Date Published: April 25, 2019
Publisher: Public Library of Science
Author(s): Hisanori Miyashita, Natsuko Hatsusaka, Eri Shibuya, Norihiro Mita, Mai Yamazaki, Teppei Shibata, Hidetoshi Ishida, Yuki Ukai, Eri Kubo, Hiroshi Sasaki, Nobuyuki Hamada.
We investigated associations between ocular ultraviolet (UV) radiation exposure dose and cataract opacities among Han people living in China and Taiwan, to assess the effects of UV exposure intensity.
This cross-sectional study included Han people aged ≥40 years (1,801 individuals, 450 in Sanya, 636 in Taiyuan, and 715 in Taichung) as subjects who completed a questionnaire including items about diabetes, smoking, steroid use, work history, and time spent outdoors, and underwent an ophthalmic examination. Right eye axial length was measured using A-mode ultrasonography or IOLMaster. Slit-lamp imaging under maximum mydriasis was used to classify cataracts into three major types [cortical (COR), nuclear (NUC), and posterior subcapsular cataracts (PSC)] and two subtypes [retrodots (RD) and waterclefts (WC)] by one ophthalmologist. COR was divided into opacity presence (CEN+) or absence (CEN-) in the central 3-mm diameter area of the pupil. COR was also subdivided into three groups according to opacity shape: axle-shaped opacity concomitant with WC, wedge-shaped opacity around the pupil to the eye center, and ring-shaped opacity in the lens equator along the pupillary margin. The cumulative ocular UV exposure (COUV) was calculated. A logistic regression analysis was used for multivariate analysis.
Cataract odds ratios in high COUV eyes were 5.35 for NUC, 1.87 for PSC, and 1.35 for RD. In eyes with WC, risk of COR ring-shaped opacity significantly increased but that of wedge-shaped opacity (CEN+) significantly decreased. In eyes without WC, risk of COR axle-shaped opacity (CEN–) and ring-shaped opacity significantly increased but that of wedge-shaped opacity (CEN+) significantly decreased.
Increased COUV level among Han people may be a risk factor for the development of nuclear cataracts, PSC, retrodots and ring-shaped cortical cataract. Risk of ocular UV exposure for cortical cataract may differ by opacity shape.
Many studies have reported ultraviolet (UV) radiation to be a risk factor for cataract [1–3]. Although the onset of anterior cortical cataract has been reported to be caused by UVB exposure through some animal experiments [4–7], most reports have assessed the application of much stronger UVB exposure than the normal daily exposure dose. To the best of our knowledge, no reports have used an animal model to investigate the effects of long-term exposure to low-dose UVB. Giblin et al. previously reported on how long-term exposure to low-dose UVA induced the development of nuclear cataract (NUC) in a guinea pig model . Although many previous epidemiological studies have reported an association between cortical cataract (COR) and UV light [9–11], most of these studies were conducted in regions ranging from mid- to high-latitudes. To date, only a few studies have been conducted in low latitude regions with strong UV exposure. Some studies investigating NUC have reported no association with UV exposure [9, 12], in contrast, others have reported relationships between these factors [13–17]. In addition, some reports have indicated an association between UV exposure and posterior subcapsular cataract (PSC) . Retrodots (RD) and waterclefts (WC) are cataract subtypes that cause decreased visual function, with a high prevalence among middle-aged to elderly individuals [19, 20]. Because no studies have investigated associations between UV exposure and these types of cataract, their relationship with UV exposure remains unknown. Moreover, few reports have examined this relationship in a single race living in regions with different UV intensities.