Op-brai130155 1..4

Sir, it has been reported that microcysts from macular oedema occur in 4.7% of patients with multiple sclerosis (Gelfand et al., 2012). It is now evident that these microcysts do not represent oedema, nor is their occurrence a specific feature of demyelinating disease, because they have been identified in patients with Leber's hereditary optic neuropathy, Kjer's dominant optic atrophy, and optic glioma (Abegg et al., 2012; Barboni et al., 2013). However, their precise aetiology has remained a mystery. As pointed out by Abegg et al. (2012), the classical ocular pathology literature provides a clue to the formation of microcysts. Van Buren (1963) described retrograde trans-synaptic degener-ation of the inner nuclear layer in histological sections of the retina after lesions of the optic nerve or chiasm, causing 'cystic degeneration' that resembles the 'microcysts' now being imaged with optical coherence tomography. Gills and Wadsworth (1967) found a 15–60% reduction in cell population in the inner nuclear layer in nine patients with longstanding blindness from compres-sive or traumatic lesions of the optic nerve. In at least three cases, microcycsts were present in the inner nuclear layer (Fig. 1). In two patients with more recent blindness, cell loss was not observed. Presumably, sufficient time had not elapsed for trans-synaptic degeneration to occur. Gills and Wadsworth (1967) also reported cell loss in the inner nuclear layer in patients with optic atrophy from multiple sclerosis. Figure 1 (A) Histological section of the retina showing cysts in the inner nuclear layer following retrograde trans-synaptic degeneration from a tumour of the optic nerve. Reproduced from Gills and Wadsworth (1967) with permission from James P. Gills. (B) Image obtained by optical coherence tomography from a patient with optic atrophy, showing cysts in the inner nuclear layer. IPL = inner plexiform layer; INL = inner nuclear layer; OPL = outer plexiform layer; HFL = Henle fibre layer; ONL = outer nuclear layer.