Heterophoria of some kind or degree may be found in nearly every person, and frequently a very high degree be present without causing any disturbance. In all such cases when the patient is not suffering from eye-strain or any reflex symptom no treatment for the heterophoria should be undertaken.
The Operation of Graduated Tenotomy, as suggested and practiced by Stevens, is as follows : Three or four instillations of a 4 percen solution of cocaine should be made at intervals of four or five minutes, the eyelids then being separated with a speculum, a fold of conjunctiva exactly over the center of the insertion of the muscle is seized, and with the scissors a transverse incision not exceeding one-half of a mm. in length is made through this membrane with the forceps, pressing the outer cut edge of the conjunctiva backward, the tendon of the muscle is seized in its centre a little behind its insertion and divided with the scissors. The delicate Stevens’ hook is then inserted through this opening in the centre of the tendon and the opening enlarged by careful division of the tendon toward the borders until the desired effect is acquired. Under cocaine the patient experiences no pain, and the extent of the operation is regulated by frequent examinations with the phorometer. If too extensive, it may be limited by a very fine suture inserted through the centre of the divided muscle and through the conjunctiva at the inner side of the wound and tying it only sufficiently tight to have the desired effect.
Stevens’ Advancement Operation.- The eye is cocainized and the conjunctiva opened as in tenotomy. The tendon is seized with the fixation forceps at the exact center of its attachment to the sclera and a free tenotomy made. The forceps remain attached, or a silk loop is passed through, to hold the tendon and to act as a guide to its exact centre. The tendon is then drawn out and the connective tissue between it and the conjunctiva loosened. When the tendon has been drawn out sufficiently to reach the point desired for its new attachment it is seized at that point by a fixation forceps, and a V-shaped piece cut out with the apex toward the new attachment of the forceps. A fine, but strong suture is now passed sufficiently behind the forceps to insure a good hold, and then through the conjunctiva and some of the sclera near to the cornea and tied. The patient should be tested with the phorometer immediately after the operation and the aim should be to secure a few degrees of excess over the actual amount required, as usually several degrees of effect are lost during the first forty-eight hours owing to stretching or partial cutting out of the suture. It is always well to cover the eyes for one or two days after an advancement to prevent traction upon the suture until some degree of new adhesion has taken place.
As already stated, however, the operation, we believe, should be held as a dernier ressort, and treatment first directed toward increasing the power of the weaker muscle. This is best accomplished by the use of prisms to exercise and strengthen the muscle, precisely on the same theory as other voluntary muscles of the body are strengthened by the use of dumb-bells, exercise in the gymnasium, etc.
In hyperphoria my practice is to give the patient prisms, set in spectacle frames, with the base up in one eye and down, in the other of sufficient strength to cause vertical diplopia with the images near together. These are to be worn daily for from ten to twenty minutes, after the double images are fused while looking at objects in the room and at greater distances. The strength of the prisms are increased from time to time, as the superior and inferior muscles gain power and are able to overcome the prisms. The degree of the hyperphoria should be tested frequently to learn when to stop the exercise, that it may not be overdone. I have found in some cases that an ability to overcome prisms of 12 degree (a prism of 6 degree base up in one eye, and of 6 degree base down in the other) can be acquired by this exercise, but usually they will be only able to overcome prisms of from 5 degree to 8 degree; and oftentimes the hyperphoria will be corrected when even a power to overcome a weaker prism than this is acquired.
In esophoria precisely the same method is followed, but of course with the base of the prism set in, toward the nose, before each eye. In this exercise a power of overcoming prisms of from 12 degree to 16 degree (divided between the two eyes) is usually obtained, and as high as 24 degree has been acquired.
In exophoria my method of exercising with prisms is entirely different. For this, prisms one and half to two inches square are used. The patient is seated from fifteen to twenty feet from a lighted candle, a prism of sufficient strength to produce horizontal diplopia with the images near enough together to be readily fused, is then held with the base out before one eye, by an effort of the patient the lights are brought together and held one for a moment, when this is removed and a stronger prism placed before the eye. This procedure is followed, using stronger and stronger prisms, so long as the eye can fuse the images; then the other eye is put through the same training, and the exercise should then cease for that sitting. My experience has been that the best results are gained in exercising the internal recti every other day; that they will usually gain from 2 degree to 10 degree at each sitting, and should always be exercised to the same degree at least as the previous sitting, in order to hold all gain that is made. The prisms should always be held so that the images are on the same level, else they cannot be fused. In some cases it is necessary to use a red glass before one eye, so that the patient can more readily recognize the two images. In low degrees of exophoria the patient should always be exercised by the surgeon; but, where there is considerable exophoria, he may be ordered a set of prisms, shown how to use them and carry out the exercise at home, but always under the direction of the surgeon. My usual directions are to exercise up to a certain degree, when they are to report for examination; if exophoria is still present, they are allowed to go on to a still higher degree, and so on. The power of the internal recti to overcome prisms is readily increased in nearly every case to up ward of 60 degree and in the majority to upward of 70 degree.
Results from exercising with prisms are always more prompt and satisfactory in cases of exophoria than in either hyperphoria or esophoria, as the internal recti, having much greater power normally, seem to respond more readily to the systematic exercise.
Prisms may also be used for another purpose, viz : To correct the heterophoria. In this case they serve as a crutch to remove the strain from the weaker muscle. In prescribing prisms for this purpose it is better, as a rule, not to put on the full correction of the heterophoria, and they should not be ordered at all until after the prismatic exercise had been carried to its full extent without relief. They should, however, as a rule be worn in preference to an operation, for after their use for some time the muscles may regain their normal balance and the prisms be discarded. Very flattering results have followed the wearing of even a 1/2 degree prism.
In all cases the refraction should be carefully examined, and usually it is necessary to make a through examination under atropine. If any error is detected, it should be as carefully corrected, for an uncorrected refractive error is undoubtedly the cause, in many cases, of the heterophoria, and its correction will often cure the heterophoria without other treatment. The muscular equilibrium should be especially examined, while the glasses to be used both at distance and in accommodation are on, before prescribing them because convex glasses will increase exophoria and diminish esophoria. Many cases of esophoria associated with hyperopia will be wholly corrected by the use of the proper convex glass, which should be as nearly as possible the glass which causes orthophoria both in distance and in accommodation. On the contrary, in exophoria associated with hyperopia the weakest glass possible, or none at all, should be prescribed. Concave glasses will have an opposite effect on exophoria and esophoria to that of convex glasses. Examination of hyperopic eyes under atropine will always show a much higher degree of hyperopia when esophoria is present than when there is exophoria, and hence stronger convex glasses should always be prescribed in hyperopia when esophoria is present than where there is exophoria.
It is, therefore, important to always test the muscles with the eyes in the state they are to be used, viz., with their glasses on.
The effect of glasses for refractive errors on heterophoria can be aided by either combining prisms or by decentering the lenses; the decentering of the lens gives the same effect as the combination with prisms without the annoyance of the additional weight. As a rule, but a very low degree prism can be worn for distant vision. The effect that can be secured by the decentration of lenses is also very limited varying, of course, with the strength of the lens.
Professor of Ophthalmology in the College of the New York Ophthalmic Hospital; Surgeon to the New York Ophthalmic Hospital. Visiting Oculist to the Laura Franklin Free Hospital for Children; Ex-President American Homoeopathic Ophthalmological, Otological and Laryngological Society. First Vice-President American Institute of Homoeopathy : President Homoeopathic Medical Society of the State of New York ; Editor Homoeopathic Eye. Ear and Throat Journal : Associate Editor. Department of Ophthalmology, North American Journal of Homoeopathy, etc.