Homatropine is an oily liquid produced by the action of muriatic acid on the cyanate of atropine. With hydrobromic acid it forms a readily crystallizable salt, the solution of which acts on the eye like atropine, but more promptly and transiently. One drop of a solution of one to one hundred and twenty, usually gives in twenty minutes, full pupillary dilation and complete paralysis of accommodation which lasts only for twenty-four hours. Add to this that there is little danger of constitutional disturbance and poisoning, and homatropine must be accepted as a more desirable agent than atropine. It is especially to be preferred in cases of senility with shallow anterior chambers, and in glaucoma, in which atropine tends to aggravate the lesion.
Daturine, the alkaloid of datura stramonium is a potent mydriatic, causing pupillary dilatation in a solution of one to one hundred and sixty thousand of water. It appears to be identical with atropine.
Duboisine the alkaloid of duboisia myoporoides is also a potent mydriatic. Jaarsma found that a solution of the sulphate, of one to three thousand, paralyzed accommodation for twenty-four hours. It acts more promptly than atropine but is more poisonous.
Hyoscyamin, the alkaloid of hyoscyamus niger, is also strongly mydriatic. One drop of an one to three hundred solution of the sulphate paralyzed accommodation for from seventy-five to one hundred hours. Risley found it to act more promptly than atropine, and to be less dangerous than duboisine.
WOUNDS OF THE EYELIDS.
Traumas: bites, lacerations, blows, penetrating wounds, gunshot, scratches, kicks. Upper lid or commissure. Reparatory power of eyelid. Danger of distortion. Treatment: sutures, plaster, shellac, collodion, gelatine, Frick’s gelatine, birdlime, sterilisation: Quilled and twisted suture. Position in stall. Metallic guard for eye.
Causes. Traumatic injuries of the eyelids are especially common in the horse mainly because of his exposure in connection with the services required of him. In a team he is liable to be bitten by one of his fellows, or the lid may be caught on nails, in turning, or on hooks upon harness, chains or wagons. It is sometimes injured by a blow from a club or whiplash, or by knocking the head against solid objects that he failed to see on account of the blinds. Again the injury will come from running against prongs of bushes or trees, or of stump fences. Occasionally a blow with the horn of an ox or cow is the cause, but this is much more frequent with the bovine races. Then again gunshot wounds are found in all animals. In sheep the eyelids sometimes suffer from bites of dogs, while in dogs and cats, the teeth and claws are the main causes of injury. These smaller animals also suffer from brutal blows and kicks.
Nature. Wounds of the eyelids almost invariably affect the upper lid, because of its extra size and prominence. Sometimes one commissure or the lower lid is the injured part.
Clean incised wounds are rare, while lacerations with or without contusions are the common experience. The laceration often extends through the free margin of the lid, and then to one side, mostly the outer, in a direction more or less parallel to the tarsus. The result is that the detached flap drops downward exposing a greater or less portion of the bulb covered with blood. The conjunctiva, the cornea, the sclerotic or iris may be implicated in the lesion in different cases, so that such wounds are of the most varied degree of gravity. If, however, the lesion is confined to the lid, and in the absence of absolute detachment of the flap, or severe contusion, a good repair may be confidently hoped for. The vascularity and reparatory powers of the eyelid are unusually great, and the looseness of the skin, connective tissue, mucosa, and even the muscles is such that they do not draw injuriously upon the edges of the wound to disturb the process of cicatrization. If the two opposing ends of the divided tarsal cartilage are kept in accurate opposition, the elasticity of his structure serves to preserve the even contour of the palpebral margin, and the adhesion or granulation process between the edges of the wound, soon becomes firm enough to prevent further displacement. Even when one-half of the eyelid is torn loose, remaining attached only by a narrow portion, reunion without any unsightly distortion is not to be despaired of. In case of a mere vertical laceration on the other hand, the case is very simple and hopeful. Even when a portion of a lid has been completely torn off and lost, the loose textures of the remaining part, often appear to stretch in the process of healing so that a fairly serviceable, though by no means an æsthetic covering for the eye may remain. This may serve for a common work horse, but the unsightliness would necessarily debar him from use in a carriage or as a saddle horse. The imperfect protection too, exposes the eye to rainstorms, hail and snow, as well as to dust, and greatly predisposes to conjunctivitis.
Treatment. One can trust implicitly to the extraordinary reparatory power of the eyelids, yet so unsightly is any distortion of these parts, that the greatest pains must be taken to obviate loss of substance, or unevenness or puckering in healing. The points to be mainly sought for are the perfect coaptation of the divided edges, and the restraining of the patient from interrupting the healing process and breaking loose the forming adhesions, by rubbing the eye.