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Ophthalmic artery perfusion pressures and retinal arteriolar calibres were studied in 10 human subjects when sitting, standing, and lying. Differing responses in perfusion pressure were found; autoregulatory responses were found in 13 of the 18 significant calibre changes on moving from sitting to standing and 13 of 22 significant calibre changes on moving from standing to lying. The remaining significant calibre changes were non-autoregulatory, the arterioles dilating with perfusion pressure increase and constricting with decrease.

Within the discipline of ophthalmology, fluorescence angiography has achieved popularity in the past decade as a method of investigation, demonstrating abnormalities in the retinal and choroidal circulations. Alterations in Bruch's membrane and the overlying pigment epithelium are seen as modifications in the pattern of underlying choroidal fluorescence. A large volume of literature has accumulated around the technique and its interpretation in various aspects of ocular disease. In this issue of the J7urnal of Medical Genetics dedicated to Professor Arnold Sorsby, it is appropriate to present a brief essay on the application of this technique to a subject of interest to him, genetically determined degenerations of the fundus oculi.

The gas delivered from a cylinder of Entonox (50% nitrous oxide and 50% oxygen) may not contain adequate quantities of oxygen if the cylinder has been cooled and then allowed to warm up in a vertical position.The composition of gas delivered from cylinders cooled to not lower than -40 degrees C. remains unaltered if the cylinders are rewarmed for 24 hours in a horizontal position at a temperature of not less than 5 degrees C.Cylinders of Entonox delivered in cold weather should be stored in a horizontal position at 5 degrees C. or more for at least 24 hours before use.