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Letter to the Editor Comments on ‘Hemispheric Retinal Branch Vein Occlusions’ by F. J. Gómez-Ulla de Irazazabal et al., published in Ophthalmologica, Basel 198:14–22 (1986) I was interested to read the paper by F.J. Gomez-Ulla de Irazazabal et al. The authors made some erroneous and misleading statements on the subject which require to be rectified. The two retinal venous trunks, draining the upper and lower halves of the retina, usually join on the optic disc to form the central retinal vein. However, in about 20% of the population, as a congenital anomaly, the two trunks enter the optic disc separately and join each other within the optic nerve at a variable distance from the optic disc [2–4]. The main retinal vein draining the upper or lower half of the retina may be (i) occluded at the arterio-venous crossing on the retina near the optic disc or on the surface of the optic disc (as was seen in 2 of the 9 cases of the authors), or (ii) if the eye has the anomalous pattern mentioned above, the site of occlusion in the involved trunk may be within the optic nerve, similar to that occurring in central retinal vein occlusion (seen in the remaining 7 cases of the authors). In our prospective studies on retinal vein occlusion, we discovered that occlusion of one of the two venous trunks (draining one or the other half of the retina) within the optic nerve represented pathogenetically and clinically an entirely new entity which was erroneously diagnosed till then as a variant of ordinary major branch retinal vein occlusion [5]. We called this new entity ‘Hemi-central Retinal Vein Occlusion’ [5]. Our studies clearly showed that the hemi-central retinal vein occlusion clinically and pathogenetically is closely related to central retinal vein occlusion and unrelated to major branch retinal vein occlusion, because, unlike major branch retinal vein occlusion, it showed the following features: Site of occlusion: in the optic nerve. Location of venous collaterals: on the optic disc. Raised intraocular pressure: seen in 1/3 of the patients. Ischemic and non-ischemic types: The retinopathy in this condition, as in central retinal vein occlusion, is either of ischemic (in about 1/3) or non-ischemic (in about 2/3) type [5, 6]. In contrast to that, in major branch retinal vein occlusion, because of its totally different pathogenetic and hemody-namic mechanisms, the retinopathy in the vast majority is of the ischemic type. de Irazazabal et al. [1] made the following conclusion, based on a retrospective review of case records of only 9 cases: Letter to the Editor · Lettre à la redaction · Brief an die Redaktion 155