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BMC Ophthalmology

BioMed Central ,?<h] !aQ  
Page 1 of 7 pE/3-0;}N  
(page number not for citation purposes) 7(8  
BMC Ophthalmology 'lsq3!d.  
Research article Open Access aE+$&_>ef  
Comparison of age-specific cataract prevalence in two ?VZXJO{^  
population-based surveys 6 years apart @b*T4hwA.  
Ava Grace Tan†, Jie Jin Wang*†, Elena Rochtchina† and Paul Mitchell† J s<MJ4r>/  
Address: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital, b/,!J] W  
Westmead, NSW, Australia \1`D aQp7  
Email: Ava Grace Tan - ava_tan@wmi.usyd.edu.au; Jie Jin Wang* - jiejin_wang@wmi.usyd.edu.au; _2X6bIE  
Elena Rochtchina - elena_rochtchina@wmi.usyd.edu.au; Paul Mitchell - paul_mitchell@wmi.usyd.edu.au R QS:h]?:l  
* Corresponding author †Equal contributors xDA,?i;T 0  
Abstract $F@L$& ~  
Background: In this study, we aimed to compare age-specific cortical, nuclear and posterior /zG-\eU  
subcapsular (PSC) cataract prevalence in two surveys 6 years apart. S,Wl)\  
Methods: The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in aEFe!_QY  
cross-section I (1992–4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in *fvI.cKiGP  
cross-section II (1997–2000, 66.5% overlap with cross-section I). Cataract was assessed from lens z^!A /a[[!  
photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if snTJe[^d  
cortical opacity comprised ≥ 5% of lens area. Nuclear cataract was defined if nuclear opacity ≥ Fe& n,  
Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons iVpA @p   
who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and V>>) 7E:Q  
0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using WrHgF*[  
an interval of 5 years, so that participants within each age group were independent between the ,LW(mdIe(  
two surveys. ))CXjwLj;  
Results: Age and gender distributions were similar between the two populations. The age-specific +6#%P  
prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The 3vRL g b  
prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization, $ gr6  
the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased {? K|(C  
prevalence of nuclear cataract (18.7%, 24.2%) remained. 7SA-OFM  
Conclusion: In two surveys of two population-based samples with similar age and gender /]k ,,&  
distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period. 6_9:Eb=^v!  
The increased prevalence of nuclear cataract deserves further study. y?Hj %,  
Background C>JekPeM  
Age-related cataract is the leading cause of reversible visual MfNpQ:]c\  
impairment in older persons [1-6]. In Australia, it is EDq$vB  
estimated that by the year 2021, the number of people M\\e e3Ih  
affected by cataract will increase by 63%, due to population eN<>#: `  
aging [7]. Surgical intervention is an effective treatment { .aK{ V  
for cataract and normal vision (> 20/40) can usually Giy3eva2  
be restored with intraocular lens (IOL) implantation. NK  
Cataract surgery with IOL implantation is currently the #RR:3ZP ZC  
most commonly performed, and is, arguably, the most e'k;A{Oh  
cost effective surgical procedure worldwide. Performance {2}tPT[a(  
Published: 20 April 2006 Wz6]*P`qv  
BMC Ophthalmology 2006, 6:17 doi:10.1186/1471-2415-6-17 >G-8FL  
Received: 14 December 2005 cS"f  
Accepted: 20 April 2006 2X qTyf<  
This article is available from: http://www.biomedcentral.com/1471-2415/6/17 3iu!6lC  
© 2006 Tan et al; licensee BioMed Central Ltd. 3o+KP[A  
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), _L&n &y1+%  
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Ph(]?MG\_  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 m!HC-[<  
Page 2 of 7 _-4n ~(  
(page number not for citation purposes) c[(yU#@  
of this surgical procedure has been continuously increasing h|J;6Sm@  
in the last two decades. Data from the Australian mV6#!_"  
Health Insurance Commission has shown a steady ?ada>"~GR_  
increase in Medicare claims for cataract surgery [8]. A 2.6- >|l;*Kw,/P  
fold increase in the total number of cataract procedures KotP V  
from 1985 to 1994 has been documented in Australia [9]. 2-B6IPeI  
The rate of cataract surgery per thousand persons aged 65 5Z* b( R  
years or older has doubled in the last 20 years [8,9]. In the \w{@u)h  
Blue Mountains Eye Study population, we observed a onethird pp/#Am  
increase in cataract surgery prevalence over a mean ^dFh g_GhF  
6-year interval, from 6% to nearly 8% in two cross-sectional x7vq?fP0n  
population-based samples with a similar age range w@87]/4Rq  
[10]. Further increases in cataract surgery performance CkRyzF  
would be expected as a result of improved surgical skills =hJfL}&O3  
and technique, together with extending cataract surgical y:qx5Mi  
benefits to a greater number of older people and an VMaS;)0f@  
increased number of persons with surgery performed on pNP_f:A|  
both eyes. Kp8fh-4_  
Both the prevalence and incidence of age-related cataract 6hp{,8|D"m  
link directly to the demand for, and the outcome of, cataract <#zwKTmK1  
surgery and eye health care provision. This report -UJ?L  
aimed to assess temporal changes in the prevalence of cortical k69kv9v@J  
and nuclear cataract and posterior subcapsular cataract I"B8_  
(PSC) in two cross-sectional population-based * nLIXnm  
surveys 6 years apart. 6*sw,sU[y  
Methods t @;WgIp(&  
The Blue Mountains Eye Study (BMES) is a populationbased oL#xDG  
cohort study of common eye diseases and other j H(&oV  
health outcomes. The study involved eligible permanent "t=UX -3  
residents aged 49 years and older, living in two postcode [$^A@bqk  
areas in the Blue Mountains, west of Sydney, Australia. 6nc0=~='$  
Participants were identified through a census and were  O)OUy  
invited to participate. The study was approved at each vmvFBzLR  
stage of the data collection by the Human Ethics Committees V`by*s  
of the University of Sydney and the Western Sydney NIaF5z  
Area Health Service and adhered to the recommendations TMqY4;UeL  
of the Declaration of Helsinki. Written informed consent t=Jm|wJnUA  
was obtained from each participant. :\ mRtVH   
Details of the methods used in this study have been G)8ChnJa!m  
described previously [11]. The baseline examinations .A(i=!{q  
(BMES cross-section I) were conducted during 1992– e{0L%%2K  
1994 and included 3654 (82.4%) of 4433 eligible residents. c yP,[?N  
Follow-up examinations (BMES IIA) were conducted ck$M(^)l  
during 1997–1999, with 2335 (75.0% of BMES h8jB=e, H  
cross section I survivors) participating. A repeat census of W^k,Pmopy  
the same area was performed in 1999 and identified 1378 ;%W dvnW  
newly eligible residents who moved into the area or the (i]Z|@|)  
eligible age group. During 1999–2000, 1174 (85.2%) of v,jhE9_O0  
this group participated in an extension study (BMES IIB). Oc~aW3*A(  
BMES cross-section II thus includes BMES IIA (66.5%) 3fp> 4;ym'  
and BMES IIB (33.5%) participants (n = 3509). \2 >?6zs  
Similar procedures were used for all stages of data collection I+",b4  
at both surveys. A questionnaire was administered OJpj}R  
including demographic, family and medical history. A ;& |qSa'  
detailed eye examination included subjective refraction, gu<V (M\  
slit-lamp (Topcon SL-7e camera, Topcon Optical Co, [7.agI@=  
Tokyo, Japan) and retroillumination (Neitz CT-R camera, H\#:,s{1  
Neitz Instrument Co, Tokyo, Japan) photography of the ){ gAj  
lens. Grading of lens photographs in the BMES has been XYAm J   
previously described [12]. Briefly, masked grading was m$:&P|!'p  
performed on the lens photographs using the Wisconsin {/|qjkT&W  
Cataract Grading System [13]. Cortical cataract and PSC r~>,$[|n})  
were assessed from the retroillumination photographs by QDE$ E.a  
estimating the percentage of the circular grid involved. 5I' d PNf  
Cortical cataract was defined when cortical opacity ^npJUa  
involved at least 5% of the total lens area. PSC was defined m@\ZHbq  
when opacity comprised at least 1% of the total lens area. 2|{V,!/cvG  
Slit-lamp photographs were used to assess nuclear cataract `@XehSQ  
using the Wisconsin standard set of four lens photographs .Dw,"VHP  
[13]. Nuclear cataract was defined when nuclear opacity 8\Hr5FqB(  
was at least as great as the standard 4 photograph. Any cataract -JV~[-,  
was defined to include persons who had previous J/W{/E>;  
cataract surgery as well as those with any of three cataract LFu%v7L`  
types. Inter-grader reliability was high, with weighted k;Fh4Hv  
kappa 0.82 for cortical cataract, 0.55 (simple kappa 0.75) .C bGDZ  
for nuclear cataract and 0.82 for PSC grading. The intragrader I1"MPx{  
reliability for nuclear cataract was assessed with CxF-Z7 '  
simple kappa 0.83 for the senior grader who graded ,pt%) c  
nuclear cataract at both surveys. All PSC cases were confirmed %b}gDWs  
by an ophthalmologist (PM). IL!=mZ>2O  
In cross-section I, 219 persons (6.0%) had missing or <@uOCRb V  
ungradable Neitz photographs, leaving 3435 with photographs 23ze/;6%A  
available for cortical cataract and PSC assessment, #"f' 7'TE  
while 1153 (31.6%) had randomly missing or ungradable q/gB<p9  
Topcon photographs due to a camera malfunction, leaving uTvv(f  
2501 with photographs available for nuclear cataract "!UVs+)]  
assessment. Comparison of characteristics between participants >-)h|w i  
with and without Neitz or Topcon photographs in pa<qZZ  
cross-section I showed no statistically significant differences W/+K9S25  
between the two groups, as reported previously U 4,2br >  
[12]. In cross-section II, 441 persons (12.5%) had missing D'[Uc6  
or ungradable Neitz photographs, leaving 3068 for cortical :@3Wg3N  
cataract and PSC assessment, and 648 (18.5%) had 53OJ-m%a  
missing or ungradable Topcon photographs, leaving 2860 #-# NqX:  
for nuclear cataract assessment. d/,E2i{I7  
Data analysis was performed using the Statistical Analysis 8cWZ"v  
System (SAS, SAS Institute, Cary, NC, USA). Age-adjusted bKbp?-]  
prevalence was calculated using direct standardization of cu7(.  
the cross-section II population to the cross-section I population. <,1 fkq>,  
We assessed age-specific prevalence using an F?4(5 K  
interval of 5 years, so that participants within each age ; y.E!  
group were independent between the two cross-sectional x4K`]Fvhl  
surveys. S"2qJ!.u  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 ]$iN#d|ZU  
Page 3 of 7 LXfCmc9|Z  
(page number not for citation purposes) ~oD8Rnf  
Results ` $5UHa2/  
Characteristics of the two survey populations have been G*8GGWB^a  
previously compared [14] and showed that age and sex 8g/F)~s^F  
distributions were similar. Table 1 compares participant gUax'^w;V;  
characteristics between the two cross-sections. Cross-section /Wj,1WX~  
II participants generally had higher rates of diabetes, X]*QUV]i  
hypertension, myopia and more users of inhaled steroids. j|_E$L A\  
Cataract prevalence rates in cross-sections I and II are %}Q&1P=  
shown in Figure 1. The overall prevalence of cortical cataract ) M<vAUF  
was 23.8% and 23.7% in cross-sections I and II, x K%=  
respectively (age-sex adjusted P = 0.81). Corresponding JWO=!^  
prevalence of PSC was 6.3% and 6.0% for the two crosssections p9ZXbAJ{  
(age-sex adjusted P = 0.60). There was an =!MY4&YX  
increased prevalence of nuclear cataract, from 18.7% in '?*g%Yuz  
cross-section I to 23.9% in cross-section II over the 6-year )9nElb2  
period (age-sex adjusted P < 0.001). Prevalence of any cataract U yqXMbw@  
(including persons who had cataract surgery), however, !b|'Vp^U  
was relatively stable (46.9% and 46.8% in crosssections jFG0`n}I  
I and II, respectively). f^Bc  
After age-standardization, these prevalence rates remained ZXb0Y2AVx  
stable for cortical cataract (23.8% and 23.5% in the two GR4?BuY,  
surveys) and PSC (6.3% and 5.9%). The slightly increased "dh:-x6  
prevalence of nuclear cataract (from 18.7% to 24.2%) was Jc*XX u)  
not altered. D$ e B ,~  
Table 2 shows the age-specific prevalence rates for cortical 4jm K].  
cataract, PSC and nuclear cataract in cross-sections I and TW&DFKK`  
II. A similar trend of increasing cataract prevalence with #&!G"x7  
increasing age was evident for all three types of cataract in "i)Yvh[y  
both surveys. Comparing the age-specific prevalence !UBO_X%dz  
between the two surveys, a reduction in PSC prevalence in sYbH|}  
cross-section II was observed in the older age groups (≥ 75 FcbM7/  
years). In contrast, increased nuclear cataract prevalence Bn wzcl  
in cross-section II was observed in the older age groups (≥ Xo5$X7m  
70 years). Age-specific cortical cataract prevalence was relatively <|6%9@  
consistent between the two surveys, except for a   NY  
reduction in prevalence observed in the 80–84 age group 5rxA<G s  
and an increasing prevalence in the older age groups (≥ 85 N"5fmY<  
years). P1kB>" bR  
Similar gender differences in cataract prevalence were IfdI|ya  
observed in both surveys (Table 3). Higher prevalence of dXvt6kF  
cortical and nuclear cataract in women than men was evident Q'NmSX)0  
but the difference was only significant for cortical .=R lOK  
cataract (age-adjusted odds ratio, OR, for women 1.3, t={0(  
95% confidence intervals, CI, 1.1–1.5 in cross-section I {[G`Z9]z&-  
and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con- @M;(K<%h  
Table 1: Participant characteristics. '"YYj$> '  
Characteristics Cross-section I Cross-section II nL `9l1  
n % n % D9ufoa&ua  
Age (mean) (66.2) (66.7) BR_TykP  
50–54 485 13.3 350 10.0 )$M,Ul  
55–59 534 14.6 580 16.5 nS.G~c|  
60–64 638 17.5 600 17.1 #*$p-I=  
65–69 671 18.4 639 18.2 n@>wwp  
70–74 538 14.7 572 16.3 A*]$v  
75–79 422 11.6 407 11.6 C".1 +Um  
80–84 230 6.3 226 6.4 Ww9;UP'G  
85–89 100 2.7 110 3.1 xF8S*,#,*  
90+ 36 1.0 24 0.7 NP t(MFK \  
Female 2072 56.7 1998 57.0 H[&@}v,L  
Ever Smokers 1784 51.2 1789 51.2 Cn h|D^{s  
Use of inhaled steroids 370 10.94 478 13.8^ Epjff@ 7A  
History of: Lk, +Tfk"  
Diabetes 284 7.8 347 9.9^ ]r"Yqv3  
Hypertension 1669 46.0 1825 52.2^ H#(<-)j0_  
Emmetropia* 1558 42.9 1478 42.2 QApyP CH  
Myopia* 442 12.2 495 14.1^ .XH8YT42  
Hyperopia* 1633 45.0 1532 43.7 !k&)EWP?  
n = number of persons affected Yv\!vW7I  
* best spherical equivalent refraction correction x7ATI[b[  
^ P < 0.01 aC\4}i<  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 3:`XG2'  
Page 4 of 7 !D:k!  
(page number not for citation purposes) o0Gx%99'  
t mnQ'X-q3iO  
rast, men had slightly higher PSC prevalence than women 9M2f!kJP$  
in both cross-sections but the difference was not significant h_ ZX/k  
(OR 1.1, 95% CI 0.8–1.4 for men in cross-section I sBjXE>_#)  
and OR 1.2, 95% 0.9–1.6 in cross-section II). 4XG]z_+I  
Discussion Jt=>-Spj  
Findings from two surveys of BMES cross-sectional populations TmP8 q  
with similar age and gender distribution showed gxM[V>[  
that the prevalence of cortical cataract and PSC remained n`<S&KP|  
stable, while the prevalence of nuclear cataract appeared xqWj|jA  
to have increased. Comparison of age-specific prevalence, V5s& hZZYa  
with totally independent samples within each age group, D rS?=C@  
confirmed the robustness of our findings from the two l>Av5g)  
survey samples. Although lens photographs taken from FAtWsk*pgY  
the two surveys were graded for nuclear cataract by the DTy/jaK  
same graders, who documented a high inter- and intragrader F 6&P~H  
reliability, we cannot exclude the possibility that Xp^$ E6YFy  
variations in photography, performed by different photographers, 2oB?Dn  
may have contributed to the observed difference 6ZgNHARS  
in nuclear cataract prevalence. However, the overall G"Pj6QUva  
Table 2: Age-specific prevalence of cataract types in cross sections I and II. $rB!Ex{@ac  
Cataract type Age (years) Cross-section I Cross-section II LUul7y'"  
n % (95% CL)* n % (95% CL)* %8<2>  
Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2) RAOKZ~`  
55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5) enPYj.*/0  
60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8) J/[7d?hI/  
65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0) l#ygb|=x  
70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6) +gNX7xuY  
75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1) P2QRvn6v  
80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6) H<z30r/-w  
85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5) ' tSnH&c  
90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2) vVdxi9yk  
PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0) |is 9  
55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9) l3\9S#3-^  
60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6) *NF&Y  
65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3) (I!1sE!?1  
70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3) \`&xprqAw  
75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7) Ga?UHw~  
80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2) 1 3\Sh  
85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4) uzO {{S-  
90+ 23 21.7 (3.5–40.0) 11 0.0 k|fh\F+$  
Nuclear 50–54 323 1.6 (0.2–2.9) 331 0.9 (–0.2–1.9) VAt>ji7c  
55–59 386 2.3 (0.8–3.8) 507 3.6 (1.9–5.2) i(z+a6^@|  
60–64 453 5.3 (3.2–7.4) 501 11.6 (8.8–14.4) '%:5axg?]  
65–69 478 17.2 (13.8–20.1) 534 18.5 (15.2–21.9) 9M;I$_U`vj  
70–74 392 27.6 (23.1–32.0) 453 36.0 (31.6–40.4) )v};C<  
75–79 255 45.1 (39.0–51.3) 302 55.6 (50.0–61.3) C\J@fpH(t`  
80–84 146 54.1 (45.9–62.3) 147 73.5 (66.3–80.7) svF*@(- P#  
85–89 50 64.0 (50.2–77.8) 70 80.0 (70.4–89.6) ;+r0 O0;9  
90+ 18 72.2 (49.3–95.1) 15 73.3 (48.0–98.7) "3v7gtGG  
n = number of persons Hc>([?P%t  
* 95% Confidence Limits rT o%=0P  
Cataract FMioguunrtea i1n ps rEeyvea lSetnucdey in cross-sections I and II of the Blue YBR)s\*  
Cataract prevalence in cross-sections I and II of the Blue _AVy:~/  
Mountains Eye Study. uAChu]  
0 ZjE~W>pkQ  
10 YHJ'  
20 Mp!2`4rD  
30 O^y$8OKEi,  
40 }'%$7vL`Ft  
50 CzK%x?~]  
cortical PSC nuclear any (69kvA&|q  
cataract x/pC%25  
Cataract type hU |LFjc  
% )kFme= ;  
Cross-section I 0m qS A  
Cross-section II rD_Ss.\^g  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 .0 rJIO  
Page 5 of 7 fN~8L}!l  
(page number not for citation purposes) Z?vY3)  
prevalence of any cataract (including cataract surgery) was }S Y`KoC1  
relatively stable over the 6-year period. L2:oZ&:u`J  
Although different population-based studies used different NHst7$Y<  
grading systems to assess cataract [15], the overall Yk(NZ3O  
prevalence of the three cataract types were similar across \UV T_=Y  
different study populations [12,16-23]. Most studies have : /n ?4K^  
suggested that nuclear cataract is the most prevalent type A0'tCq]?0  
of cataract, followed by cortical cataract [16-20]. Ours and ,Gf+ U7'K  
other studies reported that cortical cataract was the most &1\u#LU  
prevalent type [12,21-23]. F>hVrUD8  
Our age-specific prevalence data show a reduction of Ktj(&/~}  
15.9% in cortical cataract prevalence for the 80–84 year 1KfJl S+  
age group, concordant with an increase in cataract surgery i[V,IP +  
prevalence by 9% in those aged 80+ years observed in the Ip1QVND  
same study population [10]. Although cortical cataract is :Map,]]B_  
thought to be the least likely cataract type leading to a cataract iX&Z  
surgery, this may not be the case in all older persons. 6PVlZ  
A relatively stable cortical cataract and PSC prevalence nJnO/~|  
over the 6-year period is expected. We cannot offer a J\,@Bm|1n{  
definitive explanation for the increase in nuclear cataract >QbI)if`1  
prevalence. A possible explanation could be that a moderate -0[>}!l=G  
level of nuclear cataract causes less visual disturbance [xH2n\7  
than the other two types of cataract, thus for the oldest age 4.$hHFqS^5  
groups, persons with nuclear cataract could have been less iyHp$~,q?t  
likely to have surgery unless it is very dense or co-existing QQ2OZy> W  
with cortical cataract or PSC. Previous studies have shown @idp8J [td  
that functional vision and reading performance were high 8DmX4*  
in patients undergoing cataract surgery who had nuclear 7i%P&oB  
cataract only compared to those with mixed type of cataract )Q N=>J  
(nuclear and cortical) or PSC [24,25]. In addition, the }sm56}_  
overall prevalence of any cataract (including cataract surgery) `^@g2c+d  
was similar in the two cross-sections, which appears G=0}IPfp  
to support our speculation that in the oldest age group, wHDF TIDI  
nuclear cataract may have been less likely to be operated mSqk[ Ig\  
than the other two types of cataract. This could have S -mzxj  
resulted in an increased nuclear cataract prevalence (due n$Oky-P"  
to less being operated), compensated by the decreased m/"=5*pA  
prevalence of cortical cataract and PSC (due to these being 'FvhzGn9Q  
more likely to be operated), leading to stable overall prevalence %d~9at6-B  
of any cataract. 4h0jX 9  
Possible selection bias arising from selective survival qhHRR/p  
among persons without cataract could have led to underestimation Toa#>Z*+Rb  
of cataract prevalence in both surveys. We H;"N|pBy  
assume that such an underestimation occurred equally in -n$rKEC4  
both surveys, and thus should not have influenced our M,dzf  
assessment of temporal changes. "$w Pq@  
Measurement error could also have partially contributed R,b O{2O  
to the observed difference in nuclear cataract prevalence. ]idD&5gd  
Assessment of nuclear cataract from photographs is a @XSu?+s)  
potentially subjective process that can be influenced by ^_"q`71Dk  
variations in photography (light exposure, focus and the cbHn\m)J,  
slit-lamp angle when the photograph was taken) and %A Du[M.  
grading. Although we used the same Topcon slit-lamp 3Tte8]0  
camera and the same two graders who graded photos %l$&_xV-  
from both surveys, we are still not able to exclude the possibility ]> "/<"  
of a partial influence from photographic variation ;ZW}47:BS6  
on this result. $5 p'+bE  
A similar gender difference (women having a higher rate @nW(KF  
than men) in cortical cataract prevalence was observed in uL{~(?U$  
both surveys. Our findings are in keeping with observations 1RO gUJ;  
from the Beaver Dam Eye Study [18], the Barbados ^T J   
Eye Study [22] and the Lens Opacities Case-Control *'S%gR=Aa+  
Group [26]. It has been suggested that the difference x@R A1&c  
could be related to hormonal factors [18,22]. A previous oL/^[TXjH  
study on biochemical factors and cataract showed that a X;a{JjN  
lower level of iron was associated with an increased risk of Kgio}y  
cortical cataract [27]. No interaction between sex and biochemical ~ m=%a  
factors were detected and no gender difference &!EYT0=>p  
was assessed in this study [27]. The gender difference seen pD.@&J~  
in cortical cataract could be related to relatively low iron NqfDY  
levels and low hemoglobin concentration usually seen in u z2s-,  
women [28]. Diabetes is a known risk factor for cortical uT loj .  
Table 3: Gender distribution of cataract types in cross-sections I and II. U[ungvU1U  
Cataract type Gender Cross-section I Cross-section II Y>m= cqR  
n % (95% CL)* n % (95% CL)* L/+J|_J)  
Cortical Male 1496 21.1 (19.0–23.1) 1328 20.4 (18.2–22.6) %H~gN9Vn#@  
Female 1939 25.9 (23.9–27.8) 1785 26.2 (24.2–28.3) PKs%-Uk  
PSC Male 1500 6.5 (5.2–7.7) 1314 6.4 (5.1–7.7) YD.^\E4o  
Female 1944 6.2 (5.1–7.2) 1753 5.7 (4.6–6.7) bHT@]`@@  
Nuclear Male 1106 17.6 (15.4–19.9) 1225 22.5 (20.1–24.8) ~0{Kga  
Female 1395 19.5 (17.4–21.6) 1635 25.0 (22.9–27.1) T@WMT,J6j  
n = number of persons WQC6{^/4[1  
* 95% Confidence Limits 0-~x[\>>  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 >RnMzH/9  
Page 6 of 7 TRok4uc  
(page number not for citation purposes) vaZZzv{H  
cataract but in this particular population diabetes is more i */U.'#  
prevalent in men than women in all age groups [29]. Differential 9o'6es..@Z  
exposures to cataract risk factors or different dietary q,&T$Tw  
or lifestyle patterns between men and women may kw}1CXD  
also be related to these observations and warrant further 5hK\YTU  
study. GK%ovK  
Conclusion .u?$h0u5  
In summary, in two population-based surveys 6 years e;[8 GE.   
apart, we have documented a relatively stable prevalence Y\|J1I,Z4  
of cortical cataract and PSC over the period. The observed OFbg]{ub?  
overall increased nuclear cataract prevalence by 5% over a [![ (h %  
6-year period needs confirmation by future studies, and .p}Kl$K]  
reasons for such an increase deserve further study. T+D]bfjr&&  
Competing interests =1[g`b  
The author(s) declare that they have no competing interests. BAHx7x#(  
Authors' contributions c `; LF'!  
AGT graded the photographs, performed literature search w5jZI|  
and wrote the first draft of the manuscript. JJW graded the ;)a9Y?  
photographs, critically reviewed and modified the manuscript.  O+j:L  
ER performed the statistical analysis and critically H\bIO!vb  
reviewed the manuscript. PM designed and directed the wm71,R1  
study, adjudicated cataract cases and critically reviewed 3Q)>gh*  
and modified the manuscript. All authors read and 6Qu*'  
approved the final manuscript. RY< b]|  
Acknowledgements 18`%WUPnT  
This study was supported by the Australian National Health & Medical w%n]~w=8  
Research Council, Canberra, Australia (Grant Nos 974159, 991407). The -+_&#twU  
abstract was presented at the Association for Research in Vision and Ophthalmology UV.9 KcN.  
(ARVO) meeting in Fort Lauderdale, Florida, USA, May 2005. nDy=ZsK  
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