By Hugh Davison (Auth.)
For 40 years Hugh Davson's body structure of the attention has been considered as the major textbook in ophthalmology. This largely revised and up to date 5th variation keeps this acceptance and offers the author's lifelong services to the coed. The constitution and content material were revised to maintain abreast of present instructing and learn pursuits, whereas conserving the fashion and readability of prior variations
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Additional info for The Physiology of the Eye
Atropine, the cholinergic blocking agent, may raise the pressure in glaucoma. In the normal human eye the * It is impossible to give a fair and balanced account, in a short space, of the studies on adrenergic mechanisms in aqueous humour dynamics; the situation is complicated by the possibility that there are antagonistic a- and /factions, as typified by the actions of noradrenaline and isoproterenol respectively, the one possibly acting mainly on secretionrate and the other on resistance. A further complication is the use of different species, usually the rabbit and monkey; and finally the effects are often so small as to be beyond the resolution of the methods of measurement.
50 O I 40 -C C E T 30 Left eye 3 Q. ) 50 60 70 FIG. 26. Intraocular pressure of the rabbit. At points marked C the left common carotid artery was clamped, and at points marked R it was released. (Davson & Matchett, J. ) By injecting saline continuously into the anterior chamber we may experimentally increase the flow of fluid through the eye and test the applicability of the simple equation relating flow-rate to pressure-drop; Langham found that the equation did not hold, the rise in pressure for a given increase in flow being smaller than predicted, and his results suggested some homeostatic mechanism that decreased the resistance to flow as the intraocular pressure rose.
Unfortunately the significance of ascorbate in the eye is not yet understood, so that the reason why the cat, dog and rat can manage with such low concentrations, whilst the rabbit and other species require high concentrations, is not evident. The suggestion that the lens actually synthesizes ascorbate and pours it into the aqueous humour has been disproved, at any rate as a significant source of the vitamin. THE BLOOD-AQUEOUS BARRIER Our knowledge of the relationships between aqueous humour and plasma has been furthered by a study of the exchange of materials between the two fluids, studies of what has come to be known as the blood-aqueous barrier.