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BMC Ophthalmology

BioMed Central \ #N))gAQ  
Page 1 of 7 $IqubC>O  
(page number not for citation purposes) av bup  
BMC Ophthalmology 2B " tT"f  
Research article Open Access 8@/MrEOW#  
Comparison of age-specific cataract prevalence in two DWS#q|j`"  
population-based surveys 6 years apart 3oV2Ek<d  
Ava Grace Tan†, Jie Jin Wang*†, Elena Rochtchina† and Paul Mitchell† z.^_;Vql_  
Address: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital, LqLhZBU9  
Westmead, NSW, Australia OAaLCpRp  
Email: Ava Grace Tan - ava_tan@wmi.usyd.edu.au; Jie Jin Wang* - jiejin_wang@wmi.usyd.edu.au; n#sK31;yb  
Elena Rochtchina - elena_rochtchina@wmi.usyd.edu.au; Paul Mitchell - paul_mitchell@wmi.usyd.edu.au X\kWJQ:  
* Corresponding author †Equal contributors S`Z[MNY  
Abstract ,H_d#Koa.  
Background: In this study, we aimed to compare age-specific cortical, nuclear and posterior R'pfA B|!  
subcapsular (PSC) cataract prevalence in two surveys 6 years apart. h; 6G~D  
Methods: The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in AH? [K,3  
cross-section I (1992–4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in qP-_xpu]R  
cross-section II (1997–2000, 66.5% overlap with cross-section I). Cataract was assessed from lens "wCx]{Di  
photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if v\E6N2.S  
cortical opacity comprised ≥ 5% of lens area. Nuclear cataract was defined if nuclear opacity ≥ vdigw.=z  
Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons {|'NpV  
who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and B4*uS (  
0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using NK c<nYdK?  
an interval of 5 years, so that participants within each age group were independent between the _5S||TuNS  
two surveys.  uAs!5h  
Results: Age and gender distributions were similar between the two populations. The age-specific K' B*D*w  
prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The _2{2Xb  
prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization, _SkiO }c8  
the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased &DjA?0`J  
prevalence of nuclear cataract (18.7%, 24.2%) remained. u}P:9u&h6X  
Conclusion: In two surveys of two population-based samples with similar age and gender fhyoSRLR:  
distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period. W.%p{wB |  
The increased prevalence of nuclear cataract deserves further study. B@S~v+Gr  
Background YkE_7r(1  
Age-related cataract is the leading cause of reversible visual 5V~vND* s  
impairment in older persons [1-6]. In Australia, it is DWEDL[{  
estimated that by the year 2021, the number of people 0$0 215  
affected by cataract will increase by 63%, due to population ^ cE{Uv  
aging [7]. Surgical intervention is an effective treatment yo(MJ^=d  
for cataract and normal vision (> 20/40) can usually YQyI{  
be restored with intraocular lens (IOL) implantation. ]')y(_{  
Cataract surgery with IOL implantation is currently the fwmXIpteK  
most commonly performed, and is, arguably, the most C]fX=~?bGQ  
cost effective surgical procedure worldwide. Performance 5;G 0$M0  
Published: 20 April 2006 PVIZ Y^64  
BMC Ophthalmology 2006, 6:17 doi:10.1186/1471-2415-6-17 f*A B Im  
Received: 14 December 2005 q/Vl>t  
Accepted: 20 April 2006 +FAxqCkA  
This article is available from: http://www.biomedcentral.com/1471-2415/6/17 {p$@)b  
© 2006 Tan et al; licensee BioMed Central Ltd. sCP|d`'  
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), ,0ilNi>  
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ! 2knS S  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 4[&&E7]EX  
Page 2 of 7 }_F:]lI*R  
(page number not for citation purposes) KeB??1S  
of this surgical procedure has been continuously increasing +IWf~|s  
in the last two decades. Data from the Australian ` AD}6O+x  
Health Insurance Commission has shown a steady wjZ Q.T!  
increase in Medicare claims for cataract surgery [8]. A 2.6- R'6(eA[K  
fold increase in the total number of cataract procedures +> d;%K  
from 1985 to 1994 has been documented in Australia [9]. HG< z,gE 2  
The rate of cataract surgery per thousand persons aged 65 ^TjC  
years or older has doubled in the last 20 years [8,9]. In the = Ezg3$ %-  
Blue Mountains Eye Study population, we observed a onethird U$y wO4.  
increase in cataract surgery prevalence over a mean xf8[&?  
6-year interval, from 6% to nearly 8% in two cross-sectional _~{J."q  
population-based samples with a similar age range w{lj'3z I  
[10]. Further increases in cataract surgery performance 8DMqjt3B  
would be expected as a result of improved surgical skills 8~yP?#p  
and technique, together with extending cataract surgical 08{^Ksg  
benefits to a greater number of older people and an 'Z=_zG/RX  
increased number of persons with surgery performed on jUl_ToX  
both eyes. );y ZyWDV  
Both the prevalence and incidence of age-related cataract Y<kz+d,C  
link directly to the demand for, and the outcome of, cataract {Rb;1 eYj  
surgery and eye health care provision. This report CB,2BTtRE  
aimed to assess temporal changes in the prevalence of cortical oM^vJ3  
and nuclear cataract and posterior subcapsular cataract 3-6MGL9  
(PSC) in two cross-sectional population-based kOdpW  
surveys 6 years apart. &cTOrG  
Methods n[r1h=?j3  
The Blue Mountains Eye Study (BMES) is a populationbased W8u&5#$I  
cohort study of common eye diseases and other /ueOc<[8"  
health outcomes. The study involved eligible permanent @8w5Oudvx  
residents aged 49 years and older, living in two postcode Csp$_uDi  
areas in the Blue Mountains, west of Sydney, Australia. =./PY10'  
Participants were identified through a census and were <HTz  
invited to participate. The study was approved at each 6R8>w,  
stage of the data collection by the Human Ethics Committees W"pHR sf  
of the University of Sydney and the Western Sydney RJd*(!y  
Area Health Service and adhered to the recommendations %C #Ps   
of the Declaration of Helsinki. Written informed consent `F1Yfm jZT  
was obtained from each participant. ~;pP@DA  
Details of the methods used in this study have been hR:i!  
described previously [11]. The baseline examinations $I/ !vV  
(BMES cross-section I) were conducted during 1992– | 2<zYY  
1994 and included 3654 (82.4%) of 4433 eligible residents. ^&y*=6C  
Follow-up examinations (BMES IIA) were conducted hVT>HER  
during 1997–1999, with 2335 (75.0% of BMES ZAeJTCCk  
cross section I survivors) participating. A repeat census of N+5f.c+S-  
the same area was performed in 1999 and identified 1378 N%q{CYF6  
newly eligible residents who moved into the area or the ;"e55|d9I  
eligible age group. During 1999–2000, 1174 (85.2%) of O'^AbO=,  
this group participated in an extension study (BMES IIB). 59:kL<;S-  
BMES cross-section II thus includes BMES IIA (66.5%) LkK[ ,Qj  
and BMES IIB (33.5%) participants (n = 3509). BILZ XMf  
Similar procedures were used for all stages of data collection OEzSItAI/[  
at both surveys. A questionnaire was administered yLnTIE3)  
including demographic, family and medical history. A ;}KJ[5i-V  
detailed eye examination included subjective refraction, RtxAIMzh?  
slit-lamp (Topcon SL-7e camera, Topcon Optical Co, QkTU@T6>o  
Tokyo, Japan) and retroillumination (Neitz CT-R camera, -Gl!W`$I `  
Neitz Instrument Co, Tokyo, Japan) photography of the ;Z;` BGZJ  
lens. Grading of lens photographs in the BMES has been t4~?m{  
previously described [12]. Briefly, masked grading was iWUxB28  
performed on the lens photographs using the Wisconsin :x3DuQP  
Cataract Grading System [13]. Cortical cataract and PSC I{H!K rM!  
were assessed from the retroillumination photographs by Dk")/ ib  
estimating the percentage of the circular grid involved. nSZp,?^  
Cortical cataract was defined when cortical opacity (U.VCSn  
involved at least 5% of the total lens area. PSC was defined 673G6Nk  
when opacity comprised at least 1% of the total lens area. K7(GdKZe  
Slit-lamp photographs were used to assess nuclear cataract u`-:'@4  
using the Wisconsin standard set of four lens photographs KO}TCa  
[13]. Nuclear cataract was defined when nuclear opacity GIR12%-EO  
was at least as great as the standard 4 photograph. Any cataract z|S4\Ae  
was defined to include persons who had previous bOV]!)o  
cataract surgery as well as those with any of three cataract SokU9n!  
types. Inter-grader reliability was high, with weighted '$ G%HUn  
kappa 0.82 for cortical cataract, 0.55 (simple kappa 0.75) OQyZ'  
for nuclear cataract and 0.82 for PSC grading. The intragrader  f|yq~3x)  
reliability for nuclear cataract was assessed with =)Goip  
simple kappa 0.83 for the senior grader who graded j{/wG::  
nuclear cataract at both surveys. All PSC cases were confirmed :ZM=P3QZ  
by an ophthalmologist (PM). 5y~B/.YY  
In cross-section I, 219 persons (6.0%) had missing or B|;?#okx  
ungradable Neitz photographs, leaving 3435 with photographs KDDx[]1Q  
available for cortical cataract and PSC assessment, 8{CBWXo$)  
while 1153 (31.6%) had randomly missing or ungradable oT}Sh4Wt.  
Topcon photographs due to a camera malfunction, leaving %8|?YxiZ:  
2501 with photographs available for nuclear cataract u)P)r,  
assessment. Comparison of characteristics between participants y#lg)nB  
with and without Neitz or Topcon photographs in jSvo-  
cross-section I showed no statistically significant differences 7{f{SIB  
between the two groups, as reported previously @Z9>E+udQ  
[12]. In cross-section II, 441 persons (12.5%) had missing SR9M:%dga  
or ungradable Neitz photographs, leaving 3068 for cortical |c,'0V,"cH  
cataract and PSC assessment, and 648 (18.5%) had (G {2ec:?  
missing or ungradable Topcon photographs, leaving 2860 `SYq/6$VEH  
for nuclear cataract assessment. FzFP 0  
Data analysis was performed using the Statistical Analysis v,c:cKj  
System (SAS, SAS Institute, Cary, NC, USA). Age-adjusted UTuOean ]'  
prevalence was calculated using direct standardization of 0a v2w5>af  
the cross-section II population to the cross-section I population. e= _7Q.cn  
We assessed age-specific prevalence using an y@]:7  
interval of 5 years, so that participants within each age rJcZ a#  
group were independent between the two cross-sectional T7 XbbU   
surveys. x*F_XE1#M  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 AjO|@6  
Page 3 of 7 dv \aP  
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Results ^g N?Io  
Characteristics of the two survey populations have been KHt#mQy)9  
previously compared [14] and showed that age and sex !tv+,l&L  
distributions were similar. Table 1 compares participant |K$EULzz  
characteristics between the two cross-sections. Cross-section 'xc =N  
II participants generally had higher rates of diabetes, gS ^Y?  
hypertension, myopia and more users of inhaled steroids. iJ~e8l0CA  
Cataract prevalence rates in cross-sections I and II are G!m;J8#m(  
shown in Figure 1. The overall prevalence of cortical cataract {DGnh1  
was 23.8% and 23.7% in cross-sections I and II, 5B+I \f&  
respectively (age-sex adjusted P = 0.81). Corresponding -VRKQNT  
prevalence of PSC was 6.3% and 6.0% for the two crosssections ST^{?Q  
(age-sex adjusted P = 0.60). There was an TY *q[AWG  
increased prevalence of nuclear cataract, from 18.7% in G[[<-[C]5  
cross-section I to 23.9% in cross-section II over the 6-year }h`ddo  
period (age-sex adjusted P < 0.001). Prevalence of any cataract 1 gx(L*y,  
(including persons who had cataract surgery), however, q#!c6lG  
was relatively stable (46.9% and 46.8% in crosssections "+KAYsVtU  
I and II, respectively). BvV!?DY4  
After age-standardization, these prevalence rates remained A**PGy.Ni  
stable for cortical cataract (23.8% and 23.5% in the two @) p?!3{"  
surveys) and PSC (6.3% and 5.9%). The slightly increased QDJ:LJz\  
prevalence of nuclear cataract (from 18.7% to 24.2%) was )A a  h  
not altered. AwO'%+Bv  
Table 2 shows the age-specific prevalence rates for cortical 05Go*QvV  
cataract, PSC and nuclear cataract in cross-sections I and K+J fU J  
II. A similar trend of increasing cataract prevalence with #sp8 !8|y  
increasing age was evident for all three types of cataract in xSoXf0zq:  
both surveys. Comparing the age-specific prevalence %oEvp{I  
between the two surveys, a reduction in PSC prevalence in Sk&l8"  
cross-section II was observed in the older age groups (≥ 75 2k3yf_N  
years). In contrast, increased nuclear cataract prevalence `SSUQ#@  
in cross-section II was observed in the older age groups (≥ >n^[-SWJCT  
70 years). Age-specific cortical cataract prevalence was relatively Ks-aJ+}  
consistent between the two surveys, except for a 4 Gm(P~N  
reduction in prevalence observed in the 80–84 age group _ 0Ced&i  
and an increasing prevalence in the older age groups (≥ 85 b5Pakz=jNM  
years). <FFaaGiE>  
Similar gender differences in cataract prevalence were <E.$4 /T  
observed in both surveys (Table 3). Higher prevalence of IB+)2`  
cortical and nuclear cataract in women than men was evident nzK"eNDN.  
but the difference was only significant for cortical tug\X  
cataract (age-adjusted odds ratio, OR, for women 1.3, %/x%hs;d  
95% confidence intervals, CI, 1.1–1.5 in cross-section I ^U4|TR6mub  
and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con- 4C{3>BE  
Table 1: Participant characteristics. oPA [vY  
Characteristics Cross-section I Cross-section II #UpxF?A(  
n % n % /4Lmu+G4  
Age (mean) (66.2) (66.7) ib%x&?||  
50–54 485 13.3 350 10.0 Z*rA~`@K6  
55–59 534 14.6 580 16.5 -'OO6mU  
60–64 638 17.5 600 17.1 )4P5i b  
65–69 671 18.4 639 18.2 zsx12b^w  
70–74 538 14.7 572 16.3 Xqac$%[3  
75–79 422 11.6 407 11.6 nE)|6  
80–84 230 6.3 226 6.4 8/y~3~A{D  
85–89 100 2.7 110 3.1 PNbs7f  
90+ 36 1.0 24 0.7 k5@_8Rc  
Female 2072 56.7 1998 57.0 5E+k}S]M$  
Ever Smokers 1784 51.2 1789 51.2 Pyx$$cj  
Use of inhaled steroids 370 10.94 478 13.8^ 6/#5TdJA  
History of: *ppb 4R;CW  
Diabetes 284 7.8 347 9.9^ \O7?!i  
Hypertension 1669 46.0 1825 52.2^ 2F[;Z*&  
Emmetropia* 1558 42.9 1478 42.2 ,A>i)brc  
Myopia* 442 12.2 495 14.1^ \JLiA>@ @  
Hyperopia* 1633 45.0 1532 43.7 n>dM OQb  
n = number of persons affected >)N}V'9  
* best spherical equivalent refraction correction 79^on8k}  
^ P < 0.01 O;A/(lPW+  
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Page 4 of 7 A*h)p@3t<  
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t L#e|t0'#  
rast, men had slightly higher PSC prevalence than women _e_]$G/TM  
in both cross-sections but the difference was not significant NRKAEf_#w  
(OR 1.1, 95% CI 0.8–1.4 for men in cross-section I Pc]c8~  
and OR 1.2, 95% 0.9–1.6 in cross-section II). Oz9k.[j(  
Discussion RU `TzD  
Findings from two surveys of BMES cross-sectional populations l!ye\  
with similar age and gender distribution showed !qH=l-7A  
that the prevalence of cortical cataract and PSC remained jkNZv. )p  
stable, while the prevalence of nuclear cataract appeared 0zpP$q$  
to have increased. Comparison of age-specific prevalence, T^GdN_qF  
with totally independent samples within each age group, t:M({|m Y  
confirmed the robustness of our findings from the two 7$GP#V1r/  
survey samples. Although lens photographs taken from YKh%`Y1<  
the two surveys were graded for nuclear cataract by the j.C C.[$g  
same graders, who documented a high inter- and intragrader N13 <!QQ  
reliability, we cannot exclude the possibility that !wrl.A/P  
variations in photography, performed by different photographers, v *:m|wl  
may have contributed to the observed difference ==(M vu`  
in nuclear cataract prevalence. However, the overall `T9<}&=!  
Table 2: Age-specific prevalence of cataract types in cross sections I and II. WaMn [/{  
Cataract type Age (years) Cross-section I Cross-section II 9/s- |jD  
n % (95% CL)* n % (95% CL)* 6}ax~wYct  
Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2) `%ymg8^  
55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5) iCx'`^HnP  
60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8) QW2% Gv:  
65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0) "Ln\ZYB]  
70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6) R4qk/@]t  
75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1) 9 J]LV'f7  
80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6) .Yu,&HR  
85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5) WJ9u 3+  
90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2) F37,u|  
PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0) Hh@mIusj  
55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9) 2=3iA09px  
60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6) E_yh9lk  
65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3)  b'Uaj`Sn  
70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3) /r?X33D!  
75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7) fg1 zT~  
80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2) 3> fuH'=  
85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4) Ql V:8:H$  
90+ 23 21.7 (3.5–40.0) 11 0.0 oD}I{&=wa  
Nuclear 50–54 323 1.6 (0.2–2.9) 331 0.9 (–0.2–1.9) 3?}SXmA'@  
55–59 386 2.3 (0.8–3.8) 507 3.6 (1.9–5.2) HxM-VK '  
60–64 453 5.3 (3.2–7.4) 501 11.6 (8.8–14.4) )t.q[O`  
65–69 478 17.2 (13.8–20.1) 534 18.5 (15.2–21.9) $ `ho+  
70–74 392 27.6 (23.1–32.0) 453 36.0 (31.6–40.4) g+CH F?O  
75–79 255 45.1 (39.0–51.3) 302 55.6 (50.0–61.3) 5y~[2jB:  
80–84 146 54.1 (45.9–62.3) 147 73.5 (66.3–80.7) 7:;V[/   
85–89 50 64.0 (50.2–77.8) 70 80.0 (70.4–89.6) N!va12  
90+ 18 72.2 (49.3–95.1) 15 73.3 (48.0–98.7) N,1wfOE  
n = number of persons  +*!!  
* 95% Confidence Limits C/$IF M<  
Cataract FMioguunrtea i1n ps rEeyvea lSetnucdey in cross-sections I and II of the Blue x{- caOH  
Cataract prevalence in cross-sections I and II of the Blue 83 n: h08  
Mountains Eye Study. D'&L wU,o  
0 )>/c/ B  
10 oMVwId f  
20 7MfT~v  
30 y/ FisX  
40 We ->d |=  
50 t&xx-4  
cortical PSC nuclear any ymzm x$o=  
cataract 8%4`Yj=  
Cataract type V#~. Jg7  
% A0XFu}  
Cross-section I 0D'Wr(U(  
Cross-section II J-}NFWR;t  
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Page 5 of 7 ZeeuH"A  
(page number not for citation purposes) Zx_m?C_2_  
prevalence of any cataract (including cataract surgery) was R+K[/AA  
relatively stable over the 6-year period. C gx?K]>y  
Although different population-based studies used different fo.m&mKgo  
grading systems to assess cataract [15], the overall 2]+.8G7D%  
prevalence of the three cataract types were similar across qo@dFKy  
different study populations [12,16-23]. Most studies have Cu:Zn%  
suggested that nuclear cataract is the most prevalent type L,6Y=?  
of cataract, followed by cortical cataract [16-20]. Ours and .6K>"  
other studies reported that cortical cataract was the most e@OA>  
prevalent type [12,21-23]. K\b O[J  
Our age-specific prevalence data show a reduction of +a/o)C{  
15.9% in cortical cataract prevalence for the 80–84 year :j ~5(K"  
age group, concordant with an increase in cataract surgery aJ8pJ{,P  
prevalence by 9% in those aged 80+ years observed in the -Q6pV<i  
same study population [10]. Although cortical cataract is $T6Qg(p  
thought to be the least likely cataract type leading to a cataract spJ(1F{|V  
surgery, this may not be the case in all older persons. Nd!VR+IZ  
A relatively stable cortical cataract and PSC prevalence 6mdnEmFM]  
over the 6-year period is expected. We cannot offer a oui!fTy  
definitive explanation for the increase in nuclear cataract :,m)D775S  
prevalence. A possible explanation could be that a moderate s{e(- 7'  
level of nuclear cataract causes less visual disturbance ozC!q)j  
than the other two types of cataract, thus for the oldest age bSf(DSqx  
groups, persons with nuclear cataract could have been less |8 bO5l:  
likely to have surgery unless it is very dense or co-existing au|^V^m  
with cortical cataract or PSC. Previous studies have shown K;[%S  
that functional vision and reading performance were high f_ztnRw  
in patients undergoing cataract surgery who had nuclear hyiMOa  
cataract only compared to those with mixed type of cataract b`W*vduf  
(nuclear and cortical) or PSC [24,25]. In addition, the P]"d eB|  
overall prevalence of any cataract (including cataract surgery) 5L}>+js2  
was similar in the two cross-sections, which appears jJ!-hg4?]  
to support our speculation that in the oldest age group, {X<4wx eTo  
nuclear cataract may have been less likely to be operated 4q13xX  
than the other two types of cataract. This could have UglG!1L  
resulted in an increased nuclear cataract prevalence (due l&*)r;9  
to less being operated), compensated by the decreased cmhN(==  
prevalence of cortical cataract and PSC (due to these being k%}89glm  
more likely to be operated), leading to stable overall prevalence [!@oRK=~  
of any cataract. *3O>J"  
Possible selection bias arising from selective survival Xexe{h4t_>  
among persons without cataract could have led to underestimation t*d >eK`:N  
of cataract prevalence in both surveys. We Jh4&Qh|t  
assume that such an underestimation occurred equally in ZuvPDW%  
both surveys, and thus should not have influenced our VtO;UN  
assessment of temporal changes. X@qk>/  
Measurement error could also have partially contributed rEyz|k:  
to the observed difference in nuclear cataract prevalence. 1N9< d,  
Assessment of nuclear cataract from photographs is a iv:/g|MBI&  
potentially subjective process that can be influenced by B>Cs&}Y!  
variations in photography (light exposure, focus and the 0[:9 Hb6  
slit-lamp angle when the photograph was taken) and pEVgJ/>  
grading. Although we used the same Topcon slit-lamp $54=gRo^  
camera and the same two graders who graded photos KO"Jg-6r|  
from both surveys, we are still not able to exclude the possibility M6]0Y@@>  
of a partial influence from photographic variation Ji6`-~ k  
on this result. ZSPgci  
A similar gender difference (women having a higher rate pSQCT  
than men) in cortical cataract prevalence was observed in aLKMDiT  
both surveys. Our findings are in keeping with observations _t|G@D{   
from the Beaver Dam Eye Study [18], the Barbados Kr/h`RM  
Eye Study [22] and the Lens Opacities Case-Control ^+.t-3|U  
Group [26]. It has been suggested that the difference SgpZ;\_  
could be related to hormonal factors [18,22]. A previous drENkS=,  
study on biochemical factors and cataract showed that a }2ql?K  
lower level of iron was associated with an increased risk of 9K;k%  
cortical cataract [27]. No interaction between sex and biochemical 19F ;oFp  
factors were detected and no gender difference K lli$40  
was assessed in this study [27]. The gender difference seen aGB0-;.t7  
in cortical cataract could be related to relatively low iron - J"qrpZ^  
levels and low hemoglobin concentration usually seen in dU oWo3r=  
women [28]. Diabetes is a known risk factor for cortical v Zb|!#I  
Table 3: Gender distribution of cataract types in cross-sections I and II. eQU-&-wt0  
Cataract type Gender Cross-section I Cross-section II E3S%s  
n % (95% CL)* n % (95% CL)* 6| *(dE2x(  
Cortical Male 1496 21.1 (19.0–23.1) 1328 20.4 (18.2–22.6) (;0$i?3\  
Female 1939 25.9 (23.9–27.8) 1785 26.2 (24.2–28.3) )o#6-K+b  
PSC Male 1500 6.5 (5.2–7.7) 1314 6.4 (5.1–7.7) @up&q  
Female 1944 6.2 (5.1–7.2) 1753 5.7 (4.6–6.7) ]}z'X!v_@  
Nuclear Male 1106 17.6 (15.4–19.9) 1225 22.5 (20.1–24.8) t_dcV%=  
Female 1395 19.5 (17.4–21.6) 1635 25.0 (22.9–27.1) VK2@2`$  
n = number of persons v:r D3=M-  
* 95% Confidence Limits lSH ZV Fd  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 #^|| ]g/N  
Page 6 of 7 K;oV"KRK  
(page number not for citation purposes) Hf VHI1f  
cataract but in this particular population diabetes is more tm(v~L%$>]  
prevalent in men than women in all age groups [29]. Differential  T/[f5?p  
exposures to cataract risk factors or different dietary 9s! 2 wwh  
or lifestyle patterns between men and women may HSNOL  
also be related to these observations and warrant further 8r,9OM  
study. -=>sTMWpr  
Conclusion bqSMDK  
In summary, in two population-based surveys 6 years 1p8:.1)q  
apart, we have documented a relatively stable prevalence N99[.mErU  
of cortical cataract and PSC over the period. The observed c Zqfz  
overall increased nuclear cataract prevalence by 5% over a ?TDvCL  
6-year period needs confirmation by future studies, and YWEYHr;%^?  
reasons for such an increase deserve further study. 0HqPyM13Q  
Competing interests +A@m9  
The author(s) declare that they have no competing interests. ~i% -WX  
Authors' contributions >tN5vWW  
AGT graded the photographs, performed literature search  KyTuF   
and wrote the first draft of the manuscript. JJW graded the H"eS<eT  
photographs, critically reviewed and modified the manuscript. Uo~T'mA"  
ER performed the statistical analysis and critically u t$c)_  
reviewed the manuscript. PM designed and directed the tZbFvk2  
study, adjudicated cataract cases and critically reviewed <Z},A-\ S*  
and modified the manuscript. All authors read and `?l3Ct*  
approved the final manuscript. c&E]E(  
Acknowledgements p!_[qs  
This study was supported by the Australian National Health & Medical >z(wf>2J  
Research Council, Canberra, Australia (Grant Nos 974159, 991407). The +~N!9eMc  
abstract was presented at the Association for Research in Vision and Ophthalmology vB.l0!c\e_  
(ARVO) meeting in Fort Lauderdale, Florida, USA, May 2005. @Gt`Ds9=  
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