OCR Text |
Show $2 or THE Lxrmcrron or 'rnn cA'rnnaer. : Ax 9435M mum city in the cornea, is more essentially necessary, previous to performing the operation of extraction, than of couching. Extraction, let me say, is a bad term, as it indicates that. the intention of the operation is to make an incision, and to pull out the opaque body. This idea is as dangerous, as it is incorrect. The principle on which the operation is- done, is simply this. The coats of the eye are tense over the contained humours. Over the coats of the eye, are expanded the tendons of the muscles, while the eyelids have in them the fibres of the orbieularis muscle. The moment that the eye is wounded therefore, the humour escapes at that part. If an accidental wound be made on the white of the eye, the vi- treous humour escapes in part. If the cornea be wounded, the aqueous humour escapes. But although the cornea be punctured, and the water escape, it does not fall flaccid. But the iris and the lens are pushed forward by the tension of the coats on the vitreous humour, and they take the place of the aqueous humour. Should the cornea not be punctured merely, but cut with so wide a wound, as to allow the lens to pass, the pressure on the Vitreous humour by the coats and muscles of the eye will be so great, that the lenswill be thrown in through the pupil, and escape by the wound. The operation to be performed, then, is not to extract tlm cataract, as we speak of extracting the stone from the blad~ der; but only to make such an opening in the cornea, as to allow the cataract to be forced out by the tension of the coats of the eye, which is continual ; or by the action of the musales of the eye. The necessity of attending to this principle during the operation, I hope will be presently evident. [may r‘jj- -w"4,<.,:-¢,- f..-;,a.\ , ‘ a , INSTRUMENTS . Ir the operation is successfully done, no other instrument need be used, but a knife, of a form somewhat peculiar, and adapted to make the proper incision of the cornea. The lmife x) is of the form seen in the succeeding marginal plate p. 45. The point must be very sharp, the back straight, not sharp, and yet not thick; the curved edge very sharp, and the mid dle of the knife the thickest, and strongest part of it ; in the first place, that the knife may have strength to be pushed through the cornea, and in the next place, that it may effect‘ ually fill up the wound as it is pushed forward. The broad est part of the knife must be fully two thirds of the diameter of the cornea. The incision is made, by passing the point of the knife through the cornea, and across the fore-part. of the eye, with one uniform motion, and the point entering on one side the cornea, near its attachment to the selero-tica, transfixes the op positc point, and being still carried forward, the lower edge of the knife cuts freely through the whole lower segment of the cornea, until it is disengaged. But if the breadth of the knife be not sufficient to make its way out, when thus uni: formly pushed onward, the edge requires to be pressed down ; an incision larger than the knife can fill up is consequently made, the aqueous humour escapes, and the iris is pushed iorward on the edge of the knife! A little oil should be on the point of the knife. To suspend the eyelid, and in some degree to fix the eye; the wire speculum is best in the hands of the assistant; the pressure to fix the eye must be made by the tips of the surgeon's fingers, at the same time that he holds down the lower eyelid. A gold needle is among the apparatus of the oculist. The use of this is, to break or out the capsule, when after cutting the cornea, that membrane strongly resists the effort of the muscles, to protrude the lens. The point should rather be rough than sharp, whether it be made of gold or of any other metal, is of little consequence. Forceps too are necessary, and they must be of such a form and niceness, that we may introduce them under the flapof the cornea, and seize any shred of opaque membrane, that may present in the pupil. -44: Liv ;.~_ .fi'...-": W5»3*- «- -u/.. =:.:." by»... OF THE EXTRAC'IiON OF THE CATARACT. |