This study has provided age specific rates for 5 year incident cataract surgery in a representative older Australian urban community. Our study found similar age specific incidence to that reported from the comparable United States rural community of Beaver Dam, Wisconsin. Both communities had ready access to ophthalmic care; a single ophthalmologist practised full time in Beaver Dam, while in our region two ophthalmologists attended on a part-time basis.
In both studies, in both women and men, and for the three principal cataract types, increasing age was the most important predictor of incident cataract surgery.8
Cataract reflects well described ageing processes in the lens. Our prevalence data12
indicated that by the age of 80 years, 80% of participants either had significant cataract present in one or both eyes or had undergone cataract surgery.
Our study confirms previous clinical studies indicating that the presence of any PSC cataract at baseline is a highly significant ocular predictor of incident cataract surgery.8
This may be because PSC cataract causes a significantly greater drop in reading acuity and may increase glare sensitivity more than other types of cataract. In younger patients with PSC cataract who may be still working, uncorrected presbyopia in conjunction with PSC cataract may combine to result in a greater effect on reading vision and may be perceived as a more significant impediment than among patients in older age groups.
Participants with any nuclear cataract at baseline included the highest number of cataract surgical cases, which partly reflects the much higher nuclear cataract prevalence than PSC cataract. Among non-mixed cataracts, however, PSC cataract remained the strongest predictor of cataract surgery, followed by nuclear and cortical cataract.
Women had a higher age adjusted 5 year incidence of cataract surgery in either eye as well as in first or both eyes. Although not statistically significant in our study, this trend was mirrored and was statistically significant in the BDES. It may reflect either differences in cataract prevalence11,12,21–23
between men and women or alternatively it could reflect a tendency for women to access health services earlier than men.
As expected, visual impairment at the baseline examination was a very strong predictor of incident cataract surgery during the 5 year follow up period. We were not able to measure the extent to which advice from the study investigators about the presence of cataract at the time of the baseline examinations may have influenced the rate of cataract surgery thereafter. Although it is likely that such information could have increased the cataract surgical rate, our advice regarding any need for surgery was extremely conservative and participants were asked to discuss any relevant findings in our report with their general practitioner. This bias could have led to a somewhat higher rate of cataract surgery in our study population than in a comparable general population. We did not, however, provide any referrals for consideration of cataract surgery
The presence of myopia at the baseline examination was also a significant risk for cataract surgery. This may reflect either a biological association between myopia and the development or progression of cataract or to the myopic shift well known to accompany the development of nuclear sclerosis. More frequent eye examinations because of refractive needs could also contribute to higher cataract surgery rates, together with the increasing practice of clear lens extraction for refractive purposes.
In some studies, lower socioeconomic status has been associated with higher prevalence of cataract and with lower incidence of cataract surgery. We recently reported these data from our cohort and found no significant socioeconomic predictors of incident cataract surgery.24
A strength of our study lies in its population based sampling frame that reduces bias in patient selection. Our findings, however, did not include people too sick or weak to attend the follow up study. A number of studies,25–29
including our own,30
have demonstrated that the presence of cataract or cataract extraction may be a risk factor for mortality. Thus, it is also possible that those who did not attend because of poor health may have had a higher rate of incident cataract and cataract surgery, so that we could have underestimated the true rate.
The use of identical methodologies in the BMES and the BDES has permitted a close comparison of incident cataract surgery findings between these two large studies. Although the BDES age specific rates for cataract surgery were higher than in the BMES, the age adjusted rates were closer, taking into account the presence of associated cataract (Table 2) and other ocular characteristics (Table 4). The ocular factors found to predict incident cataract surgery were also relatively similar between these two studies, as was the magnitude of increased risk associated with presence of individual types of baseline cataract.
The largest difference between the two studies was the impact of baseline nuclear cataract, which led to a substantially higher risk of incident surgery in the BDES than in our study, either alone or in combination with other cataract types. This could reflect the higher nuclear cataract prevalence reported from our study than in the BDES.12
It could possibly also have been influenced by the random underexposure of around 30% of the nuclear cataract images in our baseline study, that we have previously discussed.12,31
The relative consistency in findings between the BMES and the BDES lends support to the findings from both studies. Although not formally tested, these data also suggest that the Wisconsin cataract grading system is likely to have reasonable interstudy reproducibility. Reliability within our own study has previously been documented.19
There are important limitations in any attempt to extrapolate our findings to other communities. Both the BMES and BDES samples are largely derived from northern European migrants, so that racial variations in the rate of incident cataract could influence the need for cataract surgery in different communities.9,28,32
Access to cataract surgery could also be reduced in areas of social disadvantage or in rural communities. These factors could lead to substantial regional variation in the incidence of cataract surgery.
In summary, this study provides data on the 5 year incidence and ocular predictors of cataract surgery from a representative older Australian community. Our population based findings may be useful in the future planning of cataract surgical services. Incidence data provide a measure of the ongoing requirements for cataract surgery while data on the prevalence of significant cataract associated with visual impairment describe only the backlog of surgical cases. Our current 10 year follow up of this cohort will permit an examination of factors that have a greater impact over the longer term.