McCulley TJ, Lam BL, Feuer W. Incidence of nonarteritic anterior ischemic optic neuropathy associated with cataract extraction. Ophthalmology 2001;108:1275–1278.
Original study reprint requests: Timothy J. McCulley, 500 Lincoln Park Boulevard, Suite 104, Dayton, OH 45429–3487.
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.
Bascom Palmer Eye Institute (BPEI) Miami, FL.
Supported in part by Research to Prevent Blindness, Inc., New York, NY.
During the study period, an estimated 5,787 cataract extraction cases were identified that met the following criteria: (i) the patient was 50 years of age or older, (ii) surgery was performed by phacoemulsification or phacofracture techniques and not planned in combination with another procedure, and (iii) 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: (i) an acute decrease in vision, (ii) associated nerve fiber layer defect on visual field testing, (iii) associated relative afferent pupillary defect, and (iv) observed optic nerve edema. The exact binomial test was used to compare the incidence of NAION after cataract extraction against the expected incidence.
Occurrence of NAION within 1 year after cataract extraction.
Of the 5,787 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.
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 1 occurrence in every 2,000 cases. A history of NAION in the fellow eye may be a risk factor.
The authors set out with a laudable goal, to determine the incidence of post–cataract surgery nonarteritic ischemic optic neuropathy (AION) and evaluate a possible causal relationship between cataract surgery and AION. The study design and setting was ideal to try to answer this question, because it was performed in an institution in which a large number of cataract surgeries were done and adequate follow-up was available to determine the incidence of AION. They identified three patients with AION occurring within 1 year of cataract surgery out of approximately 5,800 surgeries. They concluded that this was a higher rate than expected based on the previously reported natural history of the disease and that therefore cataract surgery was associated with an increased risk of AION. The authors acknowledge some of the obvious limitations of their study, particularly the retrospective nature of the study with an inability to be certain that all cases were captured; the fact that certain risk factors, like diabetes mellitus, for cataracts are also risk factors for AION; that their population was ethnically different than the population used to determine incidence rates of AION in the general population; and finally the possibility that a sampling error occurred because incidence rates were determined based on considering only half of the number of patients who actually had cataract surgery in this period.
Practically speaking, it is impossible to know based on these data whether cataract surgery is an important risk factor for AION. In all three instances, AION occurred months later, making it certainly possible that AION occurred independent of the surgery. Despite these limitations, the study is an excellent effort to try to answer a difficult question. A prospective study could never be done to address this, and therefore this is the best information we have on the subject. It is comforting that none of the patients had AION within 48 hours of surgery. This type of post–cataract surgery AION is much more disconcerting and, based on this series, must be exceedingly rare. Cataract surgeons can advise their patients that there is a very slight increased risk of AION in association with cataract surgery. Two of the three patients with AION in this study and had prior AION in the contralateral eye. Because prior AION in the contralateral eye is a well known risk factor for AION, these patients may need to be counseled most carefully.