A handbook of local therapeutics / edited by Harrison Allen.

Date:
1893
Catalogue details

Licence: Public Domain Mark

Credit: A handbook of local therapeutics / edited by Harrison Allen. Source: Wellcome Collection.

    215/554 (page 203)
    Illation of the sympathetic nerve, though some authorities think that it has also some paralyzing effect on the iritic filaments of the oculo-motor. Mydriasis from section of the third nerve, as also that from atropine, is increased by it. It has no effect on the pupil when the sympathetic is divided, and fails to act in birds, whose iris muscles are striated. Its effect on the accommodation is comparatively slight. Widening of the palpe- bral fissure, similar to that found in exophthalmic goitre, and the sup- pression of winking are supposed to be due to contraction of Muller's involuntary orbital muscular fibres, though some influence may be attrib- uted to absence of reflex from the anaesthetised cornea and conjunctiva. Cocaine increases the absorbing power of the cornea, probably by dimin- ishing the amount of fluid in its lymph spaces. Anaemia of the con- junctiva and diminished secretion of tears are results of contraction of blood-vessels, and decreased intraocular tension may be due to the same cause. The latter efl'ect in healthy eyes is generally admitted, but seve- ral cases have been reported in which glaucoma was said to be induced by its use. It is possible that the mechanical effect of a widely dilated pupil (see article on atropine) might hasten the onset of an attack of glaucoma, but the cases reported are much too few, compared to the enormous number of applications of cocaine made daily all over the civilized world, to exclude the probability of coincidence. The danger of constitutional effects resulting from the application of cocaine to the eye is so slight that it may practically be disregarded. A few cases have been recorded in which some inconvenience was occasioned, but in none were the symptoms alarming (Frost, Am. Jour. Med. Set., April, 1887). A real danger, however, is sometimes met with in its effects upon the cornea, whose nutrition seems to be profoundly influenced by strong solutions. Some surgeons have thought that a loss of firmness and elas- ticity of the cornea, a flaccid condition, produced by its use, might interfere with the accurate coaptation of incisions, but no serious diffi- culty seems to have been experienced from this cause. Its occasionaj injurious effect upon the corneal epithelium is well established. Disturb- ance of this causes loss of polish and haziness of the cornea, with super- ficial depressions due to thinning of the epithelial layer and consequent slight derangement of refraction, or there may be vesication or desquama- tion. The whole corneal epithelium has been raised in a bleb. Even in these cases there is not usually any permanent injury if the cocaine is promptly discontinued. The loss of moisture is at least an important factor in producing this condition, and in experiments on animals des- quamation has been prevented by keeping the eyes closed. Cases have been reported in which the anaesthesia lasted for several days. {Annal. Oculistf 1885.) Deeper corneal lesions are more rare, but in quite a number of cases the use of cocaine has been followed by interstitial