Follow-up of nonarteritic anterior ischemic optic neuropathy with optical coherence tomography

Abstract

Purpose: 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.

Design: Cohort study.

Participants: Twenty-seven patients diagnosed with NAION in our center between April 1, 2004 and March 31, 2006.

Methods: 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.

Main outcome measures: Characteristics of the ONH and their relationship with VA and VFs.

Results: 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.

Conclusions: 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.