SYMPTOMS.- This condition is apt to cause far greater disturbance than any other variety of heterophoria. A greater or less degree of amblyopia is, according to Stevens, found in a larger percent. of the cases of hyperphoria, and is by him attributed to suppression of images, owing to the inability of the muscles to maintain the two eye on the same horizontal plane. Spasmodic closure of the lids and involuntary contraction of the muscles of the face may be present. The head is apt to be carried toward the shoulder. Constitutional effects, such as neuralgia, headache, persistent nausea, pain in the back, vertigo and neurasthenia have undoubtedly been caused, and relieved by the correction of an existing hyperphoria. Examination as to the power of the muscles in overcoming prisms with the base up or down should always be made. The usual strength in normal eyes will vary from 3 degree to 8 degree, and I have found those who could fuse the images through a prism of 12 degree with the base up or down.
Esophoria.- Is a condition of insufficiency of the external recti muscles or a tendency to convergence of the visual lines. The method of determining esophoria has been already described, but quite frequently examination reveals an esophoria at the distant point and exophoria in accommodation. In such cases the presence of hyperphoria should always be suspected.
Esophoria as a cause of muscular asthenopia has received but very brief attention in text-books upon ophthalmology, and yet that it can and does cause many annoying cases of asthenopia is now being recognized by the advanced thinkers in this department. Noyes (loc. cit.) states that out of 100 consecutive cases of muscular asthenopia, 74 were cases of insufficiency of the external recti (esophoria).
Stevens states (loc cit.): ” In respect to the clinical importance of esophoria, which occurs in the proportion of more than three to one of exophoria (this has been modified in a later article by Stevens to a proportion of two to one), it plays a much more important role than the latter as a predisposing cause to a variety of neuroses; and, as the immediate cause of asthenopia and kindred affections about the eyes, it is an element of great disturbance.” My own experience, however, has shown a larger proportionate percent. of cases of exophoria than has been found by the authorities quoted. This difference has probably been due to the fact, that it is sour practice to base the diagnosis, in those cases frequently met with, in which there is found esophoria at the distant point and exophoria in accommodation, upon the condition which seems to be creating the most disturbance. That is, if the asthenopic symptoms are only caused upon use of the eyes at the near point, the case then, we believe, should be considered one of exophoria; and if the distress occurs after use of the eyes at distant vision, one of esophoria. We believe, oculists generally base the diagnosis upon the results found from examination at the distant point alone, and too frequently ignore the loss of muscular equilibrium in accommodation.
SYMPTOMS.- The disturbing effects from esophoria are more obscure and remote than in exophoria. The patient affected with esophoria is apt to suffer from headaches at the back of the head and neck, a general sense of illness, nausea, vertigo, etc., on the day following a visit to a picture gallery, an attendance at church or theatre, from driving or riding on the cars, in fact from any use of the eyes to maintain parallelism of the visual lines at distant objects. While in exophoria the patient is more apt to suffer with pains in the eyes or head immediately after one or two hours use of the eyes for reading, sewing, etc. There is often a weakened power of accommodation, with dilatation of the pupil present. They often complain of the annoyance of seeing their nose, or of seeing a black spot before their eyes. Amblyopia is the rule in cases of esophoria exceeding 2 degree (Stevens). Esophoria is found to be almost invariable of a higher degree when the eyes are under atropine.
Examination as to the power of the external recti muscles in overcoming prisms base in shows the average strength to vary from 10 degree to 14 degree, yet an abduction of 6 degree may not be incompatible with orthophoria. In some cases of esophoria I have seen a power acquired overcoming prisms of 24 degree base in, and still an examination would reveal esophoria.
Exophoria.- Insufficiency of the internal recti, or tendency of the eyes to divergence, is, we believe, in spite of the experience of others, the most common form of muscular disturbance. This, it would seem natural to expect, especially in the educated classes, from the constant over-use of the internal recti at the near point.
SYMPTOMS.- In exophoria we find the most characteristic symptoms on using the eyes, the pains are generally in the eyeballs, the patient wants to rub and press them for relief. Often a blurring, of the vision; the letters seem to run together. The headaches occur especially after using the eyes for near work, and are more often frontal, but may be in any part of the head. The power of accommodation in exophoria, contrary to that in esophoria is usually increased; this is owing to the relation existing between convergence and accommodation, the insufficiency of the internal recti demands and results in greater action of the accommodation. Examination of the powder of the internal recti for overcoming prisms will, like the other muscles, give most variable results; in some cases orthophoria will be established when an adduction of 20 degree is reached, but usually an adduction of upward of 70 degree will readily be acquired by a little exercise. I have also seen an adduction of 80 degree reached in many cases, and the tests still showed an exophoria.
HETEROPHORIA AND ITS TREATMENT.- The definition of heterophoria, as given by Stevens, of an abnormal adjustment of the eye muscles, or a tending of the visual lines in some other direction than parallelism, applies as well to strabismus, and the difference between the two conditions must be borne in mind. In heterophoria binocular vision is habitually maintained, but by the expenditure of a greater amount of force than is demanded in the perfect equilibrium of the ocular muscles. In strabismus there is, on the contrary, habitual diplopia, though, as a rule, the subject, by long suppression of one image has become unconscious of it. Therefore, the dividing line between heterophoria and strabismus should rest on the habitual ability or failure to maintain binocular vision.
In no ophthalmic disorder has it been found so necessary to individualize the case as in muscular insufficiency. Sometimes the highest degrees of heterophoria may be present without asthenopic symptoms, headache or nervous disturbances, while, upon the other hand, the lowest degree may give rise to an aggravated train of symptoms.
Locomotor ataxia, chorea, epilepsy, acute mania and other mental disorders are claimed and undoubtedly have been cured, in some cases, through correction of the heterophoria.
When we come to consider the delicate mechanism of the eye and the important part that the ocular muscles perform in the carrying out of the function of the organ, one must become convinced that any insufficiency on their part may serve to create various asthenopic symptoms, headaches, neuralgias and reflex nervous disturbances. We must, however, decry the tendency of some enthusiasts to attribute all ills that flesh is heir to, to heterophoria.
As regards the treatment of heterophoria we wish to reiterate our statement of six years ago, viz.: We desire first to most emphatically protest against the too prevalent operation of graduated tenotomies. While graduated tenotomies are still being made as frequently as ever by a few enthusiasts, specialists as a rule now only resort to operative measures in exceptional cases. It is to be sure far more brilliant to give the sufferer relief by operative measures than by a more or less tedious course of treatment, but have we the right to permanently lame or weaken the power of any muscle so long as the desired end, relief of the patient, can be attained by any other method? In all forms of heterophoria there is either an insufficiency of one muscle or a preponderance of strength in its opposing muscle, and in order to secure relief the normal equilibrium between these two muscles must be restored. It seems to the writer more rational to consider the mass of cases to be the result of a muscle weakened by overuse, rather than a faulty insertion, or an abnormal strength of the opposing muscle. The theory of tenotomy is to weaken the action of the stronger muscle so that the normal balance between it and its opposing muscle may be re-established. The theory of treatment is to strengthen the weaker muscle and thereby re-establish the normal balance. In either method the proper equilibrium is restored; in the first plan by means of two weakened muscles and in the latter by two strong muscles. I have seen many cases where tenotomies have given prompt and marked relief for a time, but in six months or a year they have fallen back into an even worse state than at first. I do not wish to be understood as claiming that no case requires operative treatment, for some of them can only be relieved by operation; but first the weaker muscle should be strengthened to its utmost limit, and then, if relief is not given and the normal balance not restored, an graduated tenotomy may be made.
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.