Follow-up of Nonarteritic Anterior Ischemic Optic Neuropathy with Optical Coherence Tomography

Abstract

To study the characteristics of nonarteritic anterior ischemic optic neuropathy (NAION) as measured with optical coherence tomography (OCT) at diagnosis and during the first year after the episode. Cohort study. Twenty-seven patients diagnosed with NAION in our center between April 1, 2004 and March 31, 2006. Patients diagnosed with NAION underwent at the time of diagnosis and 6 weeks and 3, 6, and 12 months after presentation a complete ophthalmologic evaluation, including determination of Snellen visual acuity (VA), visual fields (VFs) (standard automated perimetry, Swedish Interactive Threshold Algorithm strategy 24-2), and optic nerve head (ONH) scanning with StratusOCT. Characteristics of the ONH and their relationship with VA and VFs. Initial mean retinal nerve fiber layer (RNFL) thickness in the affected eye was 200.9 microm (standard deviation [SD], 52.3 microm); this represented a 96.4% increase relative to the fellow eye. Percentages of RNFL loss 3, 6, and 12 months after onset were 38.9%, 42.3%, and 43.9%, respectively. At the 6-month visit, RNFL percentage decreases for the superior, nasal, inferior, and temporal quadrants were 51.5%, 28.5%, 41.2%, and 38.2%, respectively. Reduction in the superior quadrant RNFL thickness was statistically higher. Using regression analysis, it was found that for every micrometer of mean RNFL thickness lost there was a 2-decibel decrease in VF mean deviation (MD) and that there was a 1-line drop in Snellen VA for every 1.6 microm lost. The mean ONH area was 2.6 mm2 (SD, 0.4) in the unaffected eye; there was no correlation with VA, VF MD, or RNFL thickness of the affected eye at the last follow-up visit. Optical coherence tomography can diagnose optic disc edema and monitor RNFL loss over time. It is most useful at onset and 6 months after NAION, when RNFL loss has reached a plateau and is correlated with visual function. Future studies that aim to determine if a drug or intervention is useful for treating NAION may include OCT assessment of the RNFL thickness, because it provides an objective outcome measure correlated with visual performance.