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Microcystic macular oedema confirmed, but not specific for multiple sclerosis.

Sir, a potentially new sign in multiple sclerosis was described in Brain (Gelfland et al. , 2012). This new sign, microcystic macular oedema, is intriguing because it is considered to indicate breakdown of the blood-retinal barrier with or without microglial inflammation (Gelfland et al. , 2012). There are earlier reports on vascular instability and leakage during inflammation in multiple sclerosis readily seen as sheathing of the retinal veins (Rucker, 1944). Not commented on in the article, but clearly visible from the images (Figs 1A, 3A, B and C in Gelfland et al. , 2012), microcystic macular oedema occurs in areas without vascular sheathing. In fact, in most cases microcystic oedema is seen remote to the inner retinal vasculature (Figs 1A and 3A–C in Gelfland et al. , 2012). Why does microcystic oedema predominantly affect retinal layers close to the very tight inner blood retinal barrier? Are there alternative pathological features to be considered?

One possibility could be Muller cell pathology. Like astrocytes in the brain, Muller cells are responsible for maintaining tissue homeostasis. Muller cells transverse all retinal layers orthogonal …