The Croonian lecture : in which the power that enables the eye to see distinctly at different distances is considered / by Everard Home.

  • Home, Everard, Sir, 1756-1832.
Date:
[1795]
Catalogue details

Licence: Public Domain Mark

Credit: The Croonian lecture : in which the power that enables the eye to see distinctly at different distances is considered / by Everard Home. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    are continued on to the edge of the cornea, and terminate, or are inserted, in its external lamina; their action will therefore extend to the edge of the cornea, 4th, That in changing the focus of the eye from seeing with parallel rays to a near distance, there is a visible alteration produced in the figure of the cornea, rendering it more con- vex ; and when the eye is again adapted to parallel rays, the alteration by which the cornea is brought back to its former state is equally visible. Having supported these facts by the evidence of anatomical structure, and absolute demonstration, I shall consider them to be established; and make some observations upon the muscular and elastic power by which so very curious an effect as the ad- justment of the eye is produced. The four straight muscles of the eye are attached to the bot- tom of the bony orbit near the foramen opticum ; they become broader as they pass forward, and when arrived at the anterior part of the eye-ball, are insensibly changed for tendons ; these adhere to the sclerotic coat, and terminate in the external lamina of the cornea, which appears to be a continuation of them. When we consider the situation of these muscles, it is evi- dent that their action will produce three very different effects upon the eye, according to circumstances. When they act se- parately, they will move the eye in different directions ; when together, witli only a small quantity of contraction, they will steady the eye-ball; and when this is increased they will com- press the lateral and posterior parts of the eye. This compres- sion of the eye will force the aqueous humour forwards against the centre of the cornea, while the circumference is steadied D2