| Summary: | 博士 === 國立臺灣大學 === 公共衛生學系 === 85 === In Taiwan, cataracts are very common among the elderly but
its epi-demiologic studies are rare. In order to have our
own research on cataract, a valid,reproducible, and easily-
used cataract classification system is essential.Hence, the
very first session of the study was to assess the reliability
of theLens Opacities Classification System III (LOCS
III). Three raters(ophthalmologists with 10-15 years of
practice) examined 30 patients (60 eyes)and graded their lens
opacities independently accordi ng to LOCS III. Highinter-
rater reliability (ICC: Intra-class coefficient between.75
and.89) wasobtained on photographic grading. Lower grading with
clinical scores (.5 lower)was observed compared with the
photographic grading for the same rater. Thephotographic
variation was considered to be partially contributory to
thisdifference. Although photographic records are ideal for a
longitudinal study,clinical grading should not be omitted
and is superior to the photographicgrading. Our results also
in dicated that raters tended to give the same scoresfor nuclear
opacities and color. We postulate that this phenomena may be
due tothe fact that LOCS III puts nuclear opacities and
color in the same frame.Separate pictures are recommended to
avoid this problem. The second session of the study was to
conduct a survey in Fushing Townshipof Taoyuan. Type-specific
prevalence was aimed. Ethnic difference (aboriginesvs. non-
aborigines) in cataract prevalence was examined. In 1995 and
1996, atotal of 180 residents were recruited for this study.
Lens Opacities System III(LOCS III) was used to classify
cataracts. The overall prior cataract surgeryrate was 13.9%
with a significant increase with age (p<.0001). In
thoseindividuals with significant lens opacities , bilateral
was more commonly seenthan unilateral. Similar proportions of
nuclear (NU) alone (6.1%), cortical (CO)alone (7.3%), NU + CO
combined (7.3%), or all 3 (9.7%) were found in the sample.
Posterior subcapsular cataract opacities (PSC) alone
(1.2%) and CO + PSCcombined (1.2%) were less common while
NU + PSC combined was not seen. Theprevalence of NU, CO,
and PSC was 23.2%, 25.6% and 12.2%, respectively.
Significant gender difference was seen in the NU group
(p=.0358) but not in theCO or PSC types . The overall
prevalence of lens opacities, plus a bestcorrected visual
acuity (BVA) <=0.4, or plus a BVA <=0.1 were 32.9%, 13.4%,
or9.8%, respectively. Adding those patients who had prior
cataract surgery, theoverall prevalence increased another 10%.
No difference in any lens opacitiesand visual impaired cataract
was seen between aborigines and non-aborigines. Adose response
relationship between sunlight exposure and age-and sex-
adjustedcataract rate was observed, but the association
was not statisti callysignificant. The third session of
the study was to examine arsenic effect on cataract,which
never been investigated, using a cohort with a high exposure
to ingestedinorganic arsenic. In 1996, a total of 349 residents
were studied in this study.Lens Opacities System III (LOCS III)
was used to classify form of cataract. Theoverall cataract
surgery rate was 10% for the group aged 50+, and
increasedsignificantly with age (p<.0001). Cortical opacities
(CO) (35%) was the mostcommon type, while nuclear (NU) and p
osterior subcapsular (PSC) opacities wereseen in one-forth of
the sample, respectively. There was no gender difference inNU,
CO, and PSC. Diabetes mellitus (DM) was a significant risk for
cataract, NU,CO, and PSC. Occupational sunlight exposure was
positively associated with CO,showing multivariate-adjusted
odds ratios (OR) of 2.4 (95% CI=1.1-5.2) and 3.4(95%
CI=1.3-8.7) for individuals with 20-40 and >40 years of
occupation sunlightexposure, respectively. Cumulative arsenic
exposure shows a dose-resp onserelationship with prevalence
of PSC. Multivariate-adjusted ORs were 4.8 (95%CI=1.03-22.2)
and 5.7 (95% CI=1.2-26.3) for those with cumulative
arsenicexposures of 12.1-20 and >20 mg/L-years, respectively.
Although there are only several studies which use the
blood data toinvestigate an association between selenium
and cataract in humans, theirresults are controversial. The
fourth session of the study to use a veryhomogeneous
sample (narrow age range, healthy, from the same
geographiclocation) to explore the relationship between blood
selenium and cataract. In1996, a total of 74 study subjects
(41 cases and 33 controls) were recruitedfrom an elderly club.
Plasma selenium was measured by hydride atomic
absorptionspectrometry. Cataract was defined based on the Lens
Opacities ClassificationSystem III. Control subjects were
slightly younger than case subjects. Othercharacteristics,
including gender, cigarette smoking, use of alcohol,
andoccupational sunlight exposure, were comparable between
case and controlsubjects. Selenium level was categorized
into three groups: low portion lessthan.115 (g/ml, middle
portion between.115 and.135 (g/ml, and high portiongreater
than.135 (g/ml. A U-shaped r elation was seen between plasma
seleniumand overall cataract. Significantly high risk for
overall cataract was seen inindividuals with the low portion
than those with the middle portion of plasmaselenium (adjusted
OR=3.22 with 95% CI=1.01-10.38). U-shaped relation was alsoseen
in nuclear opacities (NU), cortical opacities (CO) and
posteriorsubcapsular opacities (PSC), but only PSC shows
statistical significance. TheORs of PSC were 4.70 (95% CI=1.16
- 19.05) and 4.57 (95% CI=1.05 - 19.94) forthe low a nd
high portion as compared to the middle portion. After
acomprehensive review on the relevant articles, we speculate
that not taking theU-shaped relationship into account may
be part of the reason of thecontroversial findings among
these studies. Bigger sample size, selenium levelin other
ocular tissue, nested case-control well help to clarify
therelationship between selenium and cataract.
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