Operated and unoperated cataract in Australia

ABSTRACT
Purpose: To quantify the prevalence of cataract, the outcomes
of cataract surgery and the factors related to
unoperated cataract in Australia.
Methods: Participants were recruited from the Visual
Impairment Project: a cluster, stratified sample of more than
5000 Victorians aged 40 years and over. At examination
sites interviews, clinical examinations and lens photography
were performed. Cataract was defined in participants who
had: had previous cataract surgery, cortical cataract greater
than 4/16, nuclear greater than Wilmer standard 2, or
posterior subcapsular greater than 1 mm2.
Results: The participant group comprised 3271 Melbourne
residents, 403 Melbourne nursing home residents and 1473
rural residents.The weighted rate of any cataract in Victoria
was 21.5%. The overall weighted rate of prior cataract
surgery was 3.79%. Two hundred and forty-nine eyes had
had prior cataract surgery. Of these 249 procedures, 49
(20%) were aphakic, 6 (2.4%) had anterior chamber
intraocular lenses and 194 (78%) had posterior chamber
intraocular lenses.Two hundred and eleven of these operated
eyes (85%) had best-corrected visual acuity of 6/12 or
better, the legal requirement for a driver’s license.Twentyseven
(11%) had visual acuity of less than 6/18 (moderate
vision impairment). Complications of cataract surgery
caused reduced vision in four of the 27 eyes (15%), or 1.9%
of operated eyes. Three of these four eyes had undergone
intracapsular cataract extraction and the fourth eye had an
opaque posterior capsule. No one had bilateral vision
impairment as a result of cataract surgery. Surprisingly, no
particular demographic factors (such as age, gender, rural
residence, occupation, employment status, health insurance
status, ethnicity) were related to the presence of unoperated
cataract.
Conclusions: Although the overall prevalence of cataract is
quite high, no particular subgroup is systematically underserviced
in terms of cataract surgery. Overall, the results of
cataract surgery are very good, with the majority of eyes
achieving driving vision following cataract extraction.
Key words: cataract extraction, health planning, health
services accessibility, prevalence
INTRODUCTION
Cataract is the leading cause of blindness worldwide and, in
Australia, cataract extractions account for the majority of all
ophthalmic procedures.1 Over the period 1985–94, the rate
of cataract surgery in Australia was twice as high as would be
expected from the growth in the elderly population.1
Although there have been a number of studies reporting
the prevalence of cataract in various populations,2–6 there is
little information about determinants of cataract surgery in
the population. A previous survey of Australian ophthalmologists
showed that patient concern and lifestyle, rather
than visual acuity itself, are the primary factors for referral
for cataract surgery.7 This supports prior research which has
shown that visual acuity is not a strong predictor of need for
cataract surgery.8,9 Elsewhere, socioeconomic status has
been shown to be related to cataract surgery rates.10
To appropriately plan health care services, information is
needed about the prevalence of age-related cataract in the
community as well as the factors associated with cataract
surgery. The purpose of this study is to quantify the prevalence
of any cataract in Australia, to describe the factors
related to unoperated cataract in the community and to
describe the visual outcomes of cataract surgery.
METHODS
Study population
Details about the study methodology for the Visual
Impairment Project have been published previously.11
Briefly, cluster sampling within three strata was employed to
recruit subjects aged 40 years and over to participate.
Within the Melbourne Statistical Division, nine pairs of
census collector districts were randomly selected. Fourteen
nursing homes within a 5 km radius of these nine test sites
were randomly chosen to recruit nursing home residents.
Clinical and Experimental Ophthalmology (2000) 28, 77–82
Original Article
Operated and unoperated cataract in Australia
Catherine A McCarty PhD, MPH, Mukesh B Nanjan PhD, Hugh R Taylor MD
Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, Melbourne, Victoria, Australia
n Correspondence: Dr Cathy McCarty MPH, Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, 32 Gisborne Street, East Melbourne,
Victoria 3002, Australia. Email: cathy@cera.unimelb.edu.au
78 McCarty et al.
Finally, four pairs of census collector districts in four rural
Victorian communities were randomly selected to recruit rural
residents. A household census was conducted to identify
eligible residents aged 40 years and over who had been a
resident at that address for at least 6 months. At the time of
the household census, basic information about age, sex,
country of birth, language spoken at home, education, use of
corrective spectacles and use of eye care services was collected.
Eligible residents were then invited to attend a local
examination site for a more detailed interview and examination.
The study protocol was approved by the Royal Victorian
Eye and Ear Hospital Human Research Ethics Committee.
Assessment of cataract
A standardized ophthalmic examination was performed after
pupil dilatation with one drop of 10% phenylephrine
hydrochloride. Lens opacities were graded clinically at the
time of the examination and subsequently from photos using
the Wilmer cataract photo-grading system.12 Cortical and
posterior subcapsular (PSC) opacities were assessed on
retroillumination and measured as the proportion (in 1/16)
of pupil circumference occupied by opacity. For this analysis,
cortical cataract was defined as 4/16 or greater opacity,
PSC cataract was defined as opacity equal to or greater than
1 mm2 and nuclear cataract was defined as opacity equal to
or greater than Wilmer standard 2,12 independent of visual
acuity. Examples of the minimum opacities defined as cortical,
nuclear and PSC cataract are presented in Figure 1.
Bilateral congenital cataracts or cataracts secondary to
intraocular inflammation or trauma were excluded from the
analysis. Two cases of bilateral secondary cataract and eight
cases of bilateral congenital cataract were excluded from the
analyses.
A Topcon® SL5 photo slit-lamp (Topcon America Corp.,
Paramus, NJ, USA) with a 0.1 mm slit beam of 9.0 mm in
height set to an incident angle of 30° was used for examinations.
Ektachrome® 200 ASA colour slide film (Eastman
Kodak Company, Rochester, NY, USA) was used to photograph
the nuclear opacities. The cortical opacities were
photographed with an Oxford® retroillumination camera
(Marcher Enterprises Ltd, Hereford, UK) and T-MAX® 400
film (Eastman Kodak). Photographs were graded separately
by two research assistants and discrepancies were adjudicated
by an independent reviewer. Any discrepancies
between the clinical grades and the photograph grades were
resolved. Except in cases where photographs were missing,
the photograph grades were used in the analyses. Photograph
grades were available for 4301 (84%) for cortical
cataract, 4147 (81%) for nuclear cataract and 4303 (84%)
for PSC cataract. Cataract status was classified according to
the severity of the opacity in the worse eye.
Assessment of risk factors
A standardized questionnaire was used to obtain information
about education, employment and ethnic background.11
Specific information was elicited on the occurrence, duration
and treatment of a number of medical conditions,
including ocular trauma, arthritis, diabetes, gout, hypertension
and mental illness. Information about the use, dose and
duration of tobacco, alcohol, analgesics and steriods were
collected, and a food frequency questionnaire was used to
determine current consumption of dietary sources of antioxidants
and use of vitamin supplements.
Data management and statistical analysis
Data were collected either by direct computer entry with a
questionnaire programmed in Paradox© (Carel Corporation,
Ottawa, Canada) with internal consistency checks, or
on self-coding forms. Open-ended responses were coded at
a later time. Data that were entered on the self-coded forms
were entered into a computer with double data entry and
reconciliation of any inconsistencies. Data range and consistency
checks were performed on the entire data set.
SAS© version 6.1 (SAS Institute, Cary, North Carolina) was
employed for statistical analyses.
Ninety-five per cent confidence limits around the agespecific
rates were calculated according to Cochran13 to
account for the effect of the cluster sampling. Ninety-five
per cent confidence limits around age-standardized rates
were calculated according to Breslow and Day.14 The strataspecific
data were weighted according to the 1996
Australian Bureau of Statistics census data15 to reflect the
cataract prevalence in the entire Victorian population.
Univariate analyses with Student’s t-tests and chi-squared
tests were first employed to evaluate risk factors for unoperated
cataract. Any factors with P < 0.10 were then fitted
into a backwards stepwise logistic regression model. For the
Figure 1. Minimum levels of cortical (a), nuclear (b), and posterior subcapsular (c) cataract.
final multivariate models, P < 0.05 was considered statistically
significant. Design effect was assessed through the use
of cluster-specific models and multivariate models. The
design effect was assumed to be additive and an adjustment
made in the variance by adding the variance associated with
the design effect prior to constructing the 95% confidence
limits.
RESULTS
Study population
A total of 3271 (83%) of the Melbourne residents, 403
(90%) Melbourne nursing home residents, and 1473 (92%)
rural residents participated. In general, non-participants did
not differ from participants.16 The study population was
representative of the Victorian population and Australia as
a whole.
The Melbourne residents ranged in age from 40 to
98 years (mean = 59) and 1511 (46%) were male. The
Melbourne nursing home residents ranged in age from 46 to
101 years (mean = 82) and 85 (21%) were men. The rural
residents ranged in age from 40 to 103 years (mean = 60)
and 701 (47.5%) were men.
Prevalence of cataract and prior cataract surgery
As would be expected, the rate of any cataract increases
dramatically with age (Table 1). The weighted rate of any
cataract in Victoria was 21.5% (95% CL 18.1, 24.9).
Although the rates varied somewhat between the three
strata, they were not significantly different as the 95% confidence
limits overlapped. The per cent of cataractous eyes
with best-corrected visual acuity of less than 6/12 was 12.5%
(65/520) for cortical cataract, 18% for nuclear cataract
(97/534) and 14.4% (27/187) for PSC cataract. Cataract
surgery also rose dramatically with age. The overall
weighted rate of prior cataract surgery in Victoria was
3.79% (95% CL 2.97, 4.60) (Table 2).
Risk factors for unoperated cataract
Cases of cataract that had not been removed were classified
as unoperated cataract. Risk factor analyses for unoperated
cataract were not performed with the nursing home residents
as information about risk factor exposure was not
available for this cohort. The following factors were assessed
in relation to unoperated cataract: age, sex, residence
(urban/rural), language spoken at home (a measure of ethnic
integration), country of birth, parents’ country of birth (a
measure of ethnicity), years since migration, education, use
of ophthalmic services, use of optometric services, private
health insurance status, duration of distance glasses use,
glaucoma, age-related maculopathy and employment status.
In this cross sectional study it was not possible to assess the
level of visual acuity that would predict a patient’s having
cataract surgery, as visual acuity data prior to cataract
surgery were not available.
The significant risk factors for unoperated cataract in univariate
analyses were related to: whether a participant had
ever seen an optometrist, seen an ophthalmologist or been
diagnosed with glaucoma; and participants’ employment
status (currently employed) and age. These significant
factors were placed in a backwards stepwise logistic regression
model. The factors that remained significantly related
to unoperated cataract were whether participants had ever
seen an ophthalmologist, seen an optometrist and been
diagnosed with glaucoma. None of the demographic factors
were associated with unoperated cataract in the multivariate
model.
The per cent of participants with unoperated cataract
who said that they were dissatisfied or very dissatisfied with
Operated and unoperated cataract in Australia 79
Table 1. Prevalence of any cataracta (excluding previous cataract surgery) by age, gender and cohort
Age group Sex Urban Rural Nursing home Weighted total
(years) (%) (%) (%)
40–49 Male 2.56 4.04 0.00 3.00 (1.91, 4.08)
Female 2.61 1.70 0.00 2.36 (1.61, 3.10)
50–59 Male 7.69 6.94 0.00 7.47 (5.80, 9.15)
Female 6.67 7.56 0.00 6.92 (5.60, 8.24)
60–69 Male 20.7 25.0 10.0 22.0 (18.1, 26.0)
Female 27.9 35.7 37.5 30.3 (26.0, 34.7)
70–79 Male 43.1 58.7 39.1 48.1 (41.2, 55.1)
Female 58.6 66.2 55.6 61.0 (56.0, 65.9)
80–89 Male 74.0 89.3 92.0 79.3 (72.3, 86.3)
Female 91.9 97.0 80.2 92.6 (86.4, 98.8)
90 + Male 100.0 100.0 75.0 98.8 (96.2, 100.0)
Female 100.0 100.0 93.8 98.6 (97.0, 100.0)
Age-standardized
(95% CL) Combined 19.7 (16.3, 23.1) 23.2 (16.1, 30.2) 16.5 (2.06, 30.9) 21.5 (18.1, 25.0)
aCortical > 4/16, nuclear > standard 2, posterior subcapsular > 1 mm2
their current vision was 30% (290/683), compared with 27%
(26/95) of participants with prior cataract surgery (chisquared,
1 d.f. = 0.25, P = 0.62).
Outcomes of cataract surgery
Two hundred and forty-nine eyes had undergone prior
cataract surgery. Of these 249 operated eyes, 49 (20%) were
left aphakic, 6 (2.4%) had anterior chamber intraocular
lenses and 194 (78%) had posterior chamber intraocular
lenses. The rate of capsulotomy in the eyes with intact
posterior capsules was 36% (73/202). Fifteen per cent of
eyes (17/114) with a clear posterior capsule had bestcorrected
visual acuity of less than 6/12 compared with 43%
of eyes (6/14) with opaque capsules, and 15% of eyes
(11/73) with prior capsulotomies (chi-squared, 2 d.f. = 7.21,
P = 0.027).
The percentage of eyes with best-corrected visual acuity
of 6/12 or better was 96% (302/314) for eyes without
cataract, 88% (1417/1609) for eyes with prevalent cataract
and 85% (211/249) for eyes with operated cataract (chisquared,
2 d.f. = 22.3), P < 0.001). Twenty-seven of the
operated eyes (11%) had visual acuities of less than 6/18
(moderate vision impairment) (Fig. 2). A cause of this
moderate visual impairment (but not the only cause) in four
(15%) eyes was secondary to cataract surgery. Three of these
four eyes had undergone intracapsular cataract extraction
and the fourth eye had an opaque posterior capsule. No one
had bilateral vision impairment as a result of their cataract
surgery.
DISCUSSION
To our knowledge, this is the first paper to systematically
assess the prevalence of current cataract, previous cataract
surgery, predictors of unoperated cataract and the outcomes
of cataract surgery in a population-based sample. The Visual
Impairment Project is unique in that the sampling frame and
high response rate have ensured that the study population is
representative of Australians aged 40 years and over. Therefore,
these data can be used to plan age-related cataract
services throughout Australia.
We found the rate of any cataract in those over the age
of 40 years to be 22%. Although relatively high, this rate is
significantly less than was reported in a number of previous
studies,2,4,6 with the exception of the Casteldaccia Eye
Study.5 However, it is difficult to compare rates of cataract
between studies because of different methodologies and
cataract definitions employed in the various studies, as well
as the different age structures of the study populations.
Other studies have used less conservative definitions of
cataract, thus leading to higher rates of cataract as defined.
In most large epidemiologic studies of cataract, visual acuity
has not been included in the definition of cataract.
Therefore, the prevalence of cataract may not reflect the
actual need for cataract surgery in the community.
80 McCarty et al.
Table 2. Prevalence of previous cataract by age, gender and cohort
Age group Gender Urban Rural Nursing home Weighted total
(years) (%) (%) (%)
40–49 Male 1.14 0.00 0.00 0.80 (0.00, 1.81)
Female 0.00 0.00 0.00 0.00 (
50–59 Male 0.68 0.58 0.00 0.65 (0.13, 1.17)
Female 0.57 0.00 0.00 0.41 (0.00, 1.00)
60–69 Male 2.12 7.59 0.00 3.80 (1.41, 6.19)
Female 2.11 3.51 0.00 2.54 (1.81, 3.26)
70–79 Male 8.22 9.85 8.70 8.75 (6.38, 11.1)
Female 7.21 7.86 7.02 7.41 (5.36, 9.46)
80–89 Male 25.0 30.0 14.3 26.2 (17.0, 35.4)
Female 27.9 25.6 18.3 26.7 (20.2, 33.3)
90 + Male 0.00 16.7 66.7 9.19 (0.00, 21.5)
Female 58.3 100.0 26.9 63.1 (44.4, 81.8)
Age-standardized
(95% CL) Combined 3.31 (2.70, 3.93) 4.36 (2.67, 6.06) 2.26 (0.82, 3.70) 3.79 (2.97, 4.60)
Figure 2. Visual acuity in eyes that had undergone cataract
surgery, n = 249. h, Presenting; j, best-corrected.
Operated and unoperated cataract in Australia 81
The weighted prevalence of prior cataract surgery in the
Visual Impairment Project (3.6%) was similar to the crude
rate in the Beaver Dam Eye Study4 (3.1%), but less than the
crude rate in the Blue Mountains Eye Study6 (6.0%).
However, the age-standardized rate in the Blue Mountains
Eye Study (standardized to the age distribution of the urban
Visual Impairment Project cohort) was found to be less than
the Visual Impairment Project (standardized rate = 1.36%,
95% CL 1.25, 1.47). The incidence of cataract surgery in
Australia has exceeded population growth.1 This is due,
perhaps, to advances in surgical techniques and lens
implants that have changed the risk–benefit ratio.
The Global Initiative for the Elimination of Avoidable
Blindness, sponsored by the World Health Organization,
states that cataract surgical services should be provided that
‘have a high success rate in terms of visual outcome and
improved quality of life’,17 although the ‘high success rate’ is
not defined. Population- and clinic-based studies conducted
in the United States have demonstrated marked improvement
in visual acuity following cataract surgery.18–20 We
found that 85% of eyes that had undergone cataract extraction
had visual acuity of 6/12 or better. Previously, we have
shown that participants with prevalent cataract in this
cohort are more likely to express dissatisfaction with their
current vision than participants without cataract or participants
with prior cataract surgery.21 In a national study in the
United States, researchers found that the change in patients’
ratings of their vision difficulties and satisfaction with their
vision after cataract surgery were more highly related to
their change in visual functioning score than to their change
in visual acuity.19 Furthermore, improvement in visual function
has been shown to be associated with improvement in
overall quality of life.22
A recent review found that the incidence of visually
significant posterior capsule opacification following
cataract surgery to be greater than 25%.23 We found 36%
capsulotomy in our population and that this was associated
with visual acuity similar to that of eyes with a clear
capsule, but significantly better than that of eyes with an
opaque capsule.
A number of studies have shown that the demand and
timing of cataract surgery vary according to visual acuity,
degree of handicap and socioeconomic factors.8–10,24,25 We
have also shown previously that ophthalmologists are more
likely to refer a patient for cataract surgery if the patient is
employed and less likely to refer a nursing home resident.7
In the Visual Impairment Project, we did not find that any
particular subgroup of the population was at greater risk of
having unoperated cataract. Universal access to health care
in Australia may explain the fact that people without
Medicare are more likely to delay cataract operations in the
USA,8 but not having private health insurance is not associated
with unoperated cataract in Australia.
In summary, cataract is a significant public health problem
in that one in four people in their 80s will have had cataract
surgery. The importance of age-related cataract surgery will
increase further with the ageing of the population: the
number of people over age 60 years is expected to double in
the next 20 years. Cataract surgery services are well
accessed by the Victorian population and the visual outcomes
of cataract surgery have been shown to be very good.
These data can be used to plan for age-related cataract
surgical services in Australia in the future as the need for
cataract extractions increases.
ACKNOWLEDGEMENTS
The Visual Impairment Project was funded in part by grants
from the Victorian Health Promotion Foundation, the
National Health and Medical Research Council, the Ansell
Ophthalmology Foundation, the Dorothy Edols Estate and
the Jack Brockhoff Foundation. Dr McCarty is the recipient
of a Wagstaff Fellowship in Ophthalmology from the Royal
Victorian Eye and Ear Hospital.
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