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George A. Cioffi, MD; Lin Wang, PhD; Brad Fortune, PhD; Grant Cull, B Ag Sci; Jin Dong, PhD; Bang Bui, PhD; E. Michael Van Buskirk, MD

Arch Ophthalmol. 2004;122:1517-1525.

Objectives  To evaluate the effects of chronic optic nerve ischemia in a nonhuman primate model and to evaluate the regional variability of axonal loss.

Methods  Unilateral ischemic optic neuropathy was induced by administration of endothelin-1 to the retrobulbar space via osmotic pumps in 12 primates for 6 to 12 months. The transversely cut sections were stained and divided into 16 regions. Average axonal density in each region was quantified and compared with the untreated contralateral control eyes.

Results  Mean axonal density was 208 310/mm² and 220 661/mm² in treated and control eyes, respectively (P = .03, 1-tailed paired t test), for the entire group. Two-way analysis of variance showed a significant effect of endothelin-1 on overall axonal density for the experimental group (P<.001). Among the nerves with significant axonal loss, the mean axonal loss was 11.6% (4%-21%). Regional mapping of the damage showed the axonal loss varied in the damaged nerves; the damaged regions often clustered within specific quadrants.

Conclusion  Chronic ischemia induced by local administration of endothelin-1 causes significant loss of optic nerve axons with varying regional susceptibility.

Clinical Relevance  Localized damage occurs in other types of optic neuropathy, such as glaucoma, and may result from regional differences in anatomy, metabolism, or vasculature of the primate optic nerve.

From the Discoveries in Sight, Devers Eye Institute, Portland, Ore. The authors have no relevant financial interest in this article.

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