HETEROPHORIA may be defined as that condition in which binocular vision, being temporarily suspended, the visual lines of the two eyes do not intersect at the point of fixation. It is characterized by a change in the innervation of the ocular muscles when the binocular fusion of images is prevented. Under normal conditions, binocular vision for a given point is, maintained by the co-ordinate action of the entire group of these muscles, and in the ideal eye, at least within certain limits, the innervation of these muscles is not a necessary function of the binocular act. That is to say, the binocular fusion of images being suspended, the innervation remains unaltered. It becomes a function of this act only in states of heterophoria.
Heterophoria is due essentially to a condition of faulty innervation, which depends upon one or more of the following factors:.
1. The form and position of the eyeballs (orbits).
2. The place of insertion of the ocular muscles.
3. The essential and relative power of the ocular muscles (amplitude of convergence).
4. The ratio of the positive and negative portions of the relative accommodation, together with the ratio of the convergence and accommodation for the point in question.
Under the first head it is clear that, assuming certain ratios of tension among the muscles of the eye as normal when fixing some point at a given distance from the eye, such as 1 m. for example, these ratios must vary with the length of the basal line of the eyes. For at this distance, with a basal line of 50 mm., the angle of convergence is 1.43 degree, while with a basal line of 75 mm. it is 2.15 degree. In high degrees of myopia the alterations in the form of the eyeballs limit their mobility, and, consequently, modify the convergence tension of the muscles.
There is some variation in the place of insertion of the ocular muscles. Stilling has observed a wide variation in that of the superior oblique. We may assume as normal the following measurements, representing the distances of the insertion of the recti muscles from the cornea (Fuchs):.
Rectus internus, 5.5.
Rectus externus, 6.9.
Rectus inferior, 6.5.
Rectus superior, 7.7.
In an eye where the muscular balance is ordinarily good, one or more muscles may become weakened by fatigue or disease, necessitating an increase in the amount of nervous stimulus to these muscles in order to preserve binocular vision. Under these circumstances, if binocular vision becomes abrogated, heterophoria is an easy and necessary consequence. Here we have true “muscular insufficiency.”.
From the essential connection of accommodation and convergence, it is evident that the ratio of the positive and negative portions of the relative accommodation for any given point has an important bearing upon the muscular balance for that point. Indeed, if no other factor were operative to affect the muscular equilibrium, it seems reasonable to assume that it could be calculated from a knowledge of the relative accommodation. However, as a matter of fact other causes uniformly do exert an influence upon the position of the eyes, and moreover may be of such moment that their effects entirely negative that of the relative accommodation.
We see, then, that heterophoria may originate in a number of ways. From the variety of causes we may infer that there must a corresponding variation in the treatment of this disorder. We shall revert to this further on.
Methods of Examination.-In ascertaining the amount and character of the heterophoria present in a given case, the essential determination to be made is the position of the non- fixing or deviating eye. The common and most exact methods of making this determination are subjective. of objective methods, the only one that is practical is the old test of alternately covering and uncovering one eye with a screen. This is too crude to be of much value. Subjective methods depend upon the uniformity and congruity of retinal projection. The first instrument of precision for making the necessary measurements was Stevens’s phorometer.
With this instrument, supposing the patient to be of ordinary intelligence, it is possible to measure deviations of the eyes in any plane with much accuracy. The substitution of a “stopped” convex lens of short focus for the vertical and horizontal prisms employed as to the character of the deviation could be made. The “red test” of Maddox marked another gain in the rapidity of the examination, and made it possible to measure the deviation of the non-fixing eye by means of scales drawn upon the wall of the examining-room. Burnett’s use of a strong convex cylinder was based upon the same principle. Another gain in convenience and precision was the introduction of the rotating prisms of Stevens, by which the separate displacing prisms were done away with. I have added another instrument to this number, a rough model of which I have the pleasure of exhibiting to this section.
It consists essentially of a frame, holding upon its right side a cell containing two 6 degree prisms, with their bases in contact; or a Maddox rod, suitably mounted; and on the left a “prism mobile” of two 5 degree prisms, which, by suitable mechanism, may be rotated in the same or in opposite directions, and the amount of rotation measured upon a graduated circle so placed as to be easily seen by the observer. Behind the openings of this frame or slide are clips for holding various accessories, such as abducting or adducting prisms, a red glass, etc. With the double prism in proper position, and the “prism mobile” at 0 degree, set to give horizontal displacements, the patient looks at the point of light through both openings and sees three images of it.
The middle image is seen by the left eye, and by turning the milled head of the “prism mobile” it may be displaced horizontally either to the right or left, from 0 degree to 10 degree. If, therefore, this image is not in a straight line with the other two, it may be quickly brought into this position, and the exophoria or esophoria read of at once upon the graduated circle at the patient’s left.
To measure deviations in any other plane, the double prism is rotated into that plane, the “prism mobile” brought to zero, the small milled head in the face of the instrument pushed well up, and, the pinion of the recording disk being pulled out, the two prisms are rotated by means of this milled head in the same direction to the desired angle, when these adjustments, being reversed, the measurements are made in the same manner as at first. A little familiarity with the instrument will enable the observer to make these adjustments very rapidly.
The Maddox rod may be substituted for the double prism if desired. To measure heterophoria greater than 10 degree, a supplementary prism may be inserted in the proper position in one of the rear clips, and its value added to the readings of the instrument.
To measure abduction and adduction, or in fact, muscular power in any direction, the double prism or rod is removed from the right-hand cell, and the “prism mobile” having been set in the desired position, the muscular powers can be easily found by rotation of the milled head at the left. In these determinations also, supplementary prisms may be inserted into the clips if necessary.
It will be seen that a considerable variety of measurements may be made by this instrument with rapidity and accuracy. Almost any object of fixation may be used, and at my distance from the eyes. The value of the double prism is, that it is easier to determine whether three points are in the same straight line than whether (as in Stevens’s phorometer) two points are in an exactly horizontal of vertical line, as the case may be. I believe that the credit of suggesting this use of the double prism is due to Savage, although the first model of this instrument was made long before his suggestion came under my observation.
So far as accuracy is concerned, there is a substantial agreement in the results obtained by the use of the Stevens phorometer the rod test, and the little instrument above described. Bissell has made a serious of comparisons of the rod and prism tests. In fifty-two cases of heterophoria, the findings of the rod test were greater than those of prism test in twenty- six, the difference ranging from 0.25 to prism dioptries, from which he concludes that the rod test is the more accurate. I do not believe that this accords with the experience of observers generally.
For the determination of “insufficiencies of the oblique muscles,” Savage employs the double prism before one eye, and a horizontal stripe at a distance of eleven inches, as a test object. If there is an insufficiency present, the middle line will run obliquely between the other two, the direction of the obliquely being dependent upon the particular muscle at fault.
Heterophoria may be measured in degrees of refracting angle, or of minimum deviation; in prism dioptries, in metre-angles, or in centigrades. The most common method is to use the refracting angle of the necessary prism. There is at present, no agreement among oculists as to the most desirable of the various reforms that have been suggested.
Symptoms.-In attempting to enumerate the symptoms of heterophoria, are we enter at once upon debatable ground. A wide difference of opinion prevails among physicians as to the symptoms which heterophoria is capable of setting up. On the one hand is a class of enthusiasts who claim for this disorder the power of exciting numerous, remote and performed alterations in the functions of the nervous system, extending its effects to include chorea, epilepsy and insanity. In support of this claim, clinical experience in these affections is set forth, showing that they have sometimes been relieved by proper treatment directed to the heterophoria alone.
On the other hand there are those who deny these claims in toto and presumably upon scientific grounds. It is difficult to deny the evidence of one’s own experience, or that of other competent observers, but it is not always easy to interpret clinical facts. So far as concerns the cure of remote disturbances of the nervous system, such as epilepsy, for example, by the performance of graduated tenotomy, it must be borne in mind that in idiopathic epilepsy at least, patients have often recovered as an apparent result of a variety of surgical operations, such as trepanation without discoverable lesion of the brain our meanings; circumcision for phimosis; the excision of scar tissue; the removal of bullets, and many other diverse procedures.
It is of the greatest importance to observe the fact that there is often a curative influence in a purely indifferent surgical operation. Thus we have recorded cases where, independent of the direct and proper results of the operation, abdominal tumors of considerable size have disappeared after a simple incision of the abdominal walls, and hip-disease has been cured, it is said, by removal of the fore-skin. Even without the hypothetical effects of trauma upon the nutrition, functional and organic diseases have not infrequently, I think, been cured simply by some radical change in the patient’s emotional state.
My attention has just been called to a case of cataract reported as cured by “Christian Science.” From the accumulated evidence now at hand, I believe that hardly more can be affirmed than that these remote neuroses may in rare instance be among the symptoms of heterophoria, but that their claim to such a place has not yet been established beyond cavil.
Sequin has recently given a provisional statement of the symptoms of certain forms of eye-strain. According to this writer, paresis (insufficiency) of the third cerebral nerves and attached muscles (in which condition we may get exophoria or hyperphoria or both) is marked by certain rather definite symptoms, of which he regards occipito-cervical pain and distress as the most characteristic. “The pain,” he says, “diurnal, as a rule, and often not appearing until the patient has used his eyes in dressing, eating or reading, is usually greatest between the occipital bone and the second vertebra, though if often extends from the upper part of the occiput to the fourth or even sixth vertebra.
It is sometimes more a ‘distress’ than a true pain, and is often accompanied by sensations of stiffness and tightness (‘as if a hand grasped the neck’). There is never, strictly speaking, neuralgia of the occipital nerves, or objective rigidity, as in beginning caries. Tenderness is rarely found, though in women spinal hyperaesthesia (so-called spinal irritation) often coincides. Frequently there is a sensation of weight or downward pressure on the back part of the head, with (usually) intermittent numbness (a ‘dead’ or ‘wooden’ feeling) and formication. In some cases the fulness or rightness (cincture or cap feeling) extends to the whole head.
Apparent loss of power of attention and concentration (volition) is much complained of, even to a degree simulating mental failure. Reading, writing sewing piano practice, conversation, even eating, are painful or unbearable; in other words, the symptoms are increased by any act requiring convergence and accommodation. The prolonged duration of these symptoms, or, rather, of the strain, may lead to neurasthenia, insomnia and a curious mixture of hysteria and hypochondria, so that the diagnosis becomes more obscure.
Headache is not rare, but in such cases there are also faults in refraction or other factors. Simple asthenopia, sense of fatigue, or pain in the eyes, orbits, brow or temples, is only occasional, and seldom a prominent symptom. Usually the patient pretends to have strong eyes.”.
Payne has recorded a some what similar classification, referring the occipital headache to exophoria and hyperphoria. He adds the additional symptoms that these patients show marked inability to use their eyes at night, while their ordinary use in the daytime is comparatively easy. Frontal pain or headache is referred to excessive strain of convergence or accommodation, as in hyperopia and astigmatism.
The symptoms of esophoria are less clearly marked. Seguin notes, as associated with paresis of the “sixth cerebral nerves,” that a sense of confusion, or dizziness, not a true vertigo, is one of the most prominent symptoms. The use of the eyes for distant objects, walking in the streets, contract and business with other persons, attendance at church or in the theatre, sight-seeing, shopping and similar occupations may be productive of great distress to the patient, who feels better when quiet and alone.
“Various and peculiar sensations are felt in the head, such as a sense of fulness, ‘as if the head would burst;’ a downward pressure on the head, diffused or localized, ‘as if a stone or sharp stick’ pressed on it; a sense of constriction, general or cincture-like; pain in various areas of the scalp; occasional feelings of numbness )a ‘dead’ or ‘wooden’ feeling), or of formication or worm-like crawling, also variously distributed; a quasi-tinnitus, or noise in the head (not in the ears) is not rare.” (Seguin.).
The symptoms of esophoria are not so characteristic as those of exophoria and hyperphoria, and will be seen to overlap them.
Insomnia and general nervous debility are said to be not uncommon results of continued eye-strain. In the eyeball itself there are reasons to believe that various forms of local inflammatory affections, such as conjunctival hyperaemia, blepharitis, ulcers, etc. (Stevens), may sometimes be indirectly dependent upon eye-strain. Stevens has called attention to certain facial expressions characteristic of the various forms of heterophoria. In esophoria, for example, the brows are compressed, with the inner end curving down toward the nose; lines upon the forehead low. In exophoria the brows are raised or arched; lines upon the forehead high. In hyperphoria the features are more irregular, and one eyebrow is compressed or drawn down, to correspond with the hyperphoria.
Treatment.-Here, again, we enter upon a subject where widely different opinions are held. In approaching the question of treatment we must not fail to bear in mind the various causes which may lie back of the heterophoria. I am convinced that an intelligent appreciation of the causation in a given case, where possible, will often lead to a more just treatment than could be given by any manner of routine.
It is true that it is often impossible to ascertain the cause in a given case of heterophoria with any exactness, but even a reasonable inference is highly desirable. Thus, in a case of exophoria due to paresis of the internal recti from general debility or overwork, it would be manifestly improper to resort to tenotomy for its correction, while if it were due to the anatomical changes in the eyeball incident to a high-grade myopia, the surgical procedure might be eminently proper.
The treatment of heterophoria should begin with the determination of the following points:.
1. The amount and character of the heterophoria; a, for infinity; b, for reading distance: i,e, 1/3 metre.
2. The mobility of the eyeballs in various directions.
3. The refraction.
4. The muscular power; a, adduction; b, abduction; c, circumduction; d, amplitude of convergence.
5. The relative accommodation; a, for infinity; b, for reading distance.
The practical value of these determinations evident. That of the relative accommodation will be necessary or at least useful, in certain cases only. The amplitude of convergence may be determined by means of Landolt’s ophthalmo-dynamometer, for its positive, and abducting prisms for its negative portion. The information which it supplies is largely contained in the determinations of the abduction and abduction. Thus if the negative convergence-abduction in a given case is markedly defective, tenotomy of the internal recti muscles for exophoria would be inadmissible.
Hyperphoria.-Stevens states that the treatment for hypendhoria is tenotomy. This statement is in accord with my own experience. In some cases, where there is an error of refraction requiring the constant use of glasses, a correcting prism may be incorporated with them, and give satisfactory relief. Or with emmetropic eyes, the prism may be mounted in spectacle frames and worn constantly.
It is questionable what internal remedies can do for the relief of hyperphoria. The late Geo. S. Norton, M.D., in 1889, called attention to the provings of Senega and Onosmodium, and their usefulness in affections of the ocular muscles, and reported a number of cases in which these drugs had been used with apparent benefit.
The value of Senega in hyperphoria has been made the subject of a recent communication by Linnell, but as I have elsewhere endeavored to show, [Jour. O., O. and L., April. 1893.] the usefulness of the remedy in this disorder is by no means proven by the cases related. Indeed, the provings of Senega do not show any special adaptability of the drug to hyperphoria, so far as we understand the symptoms of this affection. Nevertheless, it might have an empirical or clinical value, but the evidence even here is defective. Norton says that the symptoms calling for Senega, are “dull, tired, aching, pressing pains in the eyes, or throughout the whole head, with smarting and burning in the eyes, always worse after using them and often accompanied by catarrhal symptoms of the conjunctiva.”.
Onosmodium has many symptoms of heterophoria in its proving, e.g., occipital headache; a dull aching pain extending down the back of the neck, or over one side of the head, generally the left; vertigo, with strained or stiff sensation in the eyes, aggravated by use of the eyes for near work. Gelsemium has a transient vertical diplopia, and may be of value in those cases of hyperphoria accompanied with the paretic or other characteristic symptoms of the remedy. Stramonium shows a marked vertical diplopia in its provings. The importance of this symptom in the proving of a drug, is simply that it indicates that the drug has a direct influence upon these muscles which are concerned in the production of hyperphoria.
We do not find diplopia (unless it be transitory) in heterophoria. But as a drug-symptom, diplopia is an indication that the remedy has an action along the line in which we seek for curative effects, and suggests that it may possess valuable therapeutic properties in the treatment of affections of the upward and downward turning muscles of the eyes.
So far as the applicability of these or other drugs to the cure of hyperphoria, is concerned, the evidence in their favor, is at the best, obscured by the fact that in almost all of the cases reported, other treatment than the medicinal was given the patient, so that the action of the remedy is not clearly shown. Norton, himself, limits all attempts at a cure by remedies to hyperphoria of less than 2 degree. In higher degrees, an immediate tenotomy was advised.
Systematic exercise of the affected muscles by means prisms, has been used and recommended as a cure for hyperphoria, and the clinical evidence in our hands is favorable to its usefulness. In hyperphoria of 1 degree and perhaps 2 degree, if persisted in, it may effect a cure, but in higher degrees it does not seem to be of much value.
In a case where there is a manifest hyperphoria of say 1 degree, circumstance often suggest that there is an additional amount that is latent, and a correcting prism is prescribed, to be worn constantly, for the purpose of revealing this latent defect. Under these circumstance, in many instances, the daily examination will show an apparent increase in the hyperphoria, until we may have developed in the course of a week, beginning with 1 degree, as much as 5 degree or more. This final amount is then accepted as the total of the real hyperphoria present, and made the basis of an operative correction.