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In heterophoria, the success of the operation depending on a partial or accurately measured tenotomy, local anesthesia is essential. Indeed, a precise operation cannot be performed unless the patient is conscious and can advise during the procedure of the effect obtained by the various steps.
In heterotropia (or true strabismus) general anesthesia will be frequently necessary. Operations for convergent strabismus are oftenest done on children under twelve years of age and there are few children who are stoical enough to bear the procedure under local anesthesia whether the operation be tenotomy or advancement. This is always a disadvantage in that the normal coordinations are set aside by the general anesthetic and the eyes drift outward and upward into the position normally assumed during sleep. Under these circumstances one can form no judgment as to the amount of surgical correction necessary, and will have to be guided entirely by previous experiences as to how much to tenotomize, how much tissue to remove, or how far to advance a tendon in a given case.
In adults many operations (even advancement) may be done under local anesthesia, especially if conjunctival and subconjunctival anesthesia are combined.
Ordinary conjunctival anesthesia is obtained by instilling one or two drops of whatever anesthetic may be used every three minutes for five applications. This will suffice in all tenotomies done without the strabismus hook and in some done with the hook. In the latter method, however, the patient often complains of much discomfort when the muscle is lifted on the hook. Indeed it is the most trying period in the operation. We have found that the use of an anesthetic subconjunctival^ after conjunctival anesthesia .has been produced contributes greatly to the patient's comfort. The following solution is used:
4 per cent. sol. cocaine muriate, i fluiddram.
Solution adrenalin, 1 : 2000, 1 fluiddram.
of which 5 to 8 minims are injected with a hypodermic needle under the conjunctiva over the muscle or muscles to be attacked. During the ten minutes wait for this solution to act, gentle continuous pressure is made on the eye wth a gauze pad to so diffuse the introduced liquid that it will affect the widest possible area and also to disturb as little as possible the natural topography of the parts. The operation may then be approached with fullest confidence and with a comparatively bloodless field because of the adrenalin preparation. In many adults, if they have any pluck at all, advancements may be done almost painlessly by this method. The advantage of having the patient conscious with the normal innervation to the eye-muscles during such an operation cannot be overestimated. Without subconjunctival anesthesia, relatively few advancements can be performed even on the most phlegmatic adults. Naturally other anesthetics such as holocain hydrochloride, novocain, alypin, stovaine, or beta eucain may be employed, but some adrenalin preparation should be used with them whether the anesthesia be conjunctival or subconjunctival. We have used beta eucain with much satisfaction. It cannot be too much emphasized however, that in children under twelve to thirteen general anesthesia will almost invariably be required.
ANTISEPSIS. ASEPSIS AND INSTRUMENTS.
The operator's hands and nails should be scrubbed with warm water and soap until all mechanical impediments to the action of the chemical agent to be used immediately afterward are completely removed. The hands are then dipped in a solution of bichlorid, biniodid, or cyanid, of mercury, 1 to 3000. The skin of the patient's face in the neighborhood of the eye is scrubbed with warm water and soap, then douched with normal salt solution, and washed finally with 1:6000 mercurial solution. In this manipulation, particular attention must be paid to thorough cleansing of the eyebrows and lashes. The conjunctival sac and the conjunctival surfaces of the lids are flushed with physiologic salt or saturated boric-acid soluton, and fresh cocain solution is applied. The instruments are first placed in boiling water and then in alcohol, where they are allowed to remain until used. This simple method of treating the instruments is sufficiently germicidal for all operations where the field is not unusually septic.
The object of tenotomy is two-fold: By altering the tendinous attachment of a muscle to change its mechanical relations to the globe and to the other muscles, and by thus lessening the power of the muscle to so influence the distal response to innervation, that equilibrium and coordination shall be inaugurated or reestablished; second, to develop or restore symmetric and corresponding nerve-excitation. We are concerned, first, with the muscle or muscles at fault, and, second, with the degree of deviation—i. e., whether there shall be partial or complete muscledivision, and whether it shall apply to one or both eyes.
In heterophoria, unless there is good ground for believing that one muscle is abnormal either in structure or insertion,the operation should in all cases be divided between the two muscles, relieving an equal amount of tension in each. In heterotropia (esotropia for instance) the evils resulting from extensive tenotomy in one eye for high grade deviation are limited movement nasalward, diplopia in the periphery of the field, cicatrization of the conjunctiva and capsule at the site of the wound, retraction of the caruncle and protrusion of the eyeball. In monolateral strabismus with high grade amblyopia it is our practice to do a moderate tenotomy of the internus and extensive advancement of the externus of the deviating eye. Later, if necessary, advancement may be done on the externus of the sound eye. The same principles obtain in exotropia, save that the muscles to be attacked are of course reversed. In esotropia or exotropia without well marked amblyopia, advancement of both externi or interni (as the case may be) is the operative procedure of election.
Fig. 73.—Instruments used in tenotomy, a, scissors; b and c, tenotomy hooks; d, speculum; e, conjunctival forceps.
After insertion of the speculum or separation of the lids by an assistant (lid elevator held in one hand and the lower lid depressed by a finger of the other hand) the conjunctiva and the capsule lying immediately over the insertion of the tendon into the sclera are firmly grasped by the single tooth conjunctival forceps.