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BMC Ophthalmology

BioMed Central jGM+  
Page 1 of 7 lkj^<%N"r  
(page number not for citation purposes) aD2+9?m  
BMC Ophthalmology aWp9K+4R$/  
Research article Open Access ! 11x&Db  
Comparison of age-specific cataract prevalence in two 6SYQRK  
population-based surveys 6 years apart /(`B;?  
Ava Grace Tan†, Jie Jin Wang*†, Elena Rochtchina† and Paul Mitchell† 5& &6e`  
Address: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital, ] D(laqS;"  
Westmead, NSW, Australia 1 \#n{a3  
Email: Ava Grace Tan - ava_tan@wmi.usyd.edu.au; Jie Jin Wang* - jiejin_wang@wmi.usyd.edu.au; >a5M:s)  
Elena Rochtchina - elena_rochtchina@wmi.usyd.edu.au; Paul Mitchell - paul_mitchell@wmi.usyd.edu.au Gi<ik~  
* Corresponding author †Equal contributors S6.N)7y  
Abstract kR C0iTV'I  
Background: In this study, we aimed to compare age-specific cortical, nuclear and posterior /+FZDRf!r  
subcapsular (PSC) cataract prevalence in two surveys 6 years apart. ?*I _'2  
Methods: The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in U}c[oA  
cross-section I (1992–4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in lX)RG*FlTC  
cross-section II (1997–2000, 66.5% overlap with cross-section I). Cataract was assessed from lens p1dqDgF*  
photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if G4!$48  
cortical opacity comprised ≥ 5% of lens area. Nuclear cataract was defined if nuclear opacity ≥ ^1&xt(G  
Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons P,S$qD*4  
who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and w|6;Pf~1y)  
0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using 69Y>iPRU  
an interval of 5 years, so that participants within each age group were independent between the "HWl7c3q  
two surveys. ;pU#3e+P8  
Results: Age and gender distributions were similar between the two populations. The age-specific ]jWe']T  
prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The `r; .  
prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization, Z%*_kk  
the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased Dh*>361y-  
prevalence of nuclear cataract (18.7%, 24.2%) remained. nwd 02tu  
Conclusion: In two surveys of two population-based samples with similar age and gender LK8K=AA3P  
distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period. %@<}z|.4  
The increased prevalence of nuclear cataract deserves further study. MC5M><5\  
Background e+"r L]  
Age-related cataract is the leading cause of reversible visual v})0zz?,1  
impairment in older persons [1-6]. In Australia, it is >@b7 0X!J]  
estimated that by the year 2021, the number of people )J/,-p  
affected by cataract will increase by 63%, due to population ArBgg[i  
aging [7]. Surgical intervention is an effective treatment IX eb6j8  
for cataract and normal vision (> 20/40) can usually l?_Iu_Qp  
be restored with intraocular lens (IOL) implantation. )j6VROt  
Cataract surgery with IOL implantation is currently the V@jR8zv|_  
most commonly performed, and is, arguably, the most `0+zF-  
cost effective surgical procedure worldwide. Performance %g3@m5&  
Published: 20 April 2006 B7qm;(?X&  
BMC Ophthalmology 2006, 6:17 doi:10.1186/1471-2415-6-17 /}?"O~5M"  
Received: 14 December 2005 E K ks8  
Accepted: 20 April 2006 XW6>;:4k  
This article is available from: http://www.biomedcentral.com/1471-2415/6/17 sygAEL;.  
© 2006 Tan et al; licensee BioMed Central Ltd.  WpX)[au  
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), l -~H Y*  
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. }E$^!q{  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 ' }rUbJo  
Page 2 of 7 k<uC[)_  
(page number not for citation purposes) tk4~ 8  
of this surgical procedure has been continuously increasing >\hu1C|W  
in the last two decades. Data from the Australian n~ \"W  
Health Insurance Commission has shown a steady sHO6y0P  
increase in Medicare claims for cataract surgery [8]. A 2.6- #_{3W-35*  
fold increase in the total number of cataract procedures f.0~HnNg1  
from 1985 to 1994 has been documented in Australia [9]. vj<HthC.k  
The rate of cataract surgery per thousand persons aged 65 m4(:H(Za  
years or older has doubled in the last 20 years [8,9]. In the O3#4B!J$E  
Blue Mountains Eye Study population, we observed a onethird -~eNC^t;W  
increase in cataract surgery prevalence over a mean Kx?3]  
6-year interval, from 6% to nearly 8% in two cross-sectional l)`bm/k]V  
population-based samples with a similar age range k}y1I W+3  
[10]. Further increases in cataract surgery performance $6 \v1  
would be expected as a result of improved surgical skills 9mkt.>$  
and technique, together with extending cataract surgical 2S EfEkk  
benefits to a greater number of older people and an \?&P|7N  
increased number of persons with surgery performed on  q%,q"WU  
both eyes. vMKmHq  
Both the prevalence and incidence of age-related cataract 6rMGl zuRo  
link directly to the demand for, and the outcome of, cataract @#Jc!p7)  
surgery and eye health care provision. This report V*SKWP  
aimed to assess temporal changes in the prevalence of cortical Z8tQ#Pu{  
and nuclear cataract and posterior subcapsular cataract #R<4K0Xan  
(PSC) in two cross-sectional population-based J3cbDE%^m  
surveys 6 years apart. U'@eUY(Ov$  
Methods vK)^;T ;  
The Blue Mountains Eye Study (BMES) is a populationbased qQ[&FjTO`  
cohort study of common eye diseases and other si,fs%D&  
health outcomes. The study involved eligible permanent +[Nc";Oy  
residents aged 49 years and older, living in two postcode }5-^:}gL   
areas in the Blue Mountains, west of Sydney, Australia. K5No6dsD  
Participants were identified through a census and were B ?96d'A  
invited to participate. The study was approved at each |H 0+.f;  
stage of the data collection by the Human Ethics Committees 6"C$]kF?  
of the University of Sydney and the Western Sydney c*$&MCh  
Area Health Service and adhered to the recommendations Z?|\0GR+`5  
of the Declaration of Helsinki. Written informed consent 1a 4 [w  
was obtained from each participant. U`sybtuBP'  
Details of the methods used in this study have been p6u"$)wt  
described previously [11]. The baseline examinations 8xzEbRNJ)  
(BMES cross-section I) were conducted during 1992– _svY.p s*  
1994 and included 3654 (82.4%) of 4433 eligible residents. y)o!F^  
Follow-up examinations (BMES IIA) were conducted O?|opD  
during 1997–1999, with 2335 (75.0% of BMES X>l  
cross section I survivors) participating. A repeat census of ?kvkkycI   
the same area was performed in 1999 and identified 1378 \xJT sdd  
newly eligible residents who moved into the area or the ';4DU h p  
eligible age group. During 1999–2000, 1174 (85.2%) of rld4uy}m  
this group participated in an extension study (BMES IIB). T ) T0.c  
BMES cross-section II thus includes BMES IIA (66.5%) } <; y,4f  
and BMES IIB (33.5%) participants (n = 3509). +ew2+2  
Similar procedures were used for all stages of data collection 9Y&,dBj+  
at both surveys. A questionnaire was administered pn?c6K vO  
including demographic, family and medical history. A $[txZN  
detailed eye examination included subjective refraction, :c%vl$  
slit-lamp (Topcon SL-7e camera, Topcon Optical Co, e. 9oB<Etp  
Tokyo, Japan) and retroillumination (Neitz CT-R camera, %tiFx:F+  
Neitz Instrument Co, Tokyo, Japan) photography of the u|h>z|4lJj  
lens. Grading of lens photographs in the BMES has been d4<Ic#  
previously described [12]. Briefly, masked grading was R06q~ >  
performed on the lens photographs using the Wisconsin | W:JI  
Cataract Grading System [13]. Cortical cataract and PSC 6?OH"!b2-}  
were assessed from the retroillumination photographs by w. exLC  
estimating the percentage of the circular grid involved.  L>Bf}^  
Cortical cataract was defined when cortical opacity 7Fb |~In<Z  
involved at least 5% of the total lens area. PSC was defined >Z ZX]#=I  
when opacity comprised at least 1% of the total lens area. JK0L&t<  
Slit-lamp photographs were used to assess nuclear cataract "2:]9j  
using the Wisconsin standard set of four lens photographs &z;F'>"  
[13]. Nuclear cataract was defined when nuclear opacity bJ8G5QU  
was at least as great as the standard 4 photograph. Any cataract 44_ 7gOZ  
was defined to include persons who had previous A7@5lHMF  
cataract surgery as well as those with any of three cataract <EKDP>,~  
types. Inter-grader reliability was high, with weighted p\5DW'  
kappa 0.82 for cortical cataract, 0.55 (simple kappa 0.75) ZVu&q{s,  
for nuclear cataract and 0.82 for PSC grading. The intragrader j2NnDz'  
reliability for nuclear cataract was assessed with w8i"-SE  
simple kappa 0.83 for the senior grader who graded gHc0n0ZV  
nuclear cataract at both surveys. All PSC cases were confirmed FaO=<jYi  
by an ophthalmologist (PM). ;\yY*  
In cross-section I, 219 persons (6.0%) had missing or Z!o&};_j  
ungradable Neitz photographs, leaving 3435 with photographs z;`o>Ja2  
available for cortical cataract and PSC assessment, yAO Ye"d  
while 1153 (31.6%) had randomly missing or ungradable F/;uN5{o  
Topcon photographs due to a camera malfunction, leaving 9qxB/5d_  
2501 with photographs available for nuclear cataract 3uA%1 E  
assessment. Comparison of characteristics between participants  b oAu  
with and without Neitz or Topcon photographs in xKIzEN &  
cross-section I showed no statistically significant differences C8i6ESmU  
between the two groups, as reported previously =9@{U2 =l  
[12]. In cross-section II, 441 persons (12.5%) had missing tM3eB= .*  
or ungradable Neitz photographs, leaving 3068 for cortical t~m >\(&  
cataract and PSC assessment, and 648 (18.5%) had 3>%oGbo  
missing or ungradable Topcon photographs, leaving 2860 Iqe=)   
for nuclear cataract assessment. lrg3n[y-l  
Data analysis was performed using the Statistical Analysis m":lKXpQ  
System (SAS, SAS Institute, Cary, NC, USA). Age-adjusted *|S.[i_7  
prevalence was calculated using direct standardization of ./nq*4=  
the cross-section II population to the cross-section I population. WO{V,<;  
We assessed age-specific prevalence using an K4938 v  
interval of 5 years, so that participants within each age tVJ}NI #  
group were independent between the two cross-sectional 2 t'^  
surveys. mD @#,B7A  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 kGbtZ} W  
Page 3 of 7 a?#v,4t^  
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Results R zG7Xr=t  
Characteristics of the two survey populations have been YU! SdT$  
previously compared [14] and showed that age and sex 3 D<s #  
distributions were similar. Table 1 compares participant Z6@W)QX  
characteristics between the two cross-sections. Cross-section 9 -7.4!]I  
II participants generally had higher rates of diabetes, m]t`;lr<  
hypertension, myopia and more users of inhaled steroids. 20glz(  
Cataract prevalence rates in cross-sections I and II are HPM ggRs  
shown in Figure 1. The overall prevalence of cortical cataract 7P!<c/ E  
was 23.8% and 23.7% in cross-sections I and II,   -58  
respectively (age-sex adjusted P = 0.81). Corresponding xD[O8vQE  
prevalence of PSC was 6.3% and 6.0% for the two crosssections $-4OveS~B  
(age-sex adjusted P = 0.60). There was an Jo%5NXts4  
increased prevalence of nuclear cataract, from 18.7% in q1C) *8*g  
cross-section I to 23.9% in cross-section II over the 6-year @wa2Z  
period (age-sex adjusted P < 0.001). Prevalence of any cataract 1u4)  
(including persons who had cataract surgery), however, 0K/?8[#  
was relatively stable (46.9% and 46.8% in crosssections M=vRy|TL  
I and II, respectively). a%R'x]  
After age-standardization, these prevalence rates remained a:$hK%^ \  
stable for cortical cataract (23.8% and 23.5% in the two 6:Eu[PE~w  
surveys) and PSC (6.3% and 5.9%). The slightly increased e)Q{yO  
prevalence of nuclear cataract (from 18.7% to 24.2%) was {J_1.uN=  
not altered. Ur^~fW1 o  
Table 2 shows the age-specific prevalence rates for cortical y*i_Ec\h  
cataract, PSC and nuclear cataract in cross-sections I and ~M@'=Q*~  
II. A similar trend of increasing cataract prevalence with z@WuKRsi  
increasing age was evident for all three types of cataract in `U-i{i  
both surveys. Comparing the age-specific prevalence N!O.=>8<  
between the two surveys, a reduction in PSC prevalence in BK,h$z7#6  
cross-section II was observed in the older age groups (≥ 75 '3 B\ I#  
years). In contrast, increased nuclear cataract prevalence RPH]@  
in cross-section II was observed in the older age groups (≥ ,{4G@:Fm  
70 years). Age-specific cortical cataract prevalence was relatively }d<xbL!#  
consistent between the two surveys, except for a 6Xu^ cbD  
reduction in prevalence observed in the 80–84 age group DyZe+,g;S  
and an increasing prevalence in the older age groups (≥ 85 )HLe8:PG~  
years). m53XN  
Similar gender differences in cataract prevalence were &c;@u?:@S  
observed in both surveys (Table 3). Higher prevalence of >0#WkmRY  
cortical and nuclear cataract in women than men was evident Z_%9LxZlyj  
but the difference was only significant for cortical 'A#`,^]uLF  
cataract (age-adjusted odds ratio, OR, for women 1.3, S1_X@[t  
95% confidence intervals, CI, 1.1–1.5 in cross-section I =\jp%A1$  
and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con- 4Ji6B)B  
Table 1: Participant characteristics. BU\P5uB!V  
Characteristics Cross-section I Cross-section II {|Ew]Wq  
n % n % desrKnY  
Age (mean) (66.2) (66.7) f 7g?{M  
50–54 485 13.3 350 10.0 `5VEGSP]  
55–59 534 14.6 580 16.5 yJ(BPSt  
60–64 638 17.5 600 17.1 E=Z;T   
65–69 671 18.4 639 18.2 <r[5 S5y  
70–74 538 14.7 572 16.3 v0~'`*|&  
75–79 422 11.6 407 11.6 %RlG~a  
80–84 230 6.3 226 6.4 I-@A{vvPK  
85–89 100 2.7 110 3.1 HM'P<<  
90+ 36 1.0 24 0.7 :/F=j;o  
Female 2072 56.7 1998 57.0 ]_8 bX}_n  
Ever Smokers 1784 51.2 1789 51.2 2WKYf0t  
Use of inhaled steroids 370 10.94 478 13.8^ Idy {(Q  
History of: PEKU  
Diabetes 284 7.8 347 9.9^ zQ;jaS3 hf  
Hypertension 1669 46.0 1825 52.2^ AFd3_>h  
Emmetropia* 1558 42.9 1478 42.2 s-\.j-Sa  
Myopia* 442 12.2 495 14.1^ i|- 6  
Hyperopia* 1633 45.0 1532 43.7 7~gIOu  
n = number of persons affected Z0Tpz2m  
* best spherical equivalent refraction correction jRk" #:  
^ P < 0.01 X(sN+7DOV  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 >";I3S-t  
Page 4 of 7 \ O*8%  
(page number not for citation purposes) =5 a|'O  
t )oEHE7y  
rast, men had slightly higher PSC prevalence than women (qf%,F,_L  
in both cross-sections but the difference was not significant Gxtqzr*  
(OR 1.1, 95% CI 0.8–1.4 for men in cross-section I H$M#+EfL  
and OR 1.2, 95% 0.9–1.6 in cross-section II). /QA:`_</oh  
Discussion nnv&~C  
Findings from two surveys of BMES cross-sectional populations XXx]~m  
with similar age and gender distribution showed I$rn W  
that the prevalence of cortical cataract and PSC remained w=dTa5  
stable, while the prevalence of nuclear cataract appeared EWcqMD]4u  
to have increased. Comparison of age-specific prevalence, G*oqhep  
with totally independent samples within each age group, )D_\~n/5  
confirmed the robustness of our findings from the two =vd9mb-  
survey samples. Although lens photographs taken from K\bA[5+N  
the two surveys were graded for nuclear cataract by the 3lkz:]SsE  
same graders, who documented a high inter- and intragrader uBr^TM$k&  
reliability, we cannot exclude the possibility that xI'sprNa_1  
variations in photography, performed by different photographers, T-;|E^  
may have contributed to the observed difference ~d9R:t1  
in nuclear cataract prevalence. However, the overall uR;m<wPH,f  
Table 2: Age-specific prevalence of cataract types in cross sections I and II. C(4r>TNm  
Cataract type Age (years) Cross-section I Cross-section II <k 41j=d  
n % (95% CL)* n % (95% CL)* I%8>nMTJ  
Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2) [EdX6  
55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5) \& KfIh8  
60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8) '}F=U(!  
65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0) 3Z taj^v  
70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6) ['`Vg=O.{  
75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1) >j%4U*  
80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6) MBjo9P(  
85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5) Xb/W[rcs  
90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2) B %L dH  
PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0) *(w#*,lv  
55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9) t,v=~LE  
60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6) UA%tI2  
65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3) 3|Vh[iAa\  
70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3) P { 8d.  
75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7) IXz)xdP  
80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2) 5nQxVwY  
85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4) u3VSS4RG%  
90+ 23 21.7 (3.5–40.0) 11 0.0 Z~s" =kF,  
Nuclear 50–54 323 1.6 (0.2–2.9) 331 0.9 (–0.2–1.9) r ?e''r  
55–59 386 2.3 (0.8–3.8) 507 3.6 (1.9–5.2) 9_/dj"5  
60–64 453 5.3 (3.2–7.4) 501 11.6 (8.8–14.4) k~|5TO  
65–69 478 17.2 (13.8–20.1) 534 18.5 (15.2–21.9) Ln3<r&&Jz  
70–74 392 27.6 (23.1–32.0) 453 36.0 (31.6–40.4) 5(qc_~p^  
75–79 255 45.1 (39.0–51.3) 302 55.6 (50.0–61.3) .!><qV g  
80–84 146 54.1 (45.9–62.3) 147 73.5 (66.3–80.7) k% -S7iQ  
85–89 50 64.0 (50.2–77.8) 70 80.0 (70.4–89.6) &>KZ4%&?  
90+ 18 72.2 (49.3–95.1) 15 73.3 (48.0–98.7) k O8W>  
n = number of persons %s(Ri6R&  
* 95% Confidence Limits ;bh[TmQTJ  
Cataract FMioguunrtea i1n ps rEeyvea lSetnucdey in cross-sections I and II of the Blue vf&Sk`  
Cataract prevalence in cross-sections I and II of the Blue Zf [#~4  
Mountains Eye Study. ndB [f  
0 >ow5aOlQ&  
10 4!,`|W1  
20 U5f<4I  
30 S(Ej:  H  
40 6Y 4I $[  
50 o$[alh;c+W  
cortical PSC nuclear any 0.4Q-?J  
cataract JPt0k  
Cataract type {r.yoI4e  
% 3R|C$+Sc  
Cross-section I )8244;  
Cross-section II fg8"fbG`:  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 dh.vZ0v=7  
Page 5 of 7 X7~AqG  
(page number not for citation purposes) I"Gr<?r  
prevalence of any cataract (including cataract surgery) was bFt$u]Yvo  
relatively stable over the 6-year period. Kz`g Q|S  
Although different population-based studies used different {;0+N -U  
grading systems to assess cataract [15], the overall J<'7z%2w  
prevalence of the three cataract types were similar across r:QLO~l/  
different study populations [12,16-23]. Most studies have n\x@~ SzrX  
suggested that nuclear cataract is the most prevalent type \as^z!<  
of cataract, followed by cortical cataract [16-20]. Ours and j1 Q"s(  
other studies reported that cortical cataract was the most $^XCI%DH  
prevalent type [12,21-23]. VBe.&b8  
Our age-specific prevalence data show a reduction of S7 fX1y[  
15.9% in cortical cataract prevalence for the 80–84 year @UG%B7  
age group, concordant with an increase in cataract surgery Tz"Xm/Gy  
prevalence by 9% in those aged 80+ years observed in the .dvOUt I[  
same study population [10]. Although cortical cataract is S~+er{,ht4  
thought to be the least likely cataract type leading to a cataract FO/ [7ZH  
surgery, this may not be the case in all older persons. ]g0h7q)79  
A relatively stable cortical cataract and PSC prevalence }+wvZq +c  
over the 6-year period is expected. We cannot offer a r`8>@2sW1  
definitive explanation for the increase in nuclear cataract =bwuLno>  
prevalence. A possible explanation could be that a moderate <8[y2|UBt  
level of nuclear cataract causes less visual disturbance :w+2L4lGs  
than the other two types of cataract, thus for the oldest age HLYTt)f}  
groups, persons with nuclear cataract could have been less !eH9LRp  
likely to have surgery unless it is very dense or co-existing GqT 0SP  
with cortical cataract or PSC. Previous studies have shown Mk Cq$M A  
that functional vision and reading performance were high mTsl"A>  
in patients undergoing cataract surgery who had nuclear X4bB  
cataract only compared to those with mixed type of cataract # {'1\@q  
(nuclear and cortical) or PSC [24,25]. In addition, the U fzA/  
overall prevalence of any cataract (including cataract surgery) hj_%'kk-A  
was similar in the two cross-sections, which appears l^$8;$Rq  
to support our speculation that in the oldest age group, Y 4 <  
nuclear cataract may have been less likely to be operated @2>j4Sc  
than the other two types of cataract. This could have F.%g_Xvk:  
resulted in an increased nuclear cataract prevalence (due .-[d6Pnw  
to less being operated), compensated by the decreased mK>c+ u)  
prevalence of cortical cataract and PSC (due to these being V:wx@9m)  
more likely to be operated), leading to stable overall prevalence 1$]hyC/f  
of any cataract. Xaca=tsO  
Possible selection bias arising from selective survival @/w ($w"  
among persons without cataract could have led to underestimation j%V95M% $  
of cataract prevalence in both surveys. We oOU?6nq  
assume that such an underestimation occurred equally in !}TZmwf'  
both surveys, and thus should not have influenced our j?YZOO>X  
assessment of temporal changes. E `D sRR <  
Measurement error could also have partially contributed QQB\$[M!Z  
to the observed difference in nuclear cataract prevalence. F_?aoP&5  
Assessment of nuclear cataract from photographs is a "|\G[xLOaW  
potentially subjective process that can be influenced by S"/M+m+ ]  
variations in photography (light exposure, focus and the h5x_Vjj  
slit-lamp angle when the photograph was taken) and _"Bh 3 7  
grading. Although we used the same Topcon slit-lamp I`~ofq?r  
camera and the same two graders who graded photos Do3g^RD#  
from both surveys, we are still not able to exclude the possibility K)z! e;r  
of a partial influence from photographic variation YCWt%a*I'  
on this result. R43yr+p  
A similar gender difference (women having a higher rate C_&-2Z  
than men) in cortical cataract prevalence was observed in " wB~* ,Ny  
both surveys. Our findings are in keeping with observations *G<K@k  
from the Beaver Dam Eye Study [18], the Barbados AWY#t&  
Eye Study [22] and the Lens Opacities Case-Control nO'lN<L  
Group [26]. It has been suggested that the difference &<s[(w!%%  
could be related to hormonal factors [18,22]. A previous xUiSAKrcM  
study on biochemical factors and cataract showed that a Vm_waa  
lower level of iron was associated with an increased risk of ,:Q+>h  
cortical cataract [27]. No interaction between sex and biochemical nkv+O$LXP  
factors were detected and no gender difference L=ala1{O  
was assessed in this study [27]. The gender difference seen $rb #k{  
in cortical cataract could be related to relatively low iron l;N?*2zm[  
levels and low hemoglobin concentration usually seen in * [\H)Lz  
women [28]. Diabetes is a known risk factor for cortical Y [hTO.LF  
Table 3: Gender distribution of cataract types in cross-sections I and II. O0"u-UX{  
Cataract type Gender Cross-section I Cross-section II yJ\K\\]  
n % (95% CL)* n % (95% CL)* 3C+!Y#F  
Cortical Male 1496 21.1 (19.0–23.1) 1328 20.4 (18.2–22.6) G,VTFM6  
Female 1939 25.9 (23.9–27.8) 1785 26.2 (24.2–28.3) IQ${2Dpg[  
PSC Male 1500 6.5 (5.2–7.7) 1314 6.4 (5.1–7.7) mHm"QBa!  
Female 1944 6.2 (5.1–7.2) 1753 5.7 (4.6–6.7) pyW&`(]S  
Nuclear Male 1106 17.6 (15.4–19.9) 1225 22.5 (20.1–24.8) XM9}ax  
Female 1395 19.5 (17.4–21.6) 1635 25.0 (22.9–27.1) |>/T*zk<  
n = number of persons Rl. YF+YH  
* 95% Confidence Limits =B0#z]qu  
BMC Ophthalmology 2006, 6:17 http://www.biomedcentral.com/1471-2415/6/17 Z{9 mZ lIy  
Page 6 of 7 Ewfzjc   
(page number not for citation purposes) +"u6+[E  
cataract but in this particular population diabetes is more F8c^M</  
prevalent in men than women in all age groups [29]. Differential F%Xj'=  
exposures to cataract risk factors or different dietary SuO@LroxTB  
or lifestyle patterns between men and women may &<oZl.T  
also be related to these observations and warrant further $CgJ+ua\8  
study. ^an3&  
Conclusion 4Jf6uhaE  
In summary, in two population-based surveys 6 years q ,C)AZ  
apart, we have documented a relatively stable prevalence Vy- kogVt  
of cortical cataract and PSC over the period. The observed 5._=m"Pl  
overall increased nuclear cataract prevalence by 5% over a .4t-5,7s%  
6-year period needs confirmation by future studies, and M%\=Fb  
reasons for such an increase deserve further study. <b5J"i&m  
Competing interests -0 e&>H%  
The author(s) declare that they have no competing interests. hC nqe  
Authors' contributions e >OYJd0s  
AGT graded the photographs, performed literature search j06Xz\c  
and wrote the first draft of the manuscript. JJW graded the J:N4F.o&K  
photographs, critically reviewed and modified the manuscript. qoifzEc`U  
ER performed the statistical analysis and critically *c 0\<BI  
reviewed the manuscript. PM designed and directed the tn"n~;Bh?:  
study, adjudicated cataract cases and critically reviewed 6v]y\+  
and modified the manuscript. All authors read and y [pU8QSt  
approved the final manuscript. OYj4G ?c  
Acknowledgements hj8S".A_  
This study was supported by the Australian National Health & Medical >z,SN  
Research Council, Canberra, Australia (Grant Nos 974159, 991407). The pejG%pJ  
abstract was presented at the Association for Research in Vision and Ophthalmology miq"3  
(ARVO) meeting in Fort Lauderdale, Florida, USA, May 2005. 1]yjhw9g  
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