Ophthalmic Epidemiology, 14:408–414ISSN: 0928-6586 print / 1744-5086 onlineCopyright c© 2007 Informa Healthcare USA, Inc.DOI: 10.1080/09286580701316124

Australian Prospective Study of Cataract Surgeryand Age-Related Macular Degeneration:

Rationale and MethodologySudha Cugati,1 Tania de Loryn,1 Thuan Pham,1 Jennifer Arnold,2 Paul Mitchell,1 and Jie Jin Wang1

1Centre for Vision Research, Department of Ophthalmology and the Westmead Millennium Institute, University of Sydney, Sydney, Australia2Marsden Eye Specialists, Parramatta, NSW Australia

ABSTRACT

Background: Cataract surgery is the most frequently performed ophthalmic procedureworldwide. While benefits gained from cataract surgery outweigh surgical risks, there havebeen concerns that older persons may have an increased risk of developing age-relatedmacular degeneration (AMD) after cataract surgery. Objective: The Australian ProspectiveStudy of Cataract Surgery and Age-Related Macular Degeneration Study aims to assessthe risk of AMD in a large cohort of older patients following cataract surgery. The currentreport describes the study rationale, design and methodology. Design: Longitudinal studyParticipants: Approximately 2000 cataract surgical patients aged 65 years or older are beingrecruited from both public and private sources in western Sydney, Australia. Methods: At studyvisits, participants are interviewed using standardized questionnaires to obtain informationon demographic, medical, and ocular conditions and AMD risk factors, together with data ongeneral health and vision-related quality of life. Eye examinations include visual acuity, in-traocular pressure, keratometry and A-scan measurements, plus lens and retinal photography,following pupil dilatation. Retinal photographs taken before cataract surgery, and at 1, 6, 12,and 24 months after surgery are graded for early and late AMD lesions, using the Wisconsinage-related maculopathy grading system. The 1-month post-operative retinal photographssupplement the baseline macular assessment for cases in which cataract occludes a clearview of the macula pre-operatively. It is intended that study participants will be followed forup to five years post-operatively to clarify the question of whether aphakic or pseudophakic,compared to phakic eyes, have a greater risk of developing AMD.

INTRODUCTION

Cataract surgery is currently among the most frequently per-formed surgical procedures in medicine, and is arguably the mostcost-effective.1−6 In Australia, the estimated annual increase incataract surgical procedures is 5.5%7 and the average annualincrease in prevalent cataract surgery in older populations is5.6%.8 These increases are likely the result of population agingcombined with current trends towards earlier surgery3 and an

Received 22 December 2006; Accepted 26 February 2007.Keywords: Cataract surgery, AMD, blindnessCorrespondence to:Jie Jin WangCentre for Vision ResearchDepartment of OphthalmologyUniversity of SydneyWestmead HospitalHawkesbury Road, Westmead NSW 2145, Australiaemail: jiejin wang@wmi.usyd.edu.au

increase in second eye surgery.8 It has been estimated that 2.74million Australians aged over 50 years will have cataract in ei-ther eye by the year 2021,9 thus a further increase in cataractsurgery is anticipated.

While cataract is the major cause of mild visual impairmentin older persons, age-related macular degeneration (AMD) isthe major cause of moderate to severe visual impairment.10,11

Although both conditions are associated with age, there is noconsistent evidence to suggest that the two conditions (cataractand AMD) are directly related or that they share the sameetiology.12−15 Ophthalmologists have long been concerned,however, with the possibility that cataract surgical eyes may bemore prone to develop AMD.16−24 While the benefits of cataractsurgery clearly outweigh surgical risks,25−34 this long-term po-tential adverse outcome deserves clarification.

STUDY RATIONALE AND HYPOTHESIS

A number of clinical case series reports,16−35 published in the1960s and 1970s, suggested a link between AMD and cataract

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surgery. Another report,36 in which eyes were examined post-mortem, suggested that neovascular AMD was more frequentlyobserved in pseudophakic than phakic eyes. These reports, how-ever, gave no indication as to whether there may have been sub-tle new vessels, which existed but were unrecognized, prior tosurgery.

Pollack et al.12,18 reported findings from 47 patients with bi-lateral symmetric early AMD. Each patient had only one eyeoperated upon, with the second acting as a control. Fluoresceinangiography was performed pre- and post-operatively. The au-thors documented an increased risk of AMD in operated eyessix to twelve months following cataract surgery. In a clinicalfollow-up study, Armbrecht et al.,33,37 however, was unableto find an association between cataract surgery and AMD, bycomparing patients with AMD who either underwent cataractsurgery or had no surgery. The shortcomings of these clinicalstudies have kept this longstanding question unresolved. Thesmall numbers in these case series were also likely to be subjectto selection bias. Further, there was no randomization proce-dure to decide which patient, or which eye, should be operatedupon and the doctors’ decision could have been biased towardsthe eye or the patient with worse vision. We therefore do notknow how comparable the operated and the non-operated groupswere.

Only recently have population-based studies begun to addressthis question. To date, findings from population-based epidemi-ological cross-sectional and longitudinal studies have been rel-atively consistent (Table 1). Pooled cross-sectional data fromthe Salisbury Eye Evaluation Project, the Proyecto VER and theBaltimore Eye Survey21 support an association between priorcataract surgery and an increased prevalence of AMD five ormore years post-surgery.

Longitudinal data from the Beaver Dam Eye Study have alsoconsistently shown a link between prior cataract surgery andthe five-year22 and ten-year incidence of AMD.23 Pseudophakic

Table 1. Results of major studies reporting on the possible risk of age-related macular degeneration (AMD) following cataract surgery)

Author, year Number ofof publication Design of study eyes Final result∗ Potential weakness

Klein R et al.[401], Cross sectional (population- 341 Increased odds of early AMD in aphakic/ Residual confounding?1994 based) pseudophakic eyes (OR 1.59; 95% CI,

1.15–2.19)Wang J. J. Cross sectional (population- 304 No relationship was found between previous Residual confounding?

et al.[26638], 1999 based) cataract surgery and early or late AMD.Freeman EE Cross sectional (combined 999 Increased prevalence of late AMD in eyes after Residual confounding?

et al.[34368], 2003 analysis from 3 population- cataract surgery (OR 1.7; 95% CI, 1.1–2.6)based cohorts)

Klein R et al.[21116], Longitudinal (population- 235 Increased risk of late AMD in eyes 5 years after Small numbers of incident1998 based) cataract surgery (RR, 2.8; 95% CI, 1.03–7.63) late AMD cases

Klein R et al. [30232], Longitudinal (population- 233 Increased risk of late AMD in eyes 10 years after Small numbers of incident2002 based) cataract surgery (RR, 3.81; 95% CI, 1.89–7.69) late AMD cases

Wang J. J. et al.[32260], Longitudinal (combined 315 Increased risk of late stage AMD in eyes 5 years Small numbers of incident2003 analysis from 2 population- after cataract surgery (RR, 3.1; 95% CI, 1.7–5.9) late AMD cases

based cohorts)

∗OR: Odds ratio; RR: Relative risk; CI: Confidence interval.

eyes were found to be four times more likely to develop AMDthan phakic eyes. There remains a question as to whether eyeswith ARD were more likely to be operated upon. Data fromthe Beaver Dam Eye Study, however, could not confirm thatthe presence of ARD lesions was related to incident cataractsurgery.38

Pooled longitudinal data from the Beaver Dam Eye Study andBlue Mountains Eye Study (BMES)24 have, so far, provided thestrongest evidence supporting a long-term (five or more years)association between cataract surgery and risk of AMD. Bothstudies followed similar study protocols and diagnosed AMDfrom retinal photographic grading. All incident AMD cases wereconfirmed using side-by-side grading and cross-validated by in-vestigators. Subject-specific and eye-specific data were analyzedto test for consistency of the findings. The age-adjusted relativerisk was around 4.0, a magnitude stronger than the reportedmagnitude of the association between smoking and incidentAMD.

After multivariable adjustment, the increased odds were be-tween three to five-fold for cataract surgical eyes compared tophakic eyes. Higher odds were observed in models after fur-ther adjusting for the level of baseline early AMD, suggestingthat cataract surgical eyes developing late AMD did not have asmuch advanced early AMD as phakic eyes that developed lateAMD.

Possible explanations for the association between cataractsurgery and AMD incidence may include the following:

1) a link between cataract and AMD incidence2) shared risk factors between cataract and AMD and,3) acceleration of the progression from early to late stage

AMD due to the post-operative ocular environment.

There is also a possibility that only a sub-group of the popu-lation (Caucasians or those presenting with early stage lesions),

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Table 2. Sample size and smallest relative risks (RR) detectable for 2-year incident age-related maculardegeneration (AMD) lesions in persons aged over 65 years (case: control = 1:1)

AMD incidence 90% follow-up rate 80% follow-up rate5-year∗ % 2-year % Sample size Smallest RR Sample size Smallest RR

Neovascular AMD 1.13 0.45 1645 3.1 1472 3.3Geographic atrophy 0.92 0.37 1645 3.4 1472 3.6Either AMD lesion 1.86 0.74 1645 2.5 1472 2.7

∗Based on combined analysis of the Beaver Dam and Blue Mountains Eye Studies[32260].

who are already at higher risk of developing AMD, may havean increased risk of developing this condition following cataractsurgery.

Previous large-scale cataract surgical outcome studies39,40

did not specifically evaluate the risk of AMD following cataractsurgery. There is a need for large, long-term prospective cohortstudies, with careful documentation of the macular conditionprior to and following surgery. The current report outlines sucha large cohort study of cataract surgical patients. In this project,we aim to clarify this important longstanding clinical question inorder to improve the quality of eye care delivery and to maximizesurgical benefits. If the link between prior cataract surgery andan increased risk of subsequent progression to late AMD wereconfirmed, it would have significant implications.

Clinicians may need to provide informed consent about thisrisk before indicating the need for cataract surgery and may needto revisit the timing of cataract surgery for patients with signssuggesting a high risk of progression to late AMD, who still havemanageable visual function. Clinicians may need to emphasizevigilance in presenting quickly should any visual symptoms de-velop in surgical patients to enhance the potential for timelylaser or other late AMD therapies. Other approaches could in-clude closer follow-up of at-risk patients post-operatively. Thisstudy may motivate researchers to investigate other AMD risksrelated to cataract surgery, such as inflammation, type of in-traocular lens used, light exposure during and after cataractsurgery.

MATERIALS AND METHODS

Study aims

The project is a longitudinal follow-up of patients aged65 years or older, who are undergoing cataract surgery at theWestern Sydney Eye Hospital or at private ophthalmic practicesin the Western Sydney region. The aim of the study is to evalu-ate the risk of developing AMD after cataract surgery in a largecohort of older patients, taking into account the pre-operativeappearance of the macula of both eyes and known AMD riskfactors.

Study sample

Sample size calculations were based on the 5-year incidenceof late AMD estimated using population-based data from the

Blue Mountains Eye Study. Over 3 years, 2000 patients will berecruited and followed after surgery annually for up to 5 years.Estimating a 2-year mortality of 8.6% (n = 172),41 and with 80–90% retention rate by 2 years, we expect to have around 1500participants with data available for analysis of the short-termrisk of AMD, two years after the surgery.

The smallest detectable relative risks based on the proposedsample size and assumed follow-up rates are shown in Table2. Previous studies suggested a 3- to 4-fold risk of develop-ing AMD over 5 or more years following cataract surgery.23,24

We anticipate that the proposed sample size will have sufficientpower to detect a 3-fold risk of incident late stage AMD ineyes after cataract surgery. This relative risk would be clinicallysignificant, if confirmed, to warrant a modification in clinicalpractice.

Patients aged 65 years and older undergoing cataract surgeryin the Western Sydney region at either the Western Sydney EyeHospital or at selected private ophthalmic rooms will be eligibleto participate in the study. Apart from age and evidence of lateAMD in the surgical eye, there are no other exclusion criteria.Patients are currently recruited either at the hospital or privateclinics when booked for cataract surgery, and written consent isobtained at that time.

Examinations and interview

All potential participants are interviewed and examined in astandardized manner. The process of gaining written informedconsent, questionnaire administration, clinical examination andretinal photography takes between 40 and 60 minutes.

Demographic data including ethnicity and contact details ofparticipants and their relatives are obtained during interview.Residents in the Western Sydney area have relatively diverseethnicity, and so do the study participants. Past medical his-tories including systemic and ocular conditions are recorded.Questions pertaining to AMD include any previous diagnosisof AMD and its treatment, AMD family history and smokingstatus. Questions relating to AMD and its treatment are val-idated from the clinical notes of the participant. In the eventthat we had no previous notes relating to the treatment, anattempt is made to contact the participants’ treating retinal physi-cian.

Participants who ever smoked are asked in detail to describethe type (cigarettes, hand rolled, cigars, or pipe) and how muchis usually smoked weekly, the age when smoking commenced,

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and when it stopped, or if participants were still smoking. Ques-tions relating to past medical history include diabetes, hyper-tension, angina, myocardial infarction, hyper-cholesterolemia,stroke or transient ischemic attack, arthritis, and surgical proce-dures. Details of systemic or ocular medications currently usedby the participant are recorded. The VF-14 questionnaire,42,43

Short-Form 36 questionnaire44 and a multidimensional func-tional assessment questionnaire45 were either interviewer- orself-administrated by each patient.

Prior to the eye evaluation, height and weight are recorded.Iris and skin colors are assessed by the examiner. Clinicalexamination includes the following:

a. Visual acuity (VA) is assessed using a logarithm ofthe minimum angle of resolution (Log MAR) visualacuity chart. The chart is retro-illuminated with auto-matic calibration to 85 cd/m2 (Vectorvision CSV-1000,Vectorvision, Inc, Dayton, OH) and read at 2.44 m (8 ft).VA is assessed initially with current glasses, if worn,then using a pinhole aperture. If no letters can be read at2.44 m (8 ft), the VA is assessed as counting fingers at0.61 m (2 ft), hand movements, perception of light or noperception of light.46 For participants who are illiterateor non-English speaking, vision is assessed using an “E”chart.

b. Intraocular pressure (IOP) using a Goldmann applana-tion tonometer.

c. Keratometry using the Topcon OM4 keratometerd. A- scan using Sonomed A 1500 for determining intraoc-

ular lens power.e. Lens and retinal photography of both eyes after pupil di-

latation using 1.0% tropicamide and 10% phenylephrine,using either a Topcon TRC 50 IA retinal camera withKodachrome 64 35 mm slide film, a Canon CR-45 NMnon-mydriatic camera (for participants who refuse pupildilatation) and a Canon CF-60DSi mydriatic digital cam-era. In a subgroup of participants we performed gradingon both film-based and digital images. Intra grader reli-ability using the two types of images will be assessed.Stereo photographs taken of each eye center on the mac-ula (Diabetic Retinopathy Study field 2)47 and the opticdisc (field 1). For diabetic participants, non-stereo pho-tographs that include part of the optic disc48,49 are takenof Diabetic Retinopathy Study fields 3 (temporal), 4 and5 (upper and lower temporal vascular arcades) and a fieldnasal to, but including, part of the optic disc. If partic-ipants are found to have suspected neovascular AMD,fluorescein angiography is performed with an immedi-ate referral to a local retinal specialist for confirmationand consideration of treatment.

Almost all cataract surgery procedures performed are pha-coemulsification with intraocular lens implant. Details of thesurgical procedure including duration of the phacoemulsifica-tion, total surgical time, surgical complications and type andpower of intraocular lens implanted are recorded.

Post-operative follow-up

Participants are followed post-operatively at 1 and 6 months,1, 2, 3, 4, and 5 years. At each follow-up visit, the same ex-amination and interview procedures are repeated, except for the1-month post-operative visit, when only retinal photography isrepeated to supplement the pre-operative macular assessment.

All participants are encouraged to attend each follow-up visit.In the event that a visit is missed, he/she is telephoned twice and,if this avenue fails, a letter is sent to encourage attendance. Insituations where transportation is an obstacle to participants’attending, free transport is provided. In situations when the par-ticipant attends the hospital eye clinic for other reasons, teammembers will use the opportunity to have the participant re-interviewed and re-examined for the study as well.

Study outcomes

Early and late AMD lesions are graded following methodsused in the BMES,50 a modification of the Wisconsin Age-Related Maculopathy (ARM) Grading System51 and lesions def-inition defined by the International Classification System forARM and AMD.52 AMD is classified as either early (presenceof soft indistinct or reticular drusen or the presence of bothsoft distinct drusen and RPE abnormalities within the maculararea) or late stage (neovascular AMD or geographic atrophy). IfAMD lesions are detected at the 1-month post-operative visit,they will be considered to have been present pre-operatively,unless having signs indicating that they are likely to be veryrecent, and these subjects will be excluded from the incidentcases. Eyes with ungradable photographs due to dense cataractwill be re-assessed at the 1 month post-operative visit, and theretinal appearance at this visit will be considered the baseline(pre-operative) appearance. As we take retinal photographs atmultiple visits, the number of participants with ungradable pho-tographs will be minimized. One photographic grader will gradeall retinal photographs using a masked manner. This photo-graphic grader was trained in the Wisconsin Grading Centerand has graded for AMD on a majority of the baseline pho-tographs and nearly all follow-up photographs taken from theBMES participants. Inter- and Intra-grader reliability was as-sessed previously in the BMES and was relatively high.50 Intra-grader reliability in this study will also be assessed.

If any new AMD lesions are detected in the surgical and non-surgical eyes, a side-by-side grading of the pre-operative and allpost-operative photographs will be performed, with adjudicationprovided by a senior researcher (JJW) and a retinal specialist(PM). All incident late AMD cases will be adjudicated. Theprimary outcome of the study will be the development of earlyor late AMD. The progression of early AMD lesions will alsobe assessed.

Statistical analysis

Statistical analysis will be performed using SAS (version 9.1,SAS Institute, Cary, NC). While a comparison of the cataractsurgical eyes with fellow phakic eyes as controls would be ideal,we are unable to limit study participants to have surgery in only

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one eye because of ethical concerns. Some participants havealready had their first eye operated at the time of recruitment(i.e. the second eye is the study eye), and others may have hadcataract surgery in their second eye during the follow-up periodof the study. As a result, the comparison of AMD incidence willbe made in following manner:

1) For participants who still have had only one eye oper-ated by the time of their follow-up visit (say at 12- or24-months), a paired comparison will be made, if thenumbers are sufficient;

2) Eye-specific analyses will be conduced to compare theincidence of AMD and major AMD lesions betweenpseudophakic and phakic eyes of this surgical cohort,while adjusting for the correlation between eyes;

3) Subject-specific analyses will be conducted to comparethe incidence of AMD and major AMD lesions betweenparticipants of this surgical cohort and age-sex matchedcontrols from a general older population, the BMESpopulation.

Chi-square statistics will be used to compare proportions.Logistic regression analysis will be used to assess the risk of de-veloping AMD in this surgical cohort compared to the risk foundin the general population after adjusting for age, sex, smoking,family history of AMD, and other potential AMD risk factors,if found significantly associated with AMD incidence. As pha-coemulsification power used during surgery, duration of surgery,and post-operative complications may be associated with the riskof developing AMD, we will evaluate the associations betweenthese operating factors and AMD incidence. Generalized esti-mating equation (GEE) models will be used for eye-specific dataanalysis. Change in health related quality of life after cataractsurgery would also be assessed.

Limitation of the study

Although a randomized control trial is an ideal study designto answer our study question of whether cataract surgery leadsto a higher risk of developing late AMD, there are potential eth-ical concerns if we were to randomize patients to a non-surgerygroup, when this was clinically needed. We have chosen a cohortstudy design to address our study question, but we are fully awareof the major limitation of cohort studies compared to randomizedcontrol trials, i.e., that intervention is not randomly allocated. Inan attempt to minimize this limitation in our study, we are care-fully documenting all macular conditions prior to surgery andshortly after surgery using retinal photography. This enables usto adjust for the presence of pre-operative early AMD lesionsin our statistical model. Such a modeling technique allows us toassess the risk of developing late AMD, assuming that both eyes(surgical and non-surgical) had the same level of early AMDpre-operatively.

PROGRESS TO DATE

Recruitment of study participants commenced in May 2004.To date, around 1,600 participants have been recruited, of whom

almost 70% have had surgery and attended the one-month visit.The remaining participants are on a waiting list for cataractsurgery. More women than men had cataract surgery (1.4:1.0).The mean age of participants who underwent cataract surgerywas 75.3 years (64–96 years) in women and 74.6 years (64–94years) in men. Among participants recruited, the distributionof ethnicity is as follows: European Caucasian (67.7%), Mid-dle Eastern (11.5%), East Asian (10.9%), South Asian (Indian)(5.2%), others or mixed race (3.7%). We assessed diagnosticagreement between the grading performed on pre-operative pho-tographs and the grading performed on 1-month post-operativephotographs. In a sub-sample of 260 participants with bothpre- and post-operative retinal photographs taken and grad-able, the diagnostic agreement for early AMD was around 70%(kappa = 0.7055), indicating the importance of 1-month post-operative photography to improve diagnostic accuracy. Therewere an insufficient number of late AMD cases to assessdiagnostic agreement.

POTENTIAL SIGNIFICANCE OF THE STUDY

Confirmation of a greater risk of incident AMD in eyes fol-lowing cataract surgery than in non-surgical eyes, would leadto a number of important outcomes. Firstly, this informationcould improve our understanding of the pathogenesis of AMDand may lead to further research to elucidate the mechanismby which cataract surgery triggers progression (e.g. inflamma-tory or other factors).53,54 This carries the potential for futurepharmacological prophylaxis for at-risk patients. It could alsoindicate a need for ophthalmologists to discuss AMD risk whenconsenting patients for cataract surgery, and may lead to a recom-mendation for delay in surgery in sub-groups of patients at highrisk of AMD but with reasonable visual acuity to function daily.

A practical outcome would be that at-risk patients are warnedto present quickly if any neovascular AMD symptoms develop(e.g., distortion of straight lines, a dark or grayish patch in thecentral visual field or sudden worsening of vision). This couldenhance the possibility of timely laser treatment (either usingconventional or photodynamic therapy). Other post-operativestrategies include close monitoring of at-risk patients to maxi-mize the benefit and minimize small, but important, risks fromcataract surgery.

As de Jong and Lubsen55 has rightly commented, that unlessreliable data are reported to deny this hypothesis, indicationsfor cataract surgery may need to become more stringent than ascurrently practiced by most ophthalmologists, at least for pa-tients who have signs indicating a high risk of progression tolate stage AMD.

ACKNOWLEDGMENTS

The study is supported by the Australian National Healthand Medical Research Council, Canberra Australia (Grant Nos:302010, 358702), and a Retina Australia 2005 research grant.

We wish to acknowledge the staff of the pre-admissionclinic and the eye clinic at Westmead Hospital for their

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support during the recruitment of participants for thestudy.

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