Eyeworld

EW FEATURE 30 Neuro-ophthalmology for the anterior segment surgeon • June 2018 by Vanessa Caceres EyeWorld Contributing Writer AT A GLANCE • A study published late last year reported a lower risk of NAION after cataract surgery using modern surgical techniques. • In the study, only 9.6% of patients who had cataract surgery in the previous year developed NAION. • Some have criticized the study's retrospective nature, small size, and study design. • Some neuro-ophthalmologists think the risk for postop NAION is much lower now; others think there is still a higher risk and advise waiting on fellow eye surgery until there is significant visual compromise if NAION has occurred in the first eye. The findings led the authors to conclude that the prevalence and incidence of NAION after cataract surgery are comparable to those of the general population and that there is no significant temporal re- lationship between modern cataract surgery and the subsequent devel- opment of NAION in the operated eye. "We suspect that this differ- ence reflects the shift in cataract surgery methods over the last few decades, from intracapsular and extracapsular methods with retrob- ulbar or peribulbar anesthesia to a predominantly phacoemulsification technique, carried out under topical anesthesia," the authors wrote. The study acknowledged that use of a single ICD-9 diagnostic code for NAION could be a poten- tial source of error. "[S]ome patients with NAION may have been as- signed, at least initially, an incorrect or inadequate diagnostic code, such as visual field defect, optic disc edema, or optic disc swelling," they wrote. Although this could invali- date the results if it occurred even one or two times, all of the patients were examined by neuro-ophthal- mologists who would have made the appropriate diagnosis, said study author Neil Miller, MD, Frank B. Walsh Professor of Neuro-oph- thalmology, Wilmer Eye Institute, Johns Hopkins School of Medicine, Baltimore. There was a total incidence of 10.9 cases per 100,000 (95% CI, 1.3, 39.4). No significant temporal pattern was associated with NAION case distribution. Among the 18 patients who had cataract surgery within the previous year, 17 had bilateral sequential cataract surgery. Of these, four (23.5%) had devel- oped bilateral PCSON, whereas in 13 (76.5%), the PCSON was unilateral. "Of the 13 patients with unilateral PCSON after bilateral sequential cataract surgery, five had developed it in the first operated eye but not in the second, and eight had devel- oped it in the second operated eye but not the first," the authors wrote. All patients in the group were older than age 58 (median age, 71 years), and 14 had at least one known sys- temic disease that has been consid- ered a NAION risk factor. Local anesthesia was used in all but one procedure; topical anesthesia was most commonly used, followed by retrobulbar and sub-Tenon's anesthesia. No patients had immediate postop NAION; in fact, the median interval between cataract surgery and NAION was 173 days, with a range of 9–328 days, according to the authors. The analysis found that sponta- neous NAION was more common in current smokers and in those with hyperlipidemia compared with the PCSON group. ic perioperative hypotension, or a combination of these factors. Although exact causes of the delayed form of NAION are unclear, there may be a connection with intraocular surgery-related posteri- or pole edema as this involves the nerve and results in vascular com- pression, according to the study's authors. Because of changes in anes- thetic and surgical techniques, the authors decided to investigate the incidence and prevalence of post-cataract surgery optic neurop- athy. Study researchers included pa- tients with a diagnosis of NAION as identified with the ICD-9 diagnostic code 377.41 (ischemic optic neu- ropathy), which led to 651 patients. These patients were seen within the Wilmer Eye Network system between 2010 and 2014. Inclusion criteria included a history of acute unilateral vision decrease, a visual field defect consistent with NAION, a relative afferent pupillary defect, and observed optic disc swelling. The main study outcome mea- sure was the prevalence and inci- dence of PCSON and the temporal association between surgery and PCSON onset. A secondary outcome was the risk of PCSON in the fellow eye in patients who had a prior uni- lateral spontaneous NAION. Among the 651 patients, 165 of those (25.3%) were excluded be- cause their NAION took place before the study period, and another 114 (17.5%) had experienced NAION but did not meet the other study inclusion criteria. Yet another 184 patients were excluded because their visual loss was subsequently linked to a process other than NAION, such as retinopathies or optic neu- ritis. Ultimately, 188 patients with NAION were included in the study, with a median age of 63.8 years. Fifty-three percent of the patients were male, and 88.8% of all patients were white. Among the study group, 18 patients (9.6%) had a history of ipsilateral cataract surgery within a year prior to developing NAION (the PCSON group). Study finds a lower risk nowadays, but not all ophthalmologists agree H ow high is the risk for nonarteritic anterior ischemic optic neuropathy (NAION) after uncompli- cated cataract surgery? Results from a study published in 2017 questioned long-held beliefs on this topic. 1 However, not all oph- thalmologists are ready to change their mind on the risk level. The retrospective cohort study, published in the American Jour- nal of Ophthalmology, focused on the prevalence and incidence of post-cataract surgery optic neuropa- thy (PCSON) with the use of today's modern cataract techniques. Cases of NAION have been documented after uncomplicated cataract surgery, and these can appear immediately postoperatively or days, weeks, or months after surgery, the authors wrote. They also cited previously re- ported data that found when PCSON occurs after cataract surgery in one eye, there is a 53% risk of a similar event occurring in the fellow eye if it also has cataract surgery. Some ophthalmologists think there is a link between optic neu- ropathy and increased IOP, raised intraorbital pressure from a retrobul- bar or peribulbar anesthetic, system- Does cataract surgery increase the risk of NAION in some patients? Some neuro-ophthalmologists think the risk for postop NAION is much lower now; others think there is still a higher risk and advise waiting on fellow eye surgery until there is significant visual compromise if NAION has occurred in the first eye.

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