The calabar bean as a new agent in ophthalmic medicine / by D. A. Robertson, M.D.

  • Robertson, Douglas Argyll, 1837-1909.
Date:
1863
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Licence: Public Domain Mark

Credit: The calabar bean as a new agent in ophthalmic medicine / by D. A. Robertson, M.D. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    left. With the right eye I was able to read small print without the slightest inconvenience, while with the left I was unable to read any but large-sized print, and that only when held at a considerable distance from the eye. At 6.55, the effects of the Calabar bean were passing off the nearest point of clear vision in the right eye, being about 18 inches ft-om the eye. Another drop of the strongest extract of the Calabar bean applied to right eye. At 7.5, distinct vision with the right eye ranged from 6 to 9 inches from the eye; at 7.15 it ranged between 5^ inches and 8 inches; at 7.55 between 5 inches and 15 inches; and at 8.15, objects at all distances beyond 5 inches could be most clearly defined. Very little alteration was observed in the size of the pupils or the vision of the left eye. No fui-ther application of the Calabar bean was made to the right eye, as the effects of the last application lasted imtil the effects of the atropine had almost passed off, and exhibited a marked contrast to the left eye, in which the atropine acted uncontrolled. I have narrated these experiments somewhat in detail, so as to elucidate, as far as possible, the method of action of this new agent and its energy. These experiments prove that the local application of the Calabar bean to the eye induces,—first, A condition of short- sightedness. That this is present, and the cause of the indistinct- ness of distant vision cannot be doubted, as it is relieved by the use of concave glasses. The fact that objects appear larger and nearer than natural may be attributed to the induced myopia. And, second. It occasions contraction of the pupil, and sympathetically dilatation of the pupil of the other eye. We further observe that atropine possesses the power of counteracting its effects, and, vice versa, that it is capable of overcoming the effects produced by atropine. The first symptom noticed is dimness of^ distant vision, and shortly after the pupil becomes contracted; the symptoms also subside in the same order, first the derangement of accommodation, and tlicn the affection of the pupil. Let me now say a few words as to the method of action of tlie Calabar bean. In respect to its effects on the pupil they might be produced either by causing contraction of the circular fibres of the iris, or by paralyzing its radiating fibres. I am inclined to believe that the contraction of the pupil is due to increased action of the sphincter pupillfe, and this chiefly on the ground that the other effects produced by the Calabar bean can only be explained by an induced contraction of the ciliary muscle—the muscle of accommo- dation ; and as the sphincter pupilla^ and ciliary muscle are both supplied by the ciliary nerves, I tnink the most feasible ex])lanation of the action of the Calabar bean on the eye is to regard it as a stimulant to the ciliary nerves. In favour of this view we have the feeling of straining in the Qjc shortly after the physiological effects are produced. The alteration, too, in the accommodation of the eye exhibits much of the character of a spasmodic action; thus