opacities; if this were the case, a correlation between cataract type and UVB exposure would not be readily detectable when analyzing only cumulative or present exposure. However, to investigate the effects of UVB exposure, some previous studies have used the dose of present exposure (Hollow and Moran, 1981, Hiller et al., 1986, Sasaki et al., 1995, Hayashi et al., 1998a), and others have used lifetime cumulative exposure (Collman et al., 1988, Taylor et al., 1988, Bochow et al., 1989, Cruickshanks et al., 1992, Dolezal et al., 1989) as the exposure indices. Insufficient information on age at the time of UVB exposure may contribute to the disagreement among the previous epidemiological studies. To clarify the effects of UVB on lens opacities, it may be necessary to discriminate differential effects of UVB on distinct parts of the lens, and to separate UVB exposure in youth from that in later in life.

In our preliminary study, the effect of UVB exposure between the ages of 20 and 50 was shown to be greater for nuclear opacities than for cortical opacities (Hayashi, 1998). The purpose of the present study is to further confirm the effects of UVB exposure on distinct types of lens opacity.

Section snippets

Study subjects

This survey was conducted at the Department of Ophthalmology, Koshigaya Hospital, Dokkyo University, from July 1, 1997 to April 30, 1999. Koshigaya is located in 10 Km north of Tokyo, and is made up of urban areas (bed towns for workers commuting to Tokyo) interspersed with agricultural areas. The study subjects were all patients, 50 years-of-age or older, who were admitted for cataract surgery. Out-patients who were 50 years-of-age or more and who visited the outpatient ophthalmology clinic on

Results

Measurements of the reproducibility of UVB exposure information yielded κ coefficients of 0.8–0.9 for residence in each exposure-age range, and κ coefficients of 0.7–0.8 for average hours spent outdoors per day in each exposure-age range.

Table 3 shows the crude and multivariate-adjusted odds ratios for the effects of lifetime cumulative UVB dose and for that of UVB dose in each exposure-age range for the cortical group. Almost all the odds ratios were greater than 1.0. In particular, the crude

Discussion

These results reveal that lifetime cumulative UVB exposure, especially after the teenage years, significantly correlates with the severity of nuclear opacity in female patients. The effect of UVB exposure was greater for nuclear than for cortical opacities, which confirms the hypothesis that the effects of UVB exposure on lens opacities of different types are not identical. The effect of UVB exposure was also greater in females than in males.

UVB may induce opacities in distinct parts of the

Conclusion

The results of this study indicate that the effect of UVB exposure, especially after the teenage years, is greater on nuclear opacity than on cortical opacity. This finding is in agreement with the proposed type-specific effect of UVB exposure on lens opacity. Further investigation of UVB exposure, type of lens opacity, sex, and race is strongly warranted.

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