An investigation into the prevalence and incidence of optic neuropathy following cataract surgery reveals some controversial findings.
The link between cataract extraction as a potential contributor to nonarteritic anterior ischemic optic neuropathy (NAION) was first identified in 1951, and subsequent assessments of the temporal association have strongly supported that relationship.
In this study conducted between 2010 and 2014, the authors included 188 patients with a diagnosis of NAION to assess the relationship between anesthetic and surgical techniques and the incidence and prevalence of so-called post–cataract surgery optic neuropathy (PCSON). Of these patients, 18 (9.6%) underwent cataract surgery during the year prior to developing NAION, while the remainder developed NAION spontaneously.
The investigators found no significant temporal patterns associated with subsequent development of NAION in the operated eye (P=0.28). Additionally, they found no increased risk of PCSON to the fellow eye. Based on this cohort, the researchers estimate the incidence of NAION occurring within 1 year after cataract surgery to be 10.9 in 100,000 cases.
The authors conclude that the prevalence and incidence of NAION after modern cataract surgery are comparable to those of the general population, and concern regarding an increased risk of NAION may be unwarranted.
These findings, however, were disputed in an accompanying editorial by Timothy J. McCulley, MD and his colleagues, highlighting the limitations of retrospective studies and the difficulty in studying the etiology of rare diseases.
First, the editorial notes that the authors fail to emphasize that NAION risk factors were significantly less prevalent in the PCSON group (P=0.008), which includes recognized factors such as current tobacco use and hyperlipidemia. This oversight suggests that the study and control groups were not well matched.
Second, both the editorial and the paper agree that using a single diagnostic code may have led to underestimating of the true incidence of NAION after cataract extraction. Patients with NAION may have been assigned alternate diagnostic codes, such as visual field defect, optic disc edema or optic atrophy, among others. Moreover, the small sample size with a very large confidence interval further illustrates the lack of precision in the study estimate.
Finally, the editorial reasons that this study population was too small to determine a temporal relationship between these 2 events, which would have required "a very profound imbalance to achieve statistical significance." They also go on say that “it is probably premature and arguably reckless to state that there is no longer any need for concern [from cataract surgery]. With the potential devastating consequence of bilateral NAION, proceeding with caution when considering cataract extraction in patients with a history of NAION seems prudent and appropriate.”
While the findings do contribute to the understanding of optic nerve ischemia and intraocular surgery, Dr. McCulley and his colleagues suggest that the responsible approach is to draw measured, tempered conclusions.