Unoperated cataract remains the most common cause of blindness worldwide, even though the disorder can be effectively and inexpensively treated with a standard surgical procedure. Visual impairment attributable to unoperated cataract has been reported to have a variety of harmful effects on patients. Most importantly, previous population-based cohort studies have shown increased mortality in older persons with unoperated cataract.
Since surgery can restore visual function and improve quality of life among cataract patients, it is perhaps not surprising that operative intervention may also decrease mortality risk. Investigators from the Blue Mountains Eye Study (BMES) previously compared participants with visual impairment corrected by cataract surgery at baseline with participants with cataract and visual impairment who had not had surgery. They found significantly better long-term (15 years) survival among the former group, even after accounting for known cataract and mortality risk factors and indicators of general health. However, the conclusion of this study was less than certain, in view of the fact that some cataract patients were prevented from undergoing surgery because of poor general health. This made it difficult to distinguish the directionality of causation; that is, whether cataract surgery led to better health and survival, or whether better health led to greater likelihood of undergoing cataract surgery.
To better ascertain whether the decrease in mortality among persons undergoing cataract surgery is in fact attributable to the effects of surgery in alleviating visual impairment, Wang and associates have now carried out a prospective study in a large cohort of older persons, the Australian Prospective Cataract Surgery and Age-related Macular Degeneration study. Between 2004 and 2007, 1864 patients undergoing phacoemulsification at a tertiary hospital were recruited. Demographic and anthropomorphic data of all eligible participants were collected at baseline, and death information was obtained from the Australian National Death Index (NDI) through October 2011. Presenting visual impairment was defined using either the surgical eye or the better-seeing eye, and categorized as none (presenting visual acuity ≥20/40), mild (presenting visual acuity <20/40-20/60), and moderate-severe (presenting visual acuity <20/60).
Among 901 patients with complete data whose preoperative presenting visual acuity was <20/60, 60.4%, 15.5%, and 24.1% had no visual impairment, mild visual impairment, and moderate-severe visual impairment in the operative eye, respectively, at 1 month postoperatively. Though the age-standardized mortality did not differ significantly between the no visual impairment (24.1%) and mild visual impairment (24.1%) groups, mortality among the moderate-severe visual impairment group (30.6%) was significantly higher ( P = .044) than in the no visual impairment group, after adjusting for indicators of general health and frailty. Supplementary analyses using the better-seeing eye showed similar results, though the adjusted difference between the no visual impairment and moderate-severe visual impairment groups did not reach statistical significance.
These findings are very important from an advocacy standpoint, as governments consider how to allocate scarce healthcare dollars. These data suggest that an investment in cataract surgery not only yields improvements in vision and quality of life, but may in fact reduce the burden of mortality among older persons, potentially making such investment more attractive to governments.
As the authors themselves point out, the impact on their results of other potential confounding factors (such as social support and self-reported health status, which are known to be associated with mortality but were not measured in the study) is unknown. Further, patients with moderate-severe visual impairment (presenting visual acuity <20/60) were grouped into a single category, presumably for reasons of power. If these patients were further divided into moderate (presenting visual acuity <20/60-20/200) and severe (presenting visual acuity <20/200) visual impairment, the reader would have a clearer sense of the impact of varying degrees of visual impairment on survival and mortality.
Nonetheless, as eye care providers are challenged to place vision-saving interventions more reliably within the context of the entire healthcare system, data such as these are valuable in establishing the true importance of healthy eyesight in sustaining wellness.