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BMC Ophthalmology

BioMed Central rj<-sfs  
Page 1 of 7 2%]#rZ  
(page number not for citation purposes) r&XxF >  
BMC Ophthalmology t"6u  
Research article Open Access ?W&ajH_T  
Comparison of age-specific cataract prevalence in two W7IAW7w8U  
population-based surveys 6 years apart @_h=,g #@  
Ava Grace Tan†, Jie Jin Wang*†, Elena Rochtchina† and Paul Mitchell† &7c#i  
Address: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital, 'RR,b*Ql  
Westmead, NSW, Australia t1aKq)?  
Email: Ava Grace Tan - ava_tan@wmi.usyd.edu.au; Jie Jin Wang* - jiejin_wang@wmi.usyd.edu.au; D6EqJ ,~  
Elena Rochtchina - elena_rochtchina@wmi.usyd.edu.au; Paul Mitchell - paul_mitchell@wmi.usyd.edu.au M/}i7oS]  
* Corresponding author †Equal contributors r \} O{ZO  
Abstract QwI HEmdM  
Background: In this study, we aimed to compare age-specific cortical, nuclear and posterior jgw+c3^R_  
subcapsular (PSC) cataract prevalence in two surveys 6 years apart. j*_#{niy:  
Methods: The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in SN#N$] y5s  
cross-section I (1992–4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in z'EphL7r   
cross-section II (1997–2000, 66.5% overlap with cross-section I). Cataract was assessed from lens `P;uPQDzZ3  
photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if *0 ;|  
cortical opacity comprised ≥ 5% of lens area. Nuclear cataract was defined if nuclear opacity ≥ |%=c<z+8  
Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons d,t'e?  
who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and OEHw%  
0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using sAP  YQ  
an interval of 5 years, so that participants within each age group were independent between the ?&.Eg^a"  
two surveys. RD*.n1N1  
Results: Age and gender distributions were similar between the two populations. The age-specific AT I2  
prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The <*$IZl6I  
prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization, 0ac'<;9]zP  
the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased 'S; l"  
prevalence of nuclear cataract (18.7%, 24.2%) remained. L$f:D2Ei  
Conclusion: In two surveys of two population-based samples with similar age and gender T- lHlm  
distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period. n4Eqm33  
The increased prevalence of nuclear cataract deserves further study. WiclG8l  
Background m=%WA5c?  
Age-related cataract is the leading cause of reversible visual {!7 ^ w  
impairment in older persons [1-6]. In Australia, it is F /% 5 r{  
estimated that by the year 2021, the number of people ?hwT{h  
affected by cataract will increase by 63%, due to population iKuSk~  
aging [7]. Surgical intervention is an effective treatment X{b qG]j  
for cataract and normal vision (> 20/40) can usually - +=+W  
be restored with intraocular lens (IOL) implantation. <hbxerg  
Cataract surgery with IOL implantation is currently the dD0:K3@  
most commonly performed, and is, arguably, the most O(oGRK<xM  
cost effective surgical procedure worldwide. Performance q!+m, !M  
Published: 20 April 2006 ;.P9t`*  
BMC Ophthalmology 2006, 6:17 doi:10.1186/1471-2415-6-17 K\]ey;Bd  
Received: 14 December 2005 i@}/KT  
Accepted: 20 April 2006 !mLY W  
This article is available from: http://www.biomedcentral.com/1471-2415/6/17 -hIDL'5u-I  
© 2006 Tan et al; licensee BioMed Central Ltd. RwC1C(ZP  
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), +TnRuehtk  
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 71ctjU`U2  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 } + 8w  
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of this surgical procedure has been continuously increasing Zn`vL52_  
in the last two decades. Data from the Australian W\?_o@d  
Health Insurance Commission has shown a steady sKT GZA  
increase in Medicare claims for cataract surgery [8]. A 2.6- GX+oA]  
fold increase in the total number of cataract procedures b4$-?f?V  
from 1985 to 1994 has been documented in Australia [9]. Gdd lB2L)x  
The rate of cataract surgery per thousand persons aged 65 4M&6q(389  
years or older has doubled in the last 20 years [8,9]. In the g6kVHxh-  
Blue Mountains Eye Study population, we observed a onethird k]=Yi;  
increase in cataract surgery prevalence over a mean =sk]/64h``  
6-year interval, from 6% to nearly 8% in two cross-sectional i#M$i*H*A  
population-based samples with a similar age range (@H'7,  
[10]. Further increases in cataract surgery performance pbe" w=<  
would be expected as a result of improved surgical skills IZV D.1  
and technique, together with extending cataract surgical {VPF2JFB[  
benefits to a greater number of older people and an JR1/\F<}  
increased number of persons with surgery performed on (0Xgv3wd  
both eyes. e?%Qv+)W  
Both the prevalence and incidence of age-related cataract 4%TY` II  
link directly to the demand for, and the outcome of, cataract x>^r%<WbX  
surgery and eye health care provision. This report TlD)E  
aimed to assess temporal changes in the prevalence of cortical %Bo/vB'  
and nuclear cataract and posterior subcapsular cataract LB|FVNW/S  
(PSC) in two cross-sectional population-based ).0h4oHSj  
surveys 6 years apart. !YlyUHD  
Methods 8kz7*AO  
The Blue Mountains Eye Study (BMES) is a populationbased >W= 0N (  
cohort study of common eye diseases and other <6=kwV6  
health outcomes. The study involved eligible permanent 6@T Ga%:G  
residents aged 49 years and older, living in two postcode 85P7I=`*d  
areas in the Blue Mountains, west of Sydney, Australia. !A(*?0`  
Participants were identified through a census and were g|r:+%,M  
invited to participate. The study was approved at each )6# i>c-  
stage of the data collection by the Human Ethics Committees !xm87I  
of the University of Sydney and the Western Sydney rULrGoM  
Area Health Service and adhered to the recommendations ULq#2l  
of the Declaration of Helsinki. Written informed consent 20G..>zW  
was obtained from each participant. v Dgf}  
Details of the methods used in this study have been K8{Ub  
described previously [11]. The baseline examinations |kL^k{=zV  
(BMES cross-section I) were conducted during 1992– S&jZYq**  
1994 and included 3654 (82.4%) of 4433 eligible residents. KXEDpr  
Follow-up examinations (BMES IIA) were conducted XOQj?Q7)U  
during 1997–1999, with 2335 (75.0% of BMES Hf( d x\5  
cross section I survivors) participating. A repeat census of {umdW x.*  
the same area was performed in 1999 and identified 1378 yjUSM}$  
newly eligible residents who moved into the area or the [bd fp a  
eligible age group. During 1999–2000, 1174 (85.2%) of d(RSn|[0  
this group participated in an extension study (BMES IIB). kYwk'\s  
BMES cross-section II thus includes BMES IIA (66.5%) sfSM7f  
and BMES IIB (33.5%) participants (n = 3509). .!T]sX_P  
Similar procedures were used for all stages of data collection ?ic7M  
at both surveys. A questionnaire was administered qF m=(J%  
including demographic, family and medical history. A HCHZB*r[  
detailed eye examination included subjective refraction, {8Jr.&Y2  
slit-lamp (Topcon SL-7e camera, Topcon Optical Co, KD9Y  
Tokyo, Japan) and retroillumination (Neitz CT-R camera, ]K'iCYY  
Neitz Instrument Co, Tokyo, Japan) photography of the 2 fp\s5%J}  
lens. Grading of lens photographs in the BMES has been tmF->~|  
previously described [12]. Briefly, masked grading was ,>X +tEgR  
performed on the lens photographs using the Wisconsin g3@Qn?(j!  
Cataract Grading System [13]. Cortical cataract and PSC iOI8'`mk  
were assessed from the retroillumination photographs by _idTsd:\  
estimating the percentage of the circular grid involved. j_ dCy  
Cortical cataract was defined when cortical opacity VmM?KlC  
involved at least 5% of the total lens area. PSC was defined d4h1#MK  
when opacity comprised at least 1% of the total lens area. V=}AFGC85  
Slit-lamp photographs were used to assess nuclear cataract eyK=F:GO  
using the Wisconsin standard set of four lens photographs <`8l8cL  
[13]. Nuclear cataract was defined when nuclear opacity Wh4`Iv \.  
was at least as great as the standard 4 photograph. Any cataract k^-HY[Q9  
was defined to include persons who had previous a=3?hVpB  
cataract surgery as well as those with any of three cataract rJ)O(  
types. Inter-grader reliability was high, with weighted =H&@9=D*  
kappa 0.82 for cortical cataract, 0.55 (simple kappa 0.75) {R b|";  
for nuclear cataract and 0.82 for PSC grading. The intragrader yD6lzuk{X  
reliability for nuclear cataract was assessed with N0EJHS,>e  
simple kappa 0.83 for the senior grader who graded Yhu 6QyRV  
nuclear cataract at both surveys. All PSC cases were confirmed z7X[$T$V  
by an ophthalmologist (PM). #Pi}2RBRu  
In cross-section I, 219 persons (6.0%) had missing or ,&$w*D%  
ungradable Neitz photographs, leaving 3435 with photographs 7XLz Ewa  
available for cortical cataract and PSC assessment,  w.kb/  
while 1153 (31.6%) had randomly missing or ungradable H2oAek(  
Topcon photographs due to a camera malfunction, leaving "NqB_?DT  
2501 with photographs available for nuclear cataract p-QD(+@M  
assessment. Comparison of characteristics between participants nJH+P!AC  
with and without Neitz or Topcon photographs in *gHGi(U(U  
cross-section I showed no statistically significant differences 48 DC  
between the two groups, as reported previously Z3Le?cMt^  
[12]. In cross-section II, 441 persons (12.5%) had missing S0+nQM%  
or ungradable Neitz photographs, leaving 3068 for cortical !Oj]. WQ  
cataract and PSC assessment, and 648 (18.5%) had {L 7O{:J  
missing or ungradable Topcon photographs, leaving 2860 !o A,^4(  
for nuclear cataract assessment. @ %LrpD  
Data analysis was performed using the Statistical Analysis v{7Jzjd  
System (SAS, SAS Institute, Cary, NC, USA). Age-adjusted <0!/7*;#ZT  
prevalence was calculated using direct standardization of (h;4irfX  
the cross-section II population to the cross-section I population. Ik_u34U  
We assessed age-specific prevalence using an /DPD,bA  
interval of 5 years, so that participants within each age 5e^t;  
group were independent between the two cross-sectional Z["[^=EP  
surveys. XD>(M{~  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 f=%k9Y*)  
Page 3 of 7 ]+RBykr  
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Results 7VWq8FH`  
Characteristics of the two survey populations have been :]&O  
previously compared [14] and showed that age and sex t e e  
distributions were similar. Table 1 compares participant >U/ m/H'  
characteristics between the two cross-sections. Cross-section tE"aNA#=  
II participants generally had higher rates of diabetes, 1an?/j,  
hypertension, myopia and more users of inhaled steroids. i@7b  
Cataract prevalence rates in cross-sections I and II are &m @~R|  
shown in Figure 1. The overall prevalence of cortical cataract E3bS Q  
was 23.8% and 23.7% in cross-sections I and II, vb 2mY  
respectively (age-sex adjusted P = 0.81). Corresponding px!lJtvgo  
prevalence of PSC was 6.3% and 6.0% for the two crosssections R7xKVS_MP  
(age-sex adjusted P = 0.60). There was an zNe>fZ  
increased prevalence of nuclear cataract, from 18.7% in SF?Ublc!   
cross-section I to 23.9% in cross-section II over the 6-year -*;-T9  
period (age-sex adjusted P < 0.001). Prevalence of any cataract DQ'yFPE  
(including persons who had cataract surgery), however, YKF5|;}  
was relatively stable (46.9% and 46.8% in crosssections gJYB)LjH"  
I and II, respectively). <3aiS?i.h  
After age-standardization, these prevalence rates remained o[C,fh,$  
stable for cortical cataract (23.8% and 23.5% in the two ,9T-\)sT  
surveys) and PSC (6.3% and 5.9%). The slightly increased )TNAgTmqK  
prevalence of nuclear cataract (from 18.7% to 24.2%) was GjDs,9@f  
not altered. mj\]oWS7d  
Table 2 shows the age-specific prevalence rates for cortical _M.7%k/U8  
cataract, PSC and nuclear cataract in cross-sections I and |etA2"r&  
II. A similar trend of increasing cataract prevalence with 6I,^4U  
increasing age was evident for all three types of cataract in tbbZGyg5b  
both surveys. Comparing the age-specific prevalence N7/eF9  
between the two surveys, a reduction in PSC prevalence in Y", :u@R  
cross-section II was observed in the older age groups (≥ 75 \F_~?$  
years). In contrast, increased nuclear cataract prevalence >lZ9Y{Y4v  
in cross-section II was observed in the older age groups (≥ N_#QS}H  
70 years). Age-specific cortical cataract prevalence was relatively x'Uv;mGo  
consistent between the two surveys, except for a +k@$C,A  
reduction in prevalence observed in the 80–84 age group 1: cD\  
and an increasing prevalence in the older age groups (≥ 85 85$W\d  
years). nJEm&"AI  
Similar gender differences in cataract prevalence were lLq9)+HGN  
observed in both surveys (Table 3). Higher prevalence of KHK|Zu#k '  
cortical and nuclear cataract in women than men was evident #=>t6B4af  
but the difference was only significant for cortical PjL"7^Q&  
cataract (age-adjusted odds ratio, OR, for women 1.3, } v#Tm  
95% confidence intervals, CI, 1.1–1.5 in cross-section I (`z`ni  
and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con- M oIq)5/  
Table 1: Participant characteristics. |2oCEb1  
Characteristics Cross-section I Cross-section II /eZ UAxq  
n % n % q-3,p.  
Age (mean) (66.2) (66.7) n\ l$R!zr  
50–54 485 13.3 350 10.0 l $j/Ye]  
55–59 534 14.6 580 16.5 qXI>x6?*  
60–64 638 17.5 600 17.1 "oZ$/ap\  
65–69 671 18.4 639 18.2 )U>JFgpIW  
70–74 538 14.7 572 16.3 (]wd8M  
75–79 422 11.6 407 11.6 cjTV~(i'4A  
80–84 230 6.3 226 6.4 L.5 /wg  
85–89 100 2.7 110 3.1 j?5s/  
90+ 36 1.0 24 0.7 0vu$d xb[  
Female 2072 56.7 1998 57.0 s<}d)L(  
Ever Smokers 1784 51.2 1789 51.2 z?9vbx  
Use of inhaled steroids 370 10.94 478 13.8^ u0Nag=cU  
History of: U{^~X_?  
Diabetes 284 7.8 347 9.9^ v6Vd V.BI  
Hypertension 1669 46.0 1825 52.2^ p5 !B  
Emmetropia* 1558 42.9 1478 42.2 nhbCk6Y5LZ  
Myopia* 442 12.2 495 14.1^ m2j&v$  
Hyperopia* 1633 45.0 1532 43.7 dIQxU  
n = number of persons affected y;M}I8W[  
* best spherical equivalent refraction correction f{m,?[1C,  
^ P < 0.01 ?9F_E+!  
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t o~ v   
rast, men had slightly higher PSC prevalence than women +Wr"c  
in both cross-sections but the difference was not significant 2HxT+|~d6  
(OR 1.1, 95% CI 0.8–1.4 for men in cross-section I ?1DA  
and OR 1.2, 95% 0.9–1.6 in cross-section II). F|rJ{=x  
Discussion R{GT? wl  
Findings from two surveys of BMES cross-sectional populations >u6*P{;\  
with similar age and gender distribution showed :^G;`T`L  
that the prevalence of cortical cataract and PSC remained 2l7Sbs7  
stable, while the prevalence of nuclear cataract appeared 7wO0d/l_  
to have increased. Comparison of age-specific prevalence, k|O?qE1hP  
with totally independent samples within each age group, B4/0t:^I  
confirmed the robustness of our findings from the two *%{  
survey samples. Although lens photographs taken from u:6PAVW?  
the two surveys were graded for nuclear cataract by the 5|4=uoA<  
same graders, who documented a high inter- and intragrader Ql%0%naq1  
reliability, we cannot exclude the possibility that Vy+%sG q"  
variations in photography, performed by different photographers, X2 Z E9b  
may have contributed to the observed difference R%(ww  
in nuclear cataract prevalence. However, the overall JTK0#+?  
Table 2: Age-specific prevalence of cataract types in cross sections I and II. r`; "   
Cataract type Age (years) Cross-section I Cross-section II 4yk!T  
n % (95% CL)* n % (95% CL)* P ~pC /z  
Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2) -w0U }Te^  
55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5) ~J U :a@)  
60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8) g^CAT1}  
65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0) BQs~>}(V  
70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6) Z[(V0/[]  
75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1) d%"?^ e  
80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6) qtx5N)J6  
85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5) U%Igj:%?;`  
90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2) _n[4+S*v(  
PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0) DeMF<)#  
55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9) ) <lpI';T  
60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6) V4('}Q!  
65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3) zF& >1y.$  
70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3) 1pUIZ$@?`  
75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7) mXX9Aa>  
80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2) .szs?  
85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4) >=|;2*9v  
90+ 23 21.7 (3.5–40.0) 11 0.0 ,| \62B`  
Nuclear 50–54 323 1.6 (0.2–2.9) 331 0.9 (–0.2–1.9) xk1pZQ8c  
55–59 386 2.3 (0.8–3.8) 507 3.6 (1.9–5.2) 1I'ep\`"X  
60–64 453 5.3 (3.2–7.4) 501 11.6 (8.8–14.4) ZQd\!K8y^Q  
65–69 478 17.2 (13.8–20.1) 534 18.5 (15.2–21.9) \"E-z.wW=  
70–74 392 27.6 (23.1–32.0) 453 36.0 (31.6–40.4) STC'j1U  
75–79 255 45.1 (39.0–51.3) 302 55.6 (50.0–61.3) lL*k!lNs  
80–84 146 54.1 (45.9–62.3) 147 73.5 (66.3–80.7) Vd8BQB,Q  
85–89 50 64.0 (50.2–77.8) 70 80.0 (70.4–89.6) G 4jaHpPi  
90+ 18 72.2 (49.3–95.1) 15 73.3 (48.0–98.7) BjT0m k"P  
n = number of persons nFVQOr;  
* 95% Confidence Limits Qi_De '@  
Cataract FMioguunrtea i1n ps rEeyvea lSetnucdey in cross-sections I and II of the Blue IZ2c<B5&  
Cataract prevalence in cross-sections I and II of the Blue ` "Gd/  
Mountains Eye Study. G(alM=q  
0 =Vgj=19X(  
10 }y-b<J ?H  
20 -L9I;]:KY  
30 oSb,)k@  
40 Wr\rruH6  
50 :v_H;UU  
cortical PSC nuclear any F5CV<-jB  
cataract );LkEXC_'  
Cataract type pGZ I697  
% Bn7~p+N  
Cross-section I =6mnXpM.  
Cross-section II ToUeXU [  
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Page 5 of 7 DU6AlNx  
(page number not for citation purposes) t 3TnqA  
prevalence of any cataract (including cataract surgery) was 0Ywqv)gg  
relatively stable over the 6-year period. 0@R @L}m  
Although different population-based studies used different J%?'Q{  
grading systems to assess cataract [15], the overall *$ZLu jy7  
prevalence of the three cataract types were similar across 83*"58  
different study populations [12,16-23]. Most studies have *D: wwJ  
suggested that nuclear cataract is the most prevalent type G)A5;u\P9  
of cataract, followed by cortical cataract [16-20]. Ours and DrD68$,QN  
other studies reported that cortical cataract was the most :/HfMJ  
prevalent type [12,21-23]. /aepE~T  
Our age-specific prevalence data show a reduction of D0?l$]aE  
15.9% in cortical cataract prevalence for the 80–84 year Ybr&z7# 2  
age group, concordant with an increase in cataract surgery lGa'Y  
prevalence by 9% in those aged 80+ years observed in the LTsG  
same study population [10]. Although cortical cataract is 6x*u S~'  
thought to be the least likely cataract type leading to a cataract h9)QQPP  
surgery, this may not be the case in all older persons. U?u0|Y+  
A relatively stable cortical cataract and PSC prevalence $ctY#:;pV{  
over the 6-year period is expected. We cannot offer a I|=$.i  
definitive explanation for the increase in nuclear cataract _"8\k 7S*  
prevalence. A possible explanation could be that a moderate pq`Bg`c  
level of nuclear cataract causes less visual disturbance $x&\9CRM  
than the other two types of cataract, thus for the oldest age !BHIp7p  
groups, persons with nuclear cataract could have been less Zy2@1-z6  
likely to have surgery unless it is very dense or co-existing SSANt?\Z<  
with cortical cataract or PSC. Previous studies have shown CB5 ~!nKv&  
that functional vision and reading performance were high $wa )e  
in patients undergoing cataract surgery who had nuclear iw|6w,-)C  
cataract only compared to those with mixed type of cataract i)V-q9\  
(nuclear and cortical) or PSC [24,25]. In addition, the jV^Dj  
overall prevalence of any cataract (including cataract surgery) Hh=D:kE  
was similar in the two cross-sections, which appears jP6;~[rl  
to support our speculation that in the oldest age group, |[x) %5F  
nuclear cataract may have been less likely to be operated }Y(yDg;"  
than the other two types of cataract. This could have LEMgRI`rf  
resulted in an increased nuclear cataract prevalence (due w$*t.Q*  
to less being operated), compensated by the decreased y 1fl=i  
prevalence of cortical cataract and PSC (due to these being &UG7 g  
more likely to be operated), leading to stable overall prevalence ~:."BA  
of any cataract. $l:?(&u  
Possible selection bias arising from selective survival I(E1ym  
among persons without cataract could have led to underestimation )J+vmY~&  
of cataract prevalence in both surveys. We 9viQ<}K<  
assume that such an underestimation occurred equally in /ve8);cH\  
both surveys, and thus should not have influenced our H".~@,-}  
assessment of temporal changes. 'j];tO6GfC  
Measurement error could also have partially contributed 1c  S{3  
to the observed difference in nuclear cataract prevalence. _Tyj4t0ElV  
Assessment of nuclear cataract from photographs is a @Nb&f<+gi  
potentially subjective process that can be influenced by mP GF Y  
variations in photography (light exposure, focus and the )K\w0sjR  
slit-lamp angle when the photograph was taken) and Y[x9c0  
grading. Although we used the same Topcon slit-lamp Ftj3` Mu  
camera and the same two graders who graded photos u79.`,Ad&  
from both surveys, we are still not able to exclude the possibility 6sl*Ko[  
of a partial influence from photographic variation G8"L #[~  
on this result. ;<%~g8:XL  
A similar gender difference (women having a higher rate $@q)IK%FDL  
than men) in cortical cataract prevalence was observed in 5B| iBS l  
both surveys. Our findings are in keeping with observations |SXMd'<3`Z  
from the Beaver Dam Eye Study [18], the Barbados iUqL /  
Eye Study [22] and the Lens Opacities Case-Control ]t]s/;9]K  
Group [26]. It has been suggested that the difference z (rQ6  
could be related to hormonal factors [18,22]. A previous |/zE(ePc{  
study on biochemical factors and cataract showed that a mY2 Ubn*  
lower level of iron was associated with an increased risk of 5SFeJBS  
cortical cataract [27]. No interaction between sex and biochemical ~h?zK 1  
factors were detected and no gender difference 9>d$a2 nc  
was assessed in this study [27]. The gender difference seen cEO g  
in cortical cataract could be related to relatively low iron #)_4$<P*'  
levels and low hemoglobin concentration usually seen in h9LA&!  
women [28]. Diabetes is a known risk factor for cortical ~: Dr]kt  
Table 3: Gender distribution of cataract types in cross-sections I and II. `TKe+oS)  
Cataract type Gender Cross-section I Cross-section II v"6q!  
n % (95% CL)* n % (95% CL)* PMjqcdBzm  
Cortical Male 1496 21.1 (19.0–23.1) 1328 20.4 (18.2–22.6) F)) +a&O  
Female 1939 25.9 (23.9–27.8) 1785 26.2 (24.2–28.3) >F6'^9|  
PSC Male 1500 6.5 (5.2–7.7) 1314 6.4 (5.1–7.7) zCj]mH`es'  
Female 1944 6.2 (5.1–7.2) 1753 5.7 (4.6–6.7) }'a}s0h  
Nuclear Male 1106 17.6 (15.4–19.9) 1225 22.5 (20.1–24.8) eiI}:5~ /g  
Female 1395 19.5 (17.4–21.6) 1635 25.0 (22.9–27.1) =9FY;9  
n = number of persons rgdDkWLXC  
* 95% Confidence Limits )U e9:e  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 BftW<1,U^  
Page 6 of 7 ` *x;&.&v  
(page number not for citation purposes) >%x7-->IB  
cataract but in this particular population diabetes is more "zJ1vIZY  
prevalent in men than women in all age groups [29]. Differential gI6./;;x  
exposures to cataract risk factors or different dietary U-#wFc2N  
or lifestyle patterns between men and women may _C DUUr  
also be related to these observations and warrant further +rfw)c'  
study. L0Bcx|)"$`  
Conclusion z{Z'2, #  
In summary, in two population-based surveys 6 years u.x>::i&  
apart, we have documented a relatively stable prevalence qd(C%Wk  
of cortical cataract and PSC over the period. The observed R2yiExw<  
overall increased nuclear cataract prevalence by 5% over a X zgJ@  
6-year period needs confirmation by future studies, and q+5g+9  
reasons for such an increase deserve further study. ;*5$xs&=_Z  
Competing interests !#` .Mv Z  
The author(s) declare that they have no competing interests. o( Yfnnuy  
Authors' contributions vmm#UjwF3  
AGT graded the photographs, performed literature search r) ;U zd  
and wrote the first draft of the manuscript. JJW graded the {Y6U%HG{{r  
photographs, critically reviewed and modified the manuscript. DKnjmZ:J|  
ER performed the statistical analysis and critically A^nB!veh  
reviewed the manuscript. PM designed and directed the / CEnyE/  
study, adjudicated cataract cases and critically reviewed #kjN!S*=  
and modified the manuscript. All authors read and @?lmho?  
approved the final manuscript. d,AEV_  
Acknowledgements m1H_kJ  
This study was supported by the Australian National Health & Medical wO9|_.Z{  
Research Council, Canberra, Australia (Grant Nos 974159, 991407). The E j`  
abstract was presented at the Association for Research in Vision and Ophthalmology z)p( l!  
(ARVO) meeting in Fort Lauderdale, Florida, USA, May 2005. q{~59{Fha  
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