Macular spectral domain optical coherence tomography findings in Tanzanian endemic optic neuropathy

Abstract

Bilateral optic neuropathy in Dar es Salaam is now considered endemic and is estimated to affect 0.3-2.4% of young adults. The condition is characterized by a subacute bilateral loss of central vision of unknown aetiology. Findings of spectral domain optical coherence tomography have not previously been reported for these patients. All patients diagnosed with endemic optic neuropathy over a 2-year period at the Muhimbili National Hospital underwent spectral domain optical coherence tomography macular imaging. Scans were graded qualitatively for severity of retinal nerve fibre layer loss as well as the presence of microcystic macular changes, which have not previously been described in this condition. Of the 128 patients included (54.7% male; median age 20 years), severe retinal nerve fibre layer loss was found in 185 eyes (74.0%). There was full concordance in retinal nerve fibre layer thickness between the two eyes in 113 (91.1%) patients. Microcystic macular spaces were found in 16 (12.5%) patients and were bilateral in nine (7.0%) individuals. These changes were typically more prominent in the nasal than the temporal macula, predominantly involving the inner nuclear layer, and often occurred in an annular configuration that was evident on en face infra-red imaging, though not discernible on colour fundus photography or clinically. All patients with microcystic macular changes had severe thinning of the retinal nerve fibre layer (P = 0.02). Four patients in whom cystic spaces were demonstrated had sequential scans, and there was no detectable alteration in the configuration of these changes over a period of up to 16 months. This is the first study to document optical coherence tomography findings in endemic optic neuropathy. We have observed symmetrical severe loss of the caeco-central projection (papillomacular bundle) with otherwise well-preserved macular architecture. Also, we have observed microcystic retinal changes in a significant proportion of patients, which were associated with severe retinal nerve fibre layer loss. Similar changes have recently been reported from optical coherence tomography images of patients with multiple sclerosis, relapsing isolated optic neuritis, dominant optic atrophy, Leber's hereditary optic neuropathy and a patient with a chronic compressive optic neuropathy, supporting the hypothesis that this may be a non-specific phenomenon secondary to ganglion cell death. The correspondence of the changes to an annulus discernible on infra-red en face imaging, but not using other conventional retinal imaging techniques highlights the potential usefulness of this modality.

Keywords: endemic optic neuropathy; epidemic optic neuropathy; microcystic macular changes; microcystic macular oedema; optical coherence tomography.