The eye maintains its spherical shape because it is ‘inflated’ to above atmospheric pressure. The normal range of intraocular pressure is between 12 and 20 mm Hg, the average being 14 mm Hg. Aqueous humour (often abbreviated to aqueous) is formed by the ciliary epithelium. Its formation can be divided into two components, ultra-filtration and secretion. Ultrafiltration describes the process whereby aqueous humour is ‘filtered’ out of the blood stream as a result of the blood pressure in the ciliary capillaries being higher than the intraocular pressure. Secretion is an active metabolic process and is not dependent on pressure; it is diminished by drugs (e.g. acetazolamide) which inhibit the formation of aqueous, and ischaemia.
KeywordsRetina Sponge Mannitol Excavation Cataract
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