Comparison of Arteritis and Nonarteritic Anterior Ischemic Optic Neuropathies with the Heidelberg Retina Tomograph

Abstract

Quantitative data are not available regarding the morphological appearance of optic nerve morphology after arteritic anterior ischemic optic neuropathy (AAION) and nonarteritic anterior ischemic optic neuropathy (NAION). The purpose of this study is to evaluate the appearance of the optic nerve head in patients after AAION and NAION with the Heidelberg Retina Tomograph (HRT). Prospective comparative observational study. Thirty-eight patients with either unilateral AAION (15) or NAION (23). Heidelberg Retina Tomograph images were taken of both affected and unaffected eyes. The quantitative changes in the optic nerve head were morphologically evaluated and compared with those of the normal contralateral eyes. Heidelberg Retina Tomograph parameters were analyzed using the uninvolved contralateral eye as a control. The ratio between cup area and disc area was 42% larger in the affected eyes in the NAION group than in the fellow eyes (P = 0.03, t test). In the AAION patients, the ratio between cup area and disc area was 116% larger in involved eyes than in their fellow eyes (P = 0.0003, t test). In addition, in the AAION group, relative to their fellow eyes, the rim area was 27% smaller (P = 0.0006), cup volume was 160% larger (P = 0.021, t test), mean cup depth was 29% larger, cup shape measure differed by 41% (suggesting more excavation), and mean retinal nerve fiber layer thickness was 30% less. Relative to the fellow eyes in the NAION group, the rim area was 6% smaller (P = 0.13, Student's t test), and the cup shape measure was 13% different, although these were not statistically significant. When the uninvolved eyes of the NAION and AAION groups were compared directly, there was no statistical difference between any of the HRT parameters, except mean cup depth (0.09 vs. 0.14 mm, respectively; P = 0.02). This study is the first to demonstrate quantitatively an enlargement and excavation of the optic cup after an event of AAION, but not NAION. The eyes affected with AAION showed significant excavation and enlargement of the optic cup when compared with contralateral uninvolved eyes. All HRT-generated parameters showed changes consistent with increased enlargement and excavation of AAION-involved eyes. These changes were not observed in eyes that experienced an event of NAION.