BioMed Central
.c',?[S/vH Page 1 of 7
<k)rfv7 (page number not for citation purposes)
=l\D7s BMC Ophthalmology
4f1*?HX& Research article Open Access
2vur_`cV Comparison of age-specific cataract prevalence in two
1]qhQd-u population-based surveys 6 years apart
"44X'G8N Ava Grace Tan†, Jie Jin Wang*†, Elena Rochtchina† and Paul Mitchell†
`,|7X]%b Address: Centre for Vision Research, Westmead Millennium Institute, Department of Ophthalmology, University of Sydney, Westmead Hospital,
e5AiIVlv Westmead, NSW, Australia
eC3ZK"oJ Email: Ava Grace Tan -
ava_tan@wmi.usyd.edu.au; Jie Jin Wang* -
jiejin_wang@wmi.usyd.edu.au;
's9)\LS>p Elena Rochtchina -
elena_rochtchina@wmi.usyd.edu.au; Paul Mitchell -
paul_mitchell@wmi.usyd.edu.au m3,v&Z * Corresponding author †Equal contributors
w,P2_xk` Abstract
"B\qp "N Background: In this study, we aimed to compare age-specific cortical, nuclear and posterior
`yf#(YP subcapsular (PSC) cataract prevalence in two surveys 6 years apart.
`fL$t0" Methods: The Blue Mountains Eye Study examined 3654 participants (82.4% of those eligible) in
"{&!fD~w cross-section I (1992–4) and 3509 participants (75.1% of survivors and 85.2% of newly eligible) in
VMNihx0FJ cross-section II (1997–2000, 66.5% overlap with cross-section I). Cataract was assessed from lens
U"ZDt photographs following the Wisconsin Cataract Grading System. Cortical cataract was defined if
S4\T ( cortical opacity comprised ≥ 5% of lens area. Nuclear cataract was defined if nuclear opacity ≥
oZIoY*7IrQ Wisconsin standard 4. PSC was defined if any present. Any cataract was defined to include persons
j#Y8h5r who had previous cataract surgery. Weighted kappa for inter-grader reliability was 0.82, 0.55 and
-Z#A
}h 0.82 for cortical, nuclear and PSC cataract, respectively. We assessed age-specific prevalence using
\_+d*hHF~ an interval of 5 years, so that participants within each age group were independent between the
KI#hII[Q. two surveys.
FkRrW^?5G Results: Age and gender distributions were similar between the two populations. The age-specific
DQE.;0ld prevalence of cortical (23.8% in 1st, 23.7% in 2nd) and PSC cataract (6.3%, 6.0%) was similar. The
h-6kf:XP% prevalence of nuclear cataract increased slightly from 18.7% to 23.9%. After age standardization,
PsTwJLY the similar prevalence of cortical (23.8%, 23.5%) and PSC cataract (6.3%, 5.9%), and the increased
:lcoS J prevalence of nuclear cataract (18.7%, 24.2%) remained.
"d{ |_Cf Conclusion: In two surveys of two population-based samples with similar age and gender
jirxzj distributions, we found a relatively stable cortical and PSC cataract prevalence over a 6-year period.
m. XLpD The increased prevalence of nuclear cataract deserves further study.
RCsd Background
n}YRE`>D Age-related cataract is the leading cause of reversible visual
}PoB`H'K5 impairment in older persons [1-6]. In Australia, it is
4Sw)IU~K( estimated that by the year 2021, the number of people
sqsBGFeG affected by cataract will increase by 63%, due to population
lh
.p`^v aging [7]. Surgical intervention is an effective treatment
k|&@xEbS
for cataract and normal vision (> 20/40) can usually
V+DN<F- be restored with intraocular lens (IOL) implantation.
P0|V1,) Cataract surgery with IOL implantation is currently the
}+,;wj~ most commonly performed, and is, arguably, the most
RtN5\ cost effective surgical procedure worldwide. Performance
kWF, *@.B Published: 20 April 2006
s_u@8e 6_ BMC Ophthalmology 2006, 6:17 doi:10.1186/1471-2415-6-17
Hh,q)(Wo Received: 14 December 2005
g&X$)V4C Accepted: 20 April 2006
yX/ 9jk This article is available from:
http://www.biomedcentral.com/1471-2415/6/17 a!]'S4JS © 2006 Tan et al; licensee BioMed Central Ltd.
RYy_Ppn96f This is an Open Access article distributed under the terms of the Creative Commons Attribution License (
http://creativecommons.org/licenses/by/2.0),
/0@'8f\I which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
3+0$=ef BMC Ophthalmology 2006, 6:17
http://www.biomedcentral.com/1471-2415/6/17 3D(/k%;) Page 2 of 7
3Oy?_a$ (page number not for citation purposes)
COZ<^*=A#p of this surgical procedure has been continuously increasing
5PqL#Eu`! in the last two decades. Data from the Australian
2ntL7F<ow Health Insurance Commission has shown a steady
V+(1U|@~
increase in Medicare claims for cataract surgery [8]. A 2.6-
z;J"3kM fold increase in the total number of cataract procedures
JUHmIFjZ from 1985 to 1994 has been documented in Australia [9].
Q9Sh2qF^2 The rate of cataract surgery per thousand persons aged 65
W9+H/T7! years or older has doubled in the last 20 years [8,9]. In the
OWx-I\: Blue Mountains Eye Study population, we observed a onethird
B<%cqz@ increase in cataract surgery prevalence over a mean
5bKM}?=L 6-year interval, from 6% to nearly 8% in two cross-sectional
NO+.n)etGb population-based samples with a similar age range
H,u {zU') [10]. Further increases in cataract surgery performance
&{-r 5d23 would be expected as a result of improved surgical skills
}OL?k/w and technique, together with extending cataract surgical
B]iPixA6 benefits to a greater number of older people and an
q!iSY increased number of persons with surgery performed on
~.7/o0'+ both eyes.
4z%::? Both the prevalence and incidence of age-related cataract
jlXzfDT link directly to the demand for, and the outcome of, cataract
>xsbXQ>. surgery and eye health care provision. This report
<hkSbJF aimed to assess temporal changes in the prevalence of cortical
F#-mseKhc and nuclear cataract and posterior subcapsular cataract
[J{\Ke0<e1 (PSC) in two cross-sectional population-based
QP>tu1B| surveys 6 years apart.
\no6
]xN; Methods
J'}G~rB<< The Blue Mountains Eye Study (BMES) is a populationbased
*uW l 804 cohort study of common eye diseases and other
w.X MyHj health outcomes. The study involved eligible permanent
Aqy y\G; residents aged 49 years and older, living in two postcode
![3 /! areas in the Blue Mountains, west of Sydney, Australia.
%B}<5iO Participants were identified through a census and were
L!;"73,&(8 invited to participate. The study was approved at each
QQI,$HId stage of the data collection by the Human Ethics Committees
B_Ul&V of the University of Sydney and the Western Sydney
z][hlDv\j Area Health Service and adhered to the recommendations
S@Iza9\|@ of the Declaration of Helsinki. Written informed consent
QHU|aC{r was obtained from each participant.
/ <C{$Gu Details of the methods used in this study have been
)d~{gPr. described previously [11]. The baseline examinations
(n{x"rLy/ (BMES cross-section I) were conducted during 1992–
d4~;!#< 1994 and included 3654 (82.4%) of 4433 eligible residents.
b1TIVK3m Follow-up examinations (BMES IIA) were conducted
dl]pdg< during 1997–1999, with 2335 (75.0% of BMES
D~ogq] cross section I survivors) participating. A repeat census of
O*7vmPy the same area was performed in 1999 and identified 1378
pKtN$Fd newly eligible residents who moved into the area or the
CZ33|w eligible age group. During 1999–2000, 1174 (85.2%) of
I1pnF61U this group participated in an extension study (BMES IIB).
9r.h^ BMES cross-section II thus includes BMES IIA (66.5%)
`5Bv2wlIV and BMES IIB (33.5%) participants (n = 3509).
N_^PoX935O Similar procedures were used for all stages of data collection
m#Ydq(0+ at both surveys. A questionnaire was administered
O llS including demographic, family and medical history. A
Z=9<esx detailed eye examination included subjective refraction,
38 ]}+Bb slit-lamp (Topcon SL-7e camera, Topcon Optical Co,
4Ei8G]O
$_ Tokyo, Japan) and retroillumination (Neitz CT-R camera,
1Q_Q-Z Neitz Instrument Co, Tokyo, Japan) photography of the
0u;a*#V @ lens. Grading of lens photographs in the BMES has been
Bs`mzA54 previously described [12]. Briefly, masked grading was
C$0rl74Wi performed on the lens photographs using the Wisconsin
sYhHh$mwA Cataract Grading System [13]. Cortical cataract and PSC
,\?s=D{ were assessed from the retroillumination photographs by
v2IcDz`}7 estimating the percentage of the circular grid involved.
7Ll?#eun Cortical cataract was defined when cortical opacity
j0=F__H#@ involved at least 5% of the total lens area. PSC was defined
Lv?jg?$ when opacity comprised at least 1% of the total lens area.
We++DWp Slit-lamp photographs were used to assess nuclear cataract
O>N/6Z using the Wisconsin standard set of four lens photographs
Im?/#t X [13]. Nuclear cataract was defined when nuclear opacity
`$Um was at least as great as the standard 4 photograph. Any cataract
&xt[w>/i was defined to include persons who had previous
d
eQ { cataract surgery as well as those with any of three cataract
{Q>4zepN! types. Inter-grader reliability was high, with weighted
cTz@ga;!mI kappa 0.82 for cortical cataract, 0.55 (simple kappa 0.75)
&.(iS for nuclear cataract and 0.82 for PSC grading. The intragrader
|"PS e~ u reliability for nuclear cataract was assessed with
dU*$V7 simple kappa 0.83 for the senior grader who graded
tU$n3Bg nuclear cataract at both surveys. All PSC cases were confirmed
H,W8JNPs by an ophthalmologist (PM).
pP#D*hiP-g In cross-section I, 219 persons (6.0%) had missing or
}.(DQwC}1k ungradable Neitz photographs, leaving 3435 with photographs
yZ!~m3Q available for cortical cataract and PSC assessment,
C?k\5AzT while 1153 (31.6%) had randomly missing or ungradable
s$zm)y5 Topcon photographs due to a camera malfunction, leaving
TQ:h[6v 2501 with photographs available for nuclear cataract
{\`y)k 7 assessment. Comparison of characteristics between participants
kOdA8XRY with and without Neitz or Topcon photographs in
TV0sxod6 cross-section I showed no statistically significant differences
1;KJUf[N between the two groups, as reported previously
*P5\T4!+d [12]. In cross-section II, 441 persons (12.5%) had missing
N iu
|M@ or ungradable Neitz photographs, leaving 3068 for cortical
).`v&-cK4E cataract and PSC assessment, and 648 (18.5%) had
1JUj e missing or ungradable Topcon photographs, leaving 2860
|QF_E4ISD for nuclear cataract assessment.
* ] Data analysis was performed using the Statistical Analysis
wd32q7lGo1 System (SAS, SAS Institute, Cary, NC, USA). Age-adjusted
[3sZ=)G prevalence was calculated using direct standardization of
e v0>j4Q the cross-section II population to the cross-section I population.
F+*fim'NK We assessed age-specific prevalence using an
9D &vxKE interval of 5 years, so that participants within each age
*/JYP + group were independent between the two cross-sectional
rW|%eT*/'A surveys.
d>mT+{3 BMC Ophthalmology 2006, 6:17
http://www.biomedcentral.com/1471-2415/6/17 j!NXNuy: Page 3 of 7
aeI0;u (page number not for citation purposes)
*!TQC6b$ Results
jjQDw=6 Characteristics of the two survey populations have been
TBrwir previously compared [14] and showed that age and sex
!q,7@W3i distributions were similar. Table 1 compares participant
_&\
'Va$ characteristics between the two cross-sections. Cross-section
f8SO:ihXL II participants generally had higher rates of diabetes,
i].E1},% hypertension, myopia and more users of inhaled steroids.
K?[Vz[-Fc Cataract prevalence rates in cross-sections I and II are
Tn/Z s| shown in Figure 1. The overall prevalence of cortical cataract
?>{u@tYL was 23.8% and 23.7% in cross-sections I and II,
E:M,nSc)53 respectively (age-sex adjusted P = 0.81). Corresponding
6it
[i@*" prevalence of PSC was 6.3% and 6.0% for the two crosssections
)eT>[['fm (age-sex adjusted P = 0.60). There was an
#]5KWXC'~ increased prevalence of nuclear cataract, from 18.7% in
||*F.p cross-section I to 23.9% in cross-section II over the 6-year
1kpw*$P0 period (age-sex adjusted P < 0.001). Prevalence of any cataract
K> 4w (including persons who had cataract surgery), however,
)`{m |\b was relatively stable (46.9% and 46.8% in crosssections
QEbf]U= I and II, respectively).
nyqX\m- After age-standardization, these prevalence rates remained
7gV9m9 # stable for cortical cataract (23.8% and 23.5% in the two
"_LqIW1 surveys) and PSC (6.3% and 5.9%). The slightly increased
=No#/_ prevalence of nuclear cataract (from 18.7% to 24.2%) was
)92(C not altered.
D@9 +yu=S Table 2 shows the age-specific prevalence rates for cortical
DiOd!8Y cataract, PSC and nuclear cataract in cross-sections I and
1eV&oN# II. A similar trend of increasing cataract prevalence with
xRgdU+,Mj increasing age was evident for all three types of cataract in
lb}RPvQE both surveys. Comparing the age-specific prevalence
0wNlt#G;{ between the two surveys, a reduction in PSC prevalence in
Kw;gQk~R! cross-section II was observed in the older age groups (≥ 75
_V1:'T8 years). In contrast, increased nuclear cataract prevalence
w{dRf!b69 in cross-section II was observed in the older age groups (≥
_*?qOmf= 70 years). Age-specific cortical cataract prevalence was relatively
f 42F@M(: consistent between the two surveys, except for a
UP)<(3YA reduction in prevalence observed in the 80–84 age group
'Ca;gi !U and an increasing prevalence in the older age groups (≥ 85
'"\n,
3h years).
L5zCL0j` Similar gender differences in cataract prevalence were
"5k6FV observed in both surveys (Table 3). Higher prevalence of
$
-<(geI cortical and nuclear cataract in women than men was evident
)4qspy3 but the difference was only significant for cortical
c CDT27@ cataract (age-adjusted odds ratio, OR, for women 1.3,
Ck
!"MK4 95% confidence intervals, CI, 1.1–1.5 in cross-section I
{D",ao
and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con-
X)iI] Table 1: Participant characteristics.
L>1y[
Q Characteristics Cross-section I Cross-section II
/1{:uh$ n % n %
?.F^Oi6
u Age (mean) (66.2) (66.7)
A'~mJO/ 50–54 485 13.3 350 10.0
!lFNG:&` 55–59 534 14.6 580 16.5
65O 8?I 60–64 638 17.5 600 17.1
O%>*=h`P 65–69 671 18.4 639 18.2
i ?M-~EKu 70–74 538 14.7 572 16.3
R\7r!38 75–79 422 11.6 407 11.6
EZ"i0u 80–84 230 6.3 226 6.4
j5:4/vD 85–89 100 2.7 110 3.1
x`C"Z7t 90+ 36 1.0 24 0.7
.xT{Rz Female 2072 56.7 1998 57.0
}AB_i'C0 Ever Smokers 1784 51.2 1789 51.2
MbInXv$q2/ Use of inhaled steroids 370 10.94 478 13.8^
Vq-Kl[-| History of:
YRBJ(v"9 Diabetes 284 7.8 347 9.9^
~4Fz A,, Hypertension 1669 46.0 1825 52.2^
;P ju O Emmetropia* 1558 42.9 1478 42.2
WFk%nO/ Myopia* 442 12.2 495 14.1^
)i:*r8*~ Hyperopia* 1633 45.0 1532 43.7
QP50.P5g n = number of persons affected
6qTMHRI * best spherical equivalent refraction correction
B?^~1Ua9Zv ^ P < 0.01
j-**\.4a~ BMC Ophthalmology 2006, 6:17
http://www.biomedcentral.com/1471-2415/6/17 -u"|{5? ' Page 4 of 7
03zt^< (page number not for citation purposes)
4<PupJ t
*$DD+]2 rast, men had slightly higher PSC prevalence than women
' ,]Aj!q in both cross-sections but the difference was not significant
Qt>kythi (OR 1.1, 95% CI 0.8–1.4 for men in cross-section I
d(RMD and OR 1.2, 95% 0.9–1.6 in cross-section II).
c*zeO@AAn Discussion
i!UT = Findings from two surveys of BMES cross-sectional populations
-
(((y)! with similar age and gender distribution showed
TTa3DbFp% that the prevalence of cortical cataract and PSC remained
VrfEa d stable, while the prevalence of nuclear cataract appeared
&XI9%h9| to have increased. Comparison of age-specific prevalence,
_](y<O^9yO with totally independent samples within each age group,
9-_Lc< confirmed the robustness of our findings from the two
VCnf`wZB" survey samples. Although lens photographs taken from
: 4-pnn the two surveys were graded for nuclear cataract by the
:~W(#T,$E same graders, who documented a high inter- and intragrader
V"K.s2U^ reliability, we cannot exclude the possibility that
3w p@OF_ variations in photography, performed by different photographers,
Z{l`X#': may have contributed to the observed difference
4:O.x#p in nuclear cataract prevalence. However, the overall
ft@#[Bkx Table 2: Age-specific prevalence of cataract types in cross sections I and II.
A
Rnq~E@1 Cataract type Age (years) Cross-section I Cross-section II
t(PA+~sIp n % (95% CL)* n % (95% CL)*
A-L)2.M Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2)
hMS:t(N{ 55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5)
wi.E$RckD 60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8)
n.NWS/v_{ 65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0)
jg%mWiKwK7 70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6)
G[>CBh5 75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1)
kt_O= 80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6)
%cDTq&Q 85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5)
9)=bBQyr: 90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2)
C-,#t5eir PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0)
}c=Y<Cdh
55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9)
/?Y4C)G 60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6)
y!S:d 65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3)
4/3w
* 70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3)
$JBb]
v8_ 75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7)
@J^
Oy
3z 80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2)
9|@5eN:N 85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4)
#ifjQ7(: 90+ 23 21.7 (3.5–40.0) 11 0.0
>XuPg(Ow Nuclear 50–54 323 1.6 (0.2–2.9) 331 0.9 (–0.2–1.9)
? uP5("c 55–59 386 2.3 (0.8–3.8) 507 3.6 (1.9–5.2)
&"Cy&[ 60–64 453 5.3 (3.2–7.4) 501 11.6 (8.8–14.4)
apM)$ 65–69 478 17.2 (13.8–20.1) 534 18.5 (15.2–21.9)
+m~3InW
q 70–74 392 27.6 (23.1–32.0) 453 36.0 (31.6–40.4)
SjA'<ZX>TM 75–79 255 45.1 (39.0–51.3) 302 55.6 (50.0–61.3)
+yk 0ez 80–84 146 54.1 (45.9–62.3) 147 73.5 (66.3–80.7)
)N3/;U; 85–89 50 64.0 (50.2–77.8) 70 80.0 (70.4–89.6)
LKZ<\%
X 90+ 18 72.2 (49.3–95.1) 15 73.3 (48.0–98.7)
|vG?H#y n = number of persons
e!C,<W&B\ * 95% Confidence Limits
!T~uxeZ/; Cataract FMioguunrtea i1n ps rEeyvea lSetnucdey in cross-sections I and II of the Blue
ao(Lv+
Cataract prevalence in cross-sections I and II of the Blue
,]9p&xu Mountains Eye Study.
7g o Rj 0
SD:Bw0gzrI 10
2Mw` 20
z<yqQ
[ 30
2`FDY3n 40
j&8GtE1b 50
-B7X;{
cortical PSC nuclear any
&t6SI' cataract
{irl}EeyC Cataract type
:F"NF %
@lh]?|*[ Cross-section I
(ze9-!% Cross-section II
Ogh, BMC Ophthalmology 2006, 6:17
http://www.biomedcentral.com/1471-2415/6/17 Ycxv=Et Page 5 of 7
@zt "Y~9i (page number not for citation purposes)
Gch3|e prevalence of any cataract (including cataract surgery) was
n2'XWbMaL relatively stable over the 6-year period.
h
b)83mH} Although different population-based studies used different
kidv^`.H$w grading systems to assess cataract [15], the overall
4/2@^\?i) prevalence of the three cataract types were similar across
jnFN{(VH different study populations [12,16-23]. Most studies have
z<cPy)F]" suggested that nuclear cataract is the most prevalent type
vsB3n$2@u of cataract, followed by cortical cataract [16-20]. Ours and
bWZzb& other studies reported that cortical cataract was the most
OZ<fQf.Gh} prevalent type [12,21-23].
!]z4'* )W Our age-specific prevalence data show a reduction of
]4\6_J& 15.9% in cortical cataract prevalence for the 80–84 year
7U&<{U< age group, concordant with an increase in cataract surgery
ZYTBc#f prevalence by 9% in those aged 80+ years observed in the
'H1k same study population [10]. Although cortical cataract is
H"pwIiC thought to be the least likely cataract type leading to a cataract
lO1]P&@ surgery, this may not be the case in all older persons.
RAxp2uif A relatively stable cortical cataract and PSC prevalence
d}^hZ8k| over the 6-year period is expected. We cannot offer a
j>hBNz definitive explanation for the increase in nuclear cataract
Fe
ZGPxc~ prevalence. A possible explanation could be that a moderate
z{U^j:A level of nuclear cataract causes less visual disturbance
(/_w23rr than the other two types of cataract, thus for the oldest age
,e*WJh8k[ groups, persons with nuclear cataract could have been less
<EuS6Pg likely to have surgery unless it is very dense or co-existing
MeO2 cy!5q with cortical cataract or PSC. Previous studies have shown
0P4g6t}e that functional vision and reading performance were high
Y0o{@)Y: in patients undergoing cataract surgery who had nuclear
7<93n`byM cataract only compared to those with mixed type of cataract
VzuU0 (nuclear and cortical) or PSC [24,25]. In addition, the
42PA?^xPw overall prevalence of any cataract (including cataract surgery)
%? O$xQ.< was similar in the two cross-sections, which appears
&f/"ir[8i to support our speculation that in the oldest age group,
G,@Jo[e nuclear cataract may have been less likely to be operated
H66F4i than the other two types of cataract. This could have
f"G-',O< resulted in an increased nuclear cataract prevalence (due
hsZ@)[/: to less being operated), compensated by the decreased
E
q
t\It9 prevalence of cortical cataract and PSC (due to these being
{$_Gjv more likely to be operated), leading to stable overall prevalence
zIc_'Z,b of any cataract.
A 1aN<!ehB Possible selection bias arising from selective survival
FND+Ok& among persons without cataract could have led to underestimation
I=4G+h5p of cataract prevalence in both surveys. We
zw%1a 3! assume that such an underestimation occurred equally in
U%aDkC+M both surveys, and thus should not have influenced our
i [2bz+Z? assessment of temporal changes.
eY'RDQa Measurement error could also have partially contributed
2;ac&j1 to the observed difference in nuclear cataract prevalence.
_>Oc>.MB Assessment of nuclear cataract from photographs is a
?l](RI
potentially subjective process that can be influenced by
tx}=c5 variations in photography (light exposure, focus and the
(iu IeJ^Z slit-lamp angle when the photograph was taken) and
+qM2&M grading. Although we used the same Topcon slit-lamp
gq&jNj7V camera and the same two graders who graded photos
vH>s2\V" from both surveys, we are still not able to exclude the possibility
'F Cmbry of a partial influence from photographic variation
=nG>aAG on this result.
zB#.EW A similar gender difference (women having a higher rate
sO8F0@%aH( than men) in cortical cataract prevalence was observed in
G,,f' > both surveys. Our findings are in keeping with observations
XOPiwrg%p from the Beaver Dam Eye Study [18], the Barbados
n<DZb`/uHZ Eye Study [22] and the Lens Opacities Case-Control
GBGna3 Group [26]. It has been suggested that the difference
HXQ
}B$V could be related to hormonal factors [18,22]. A previous
Lv:;} study on biochemical factors and cataract showed that a
{R5_=MG lower level of iron was associated with an increased risk of
dp*E#XCr1 cortical cataract [27]. No interaction between sex and biochemical
T&]IPOH9 factors were detected and no gender difference
F&D,y-CQ was assessed in this study [27]. The gender difference seen
jluv}*If in cortical cataract could be related to relatively low iron
Twpk@2=l levels and low hemoglobin concentration usually seen in
eY3<LVAX women [28]. Diabetes is a known risk factor for cortical
K,@} 'N Table 3: Gender distribution of cataract types in cross-sections I and II.
dG}*M25 Cataract type Gender Cross-section I Cross-section II
8,]wOxwqi n % (95% CL)* n % (95% CL)*
82yfPQ&UI Cortical Male 1496 21.1 (19.0–23.1) 1328 20.4 (18.2–22.6)
I\('b9"* Female 1939 25.9 (23.9–27.8) 1785 26.2 (24.2–28.3)
"VA'W/yv! PSC Male 1500 6.5 (5.2–7.7) 1314 6.4 (5.1–7.7)
lYy:A%yDT Female 1944 6.2 (5.1–7.2) 1753 5.7 (4.6–6.7)
C0H@ Nuclear Male 1106 17.6 (15.4–19.9) 1225 22.5 (20.1–24.8)
qex::Qf Female 1395 19.5 (17.4–21.6) 1635 25.0 (22.9–27.1)
UW-`
k1 n = number of persons
6\6g-1B` * 95% Confidence Limits
#QiNSS BMC Ophthalmology 2006, 6:17
http://www.biomedcentral.com/1471-2415/6/17 m0JJPBp Page 6 of 7
)?k~E=&o