Ophthalmic surgery / by Robert Brudenell Carter and William Adams Frost.

  • Carter, Robert Brudenell, 1828-1918.
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: Ophthalmic surgery / by Robert Brudenell Carter and William Adams Frost. Source: Wellcome Collection.

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    fibres or sclerotic foramen, is about a millimetre and a iiali in diameter, and is situated just below the horizontal meridian, with its centre about four millimetres to the nasal side of the posterior pole 1 he aperture is partially closed, at the level of the external surface, by a fine web of white fibrous tissue the lamina cnbrosa, which suffers the nerve fibres and vessels to pass through the sieve-like opening in its structure. Anteriorly the sclera is somewhat con- tracted, so as to form a circular depression (sulcus soleras) around the cornea; and, just in front of this it is traversed near its internal surface by a circular channel, Schlemm's canal (Sc, Pig. ]), w]lich contains and protects an intricate plexus of veins. The sclera is covered in front by the conjunctiva of the lobe ■ and as seen through this membrane, constitutes the ' white of the eye. In infancy it presents a bluish aspect, having then a degree of translucencv which permits the dark colour of the choroid to show through • and m advancing life its whiteness is often obscured by a yellow tinge derived from fatty deposit in the subconjunctival tissue, or possibly in the sclera itself. The cornea (c, Frontispiece), the anterior portion of the external tunic, is a dense membrane of seeming absolute transparency, which forms a portion of 'a smaller spheroid (or ellipsoid) than the sclera, into which it is inserted after the manner of a watch-elass into its setting, the scleral tissue advancing farther anteriorly than posteriorly, and also advancing farther above and below than laterally ; so that the cornea, which is circular as seen from within, appears elliptical in its outer aspect, and has a vertical diameter which is some half a millimetre less than the horizontal. Its general thickness is about a millimetre; aud its surfaces are parallel in its central region, but they cease to be so near the periphery, where its thickness is about two-tenths of a millimetre greater than in the