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.

The prevalence of microcystic macular changes on optical coherence tomography of the macular region in optic nerve atrophy of non-neuritis origin: a prospective study

“…The literature on other conditions is only emerging, but it might be prudent to consider neuroimaging if metabolic and hereditary conditions have been excluded and there is no other obvious ophthalmological explanation 11 14 15…”

“…It has also become apparent that microcystic macular changes occurred in ophthalmological degenerative diseases like age-related macular degeneration, diabetic retinopathy, vascular occlusion and with epiretinal membranes 14 15. As the aetiology of this retinal abnormality remains unknown and the evidence for oedema not conclusively been provided, Kisimbi et al 11 suggested to be careful about the terminology. Therefore, Abegg et al 13 proposed to refer to a ‘retrograde maculopathy’.…”

“…Kisimbi et al 11 were also first to report that infrared imaging may be a convenient method to demonstrate the localisation of microcystic changes in the retina. This has since been confirmed and scanning laser ophthalmoscopy (SLO) was added to the list more recently 8 10 12 13.…”

The Clinical Spectrum of Microcystic Macular Edema

“…6,7 It was suggested that MME originated from breakdown of the bloodretinal barrier or focal inflammation. 1 However, microcystic changes in the INL were also described in compressive optic neuropathy (due to glioma), 8 Leber's hereditary optic neuropathy, dominant optic atrophy, 9 and endemic optic neuropathy, 10 suggesting retrograde trans-synaptic degeneration from optic neuropathy as a causative factor for degeneration of the INL with formation of cystic spaces. 8 Microcystic macular edema is not restricted to neurologic etiologies and has been described in ARMD, group 2A idiopathic juxtafoveolar retinal telangiectasis, and tamoxifen retinopathy.…”

Microcystic macular oedema in optic neuropathy: case series and literature review

“…2 They are characterized as a band of perifoveal thin, elongated 'cysts' of hyporeflectivity in the inner nuclear layer on optical coherence tomography. Since then, MME has been found not to be specific for demyelinating conditions 3 and it has been described in a number of conditions associated with optic atrophy ranging from slowly progressive disease such as glaucoma, 4 genetically determined disease such as autosomal dominant optic atrophy 5 and Leber´s hereditary optic neuropathy, 6 inflammatory disease such as neuromyelitis optica, 7,8 in Tanzanian endemic optic neuropathy 9 and optic atrophy caused by compression. 10 In some patients, the oedema is dynamic and may fluctuate over time.…”