BioMed Central
,?<h] !aQ Page 1 of 7
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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-\e U 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
a EFe!_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
3vRLg 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:3ZPZC 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
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_-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
^dFhg_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
jH(&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)O Uy 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
NIaF 5z 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$M(^)l during 1997–1999, with 2335 (75.0% of BMES
h8jB=e, H cross section I survivors) participating. A repeat census of
W^k,Pmopy the same area was performed in 1999 and identified 1378
;%WdvnW newly eligible residents who moved into the area or the
(i]Z|@|) eligible age group. During 1999–2000, 1174 (85.2%) of
v,jhE9_O0 this group participated in an extension study (BMES IIB).
Oc~aW3*A( BMES cross-section II thus includes BMES IIA (66.5%)
3fp> 4;ym' and BMES IIB (33.5%) participants (n = 3509).
\2>?6zs Similar procedures were used for all stages of data collection
I+",b4 at both surveys. A questionnaire was administered
OJpj}R including demographic, family and medical history. A
;&
|qSa' detailed eye examination included subjective refraction,
gu<V(M\ slit-lamp (Topcon SL-7e camera, Topcon Optical Co,
[7.agI@= Tokyo, Japan) and retroillumination (Neitz CT-R camera,
H\#:,s {1 Neitz Instrument Co, Tokyo, Japan) photography of the
){ gAj lens. Grading of lens photographs in the BMES has been
XYAm
J previously described [12]. Briefly, masked grading was
m$:&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)
.CbGDZ 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
<@uOCRbV 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
U4,2 br
> [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.
<,1fkq>, 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
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~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,
xK%= 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$
eB ,~
Table 2 shows the age-specific prevalence rates for cortical
4jmK]. 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$X7m
70 years). Age-specific cortical cataract prevalence was relatively
<|6%9@ consistent between the two surveys, except for a
NY reduction in prevalence observed in the 80–84 age group
5rxA<Gs and an increasing prevalence in the older age groups (≥ 85
N"5fmY< years).
P1kB>"bR Similar gender differences in cataract prevalence were
IfdI|ya observed in both surveys (Table 3). Higher prevalence of
dXvt6kF cortical and nuclear cataract in women than men was evident
Q'NmSX)0 but the difference was only significant for cortical
.=RlOK cataract (age-adjusted odds ratio, OR, for women 1.3,
t={0( 95% confidence intervals, CI, 1.1–1.5 in cross-section I
{[G`Z9]z&- and OR 1.4, 95% CI 1.1–1.6 in cross-section II). In con-
@M;(K<%h Table 1: Participant characteristics.
'"YYj$>
' 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*]$v 75–79 422 11.6 407 11.6
C".1
+Um 80–84 230 6.3 226 6.4
Ww9;UP'G 85–89 100 2.7 110 3.1
xF8S*,#,* 90+ 36 1.0 24 0.7
NP
t(MFK\ Female 2072 56.7 1998 57.0
H[&@}v,L Ever Smokers 1784 51.2 1789 51.2
Cn
h|D^{s Use of inhaled steroids 370 10.94 478 13.8^
Epjff@7A History of:
Lk,+Tfk" Diabetes 284 7.8 347 9.9^
]r"Yqv3 Hypertension 1669 46.0 1825 52.2^
H#(<-)j0_ Emmetropia* 1558 42.9 1478 42.2
QApyP CH Myopia* 442 12.2 495 14.1^
.XH8YT42 Hyperopia* 1633 45.0 1532 43.7
!k&)EWP? n = number of persons affected
Yv\!vW7I * best spherical equivalent refraction correction
x7ATI[b[ ^ P < 0.01
aC\4}i< BMC Ophthalmology 2006, 6:17
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!D:k! (page number not for citation purposes)
o0Gx%99' t
mnQ'X-q3iO rast, men had slightly higher PSC prevalence than women
9M2f!kJP$ 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
TmP8q
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,
DrS?=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.
$rB!Ex{@ac Cataract type Age (years) Cross-section I Cross-section II
LUul7y'" n % (95% CL)* n % (95% CL)*
%8<2> Cortical 50–54 473 4.4 (2.6–6.3) 338 7.4 (4.6–10.2)
RAOKZ~` 55–59 522 9.2 (6.7–11.7) 542 9.0 (6.6–11.5)
enPYj.*/0 60–64 615 16.4 (13.5–19.4) 556 16.7 (13.6–19.8)
J/[7d?hI/ 65–69 653 26.2 (22.8–29.6) 581 23.6 (20.1–27.0)
l#ygb|=x 70–74 516 31.2 (27.2–35.2) 514 35.4 (31.3–39.6)
+gNX7xuY 75–79 366 40.2 (35.1–45.2) 332 39.8 (34.5–45.1)
P2QRvn6v 80–84 194 58.8 (51.8–65.8) 163 42.9 (35.3–50.6)
H<z30r/-w 85–89 74 52.7 (41.1–64.4) 73 54.8 (43.1–66.5)
'tSnH&c 90+ 22 68.2 (47.0–89.3) 14 78.6 (54.0–103.2)
vVdxi9yk PSC 50–54 474 2.7 (1.3–4.2) 338 2.4 (0.7–4.0)
|i s 9 55–59 522 2.9 (1.4–4.3) 541 2.6 (1.3–3.9)
l3\9S#3-^ 60–64 616 4.6 (2.9–6.2) 548 5.7 (3.7–7.6)
*NF&Y 65–69 655 6.3 (4.4–8.1) 573 4.5 (2.8–6.3)
(I!1sE!?1 70–74 517 6.8 (4.6–8.9) 505 9.7 (7.1–12.3)
\`&xprqAw 75–79 367 11.4 (8.2–14.7) 327 9.5 (6.3–12.7)
Ga?UHw~ 80–84 196 12.2 (7.6–16.9) 155 10.3 (5.5–15.2)
1
3\Sh 85–89 74 18.9 (9.8–28.1) 69 11.6 (3.9–19.4)
uzO{{S- 90+ 23 21.7 (3.5–40.0) 11 0.0
k|fh\F+$ 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)
"3v7 gtGG 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.
uAC hu] 0
ZjE~W>pkQ 10
YHJ' 20
Mp!2`4rD 30
O^y$8OKEi, 40
}'%$7vL`Ft 50
CzK%x?~] cortical PSC nuclear any
(69kvA&|q cataract
x/pC%25 Cataract type
hU |LFjc %
)kFme=
; Cross-section I
0m
qSA Cross-section II
rD_Ss.\^g BMC Ophthalmology 2006, 6:17
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fN~8L}!l (page number not for citation purposes)
Z?vY3) prevalence of any cataract (including cataract surgery) was
}S
Y`KoC1 relatively stable over the 6-year period.
L2:oZ&:u`J Although different population-based studies used different
NHst7$Y< grading systems to assess cataract [15], the overall
Yk(NZ3O prevalence of the three cataract types were similar across
\UVT_=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
&