Objectives: To determine the incidence of nonarteritic anterior ischemic optic neuropathy (NAION) after cataract extraction and to use the incidence to evaluate the causal relationship between cataract extraction and NAION.
Design: Cohort study.
Participants: Five thousand seven hundred eighty-seven cataract extraction cases at the Bascom Palmer Eye Institute (BPEI) in a 5-year period between January 1, 1993 and December 31, 1997.
Methods: During the study period, an estimated 5787 cataract extraction cases were identified that met the following criteria: (1) the patient was 50 years of age or older, (2) surgery was performed by phacoemulsification or phacofracture techniques and not planned in combination with another procedure, and (3) follow-up was at BPEI. Charts of patients diagnosed with NAION from January 1, 1993 to December 31, 1998 were reviewed to detect the occurrence of NAION within 1 year of surgery. The diagnosis of NAION was based on the following: (1) an acute decrease in vision, (2) associated nerve fiber layer defect on visual field testing, (3) associated relative afferent pupillary defect, and (4) observed optic nerve edema. The exact binomial test was used to compare the incidence of NAION after cataract extraction against the expected incidence.
Main outcome measure: Occurrence of NAION within 1 year after cataract extraction.
Results: Of the 5787 cataract extraction cases, three patients experienced NAION within 1 year of the procedure. Each case occurred after surgery on days 29, 36, and 117, giving an estimated 6-month incidence of 51.8 in 100,000 and a 6-week incidence of 34.6 in 100,000. Both were statistically higher than the previously reported overall incidence of NAION. Two of the three patients had a history of NAION in the contralateral eye.
Conclusions: Cataract extraction is associated with an increased incidence of NAION, which is higher than the reported overall incidence. However, the risk of NAION after cataract extraction is low, with approximately one occurrence in every 2000 cases. A history of NAION in the fellow eye may be a risk factor.