CHAPTER XIX HeEapACcHE, NEURALGIA, AND EYESTRAIN (Part 3)

advances it becomes more and more difficult for this muscle to overcome the hypermetropia, and when finally the vision has become subnormal we know that there was a time when perfect distant vision was main- tained only by the full force of the normal tone, yet many patients who have difficulty in seeing objects distinctly either in the distance or near at hand, tell us of the fine sight they formerly possessed and of its loss, but make no mention of any symptoms that we can refer to eyestrain which appeared at, or a little before the time when their vision began to fail, while other patients in the same condition do tell us of a past possible eyestrain at about that time, when we can find no evidence of muscular weakness, or of spasm. Such a history is inconclusive because the symptoms might have been caused by, some trouble elsewhere, which was in no way connected with the eyes. We know that a ciliary muscle, which has proved itself fully com- petent to correct the hypermetropia during good health, is apt to be- come unable to do so when all of the muscles of the body have been weakened, and we often see symptoms of eyestrain appear when the eyes are taxed during convalescence from sickness, to pass away as the muscular system regains its normal tone. When we measure carefully the manifest hypermetropia of a young adult who is suffer- ing from eyestrain by slowly increasing the strength of the convex glasses by which it is corrected, it frequently happens that we find — the manifest to be nearly or quite equal to the total as determined under atropine, instead of maintaining about its normal ratio to the latent, and then almost invariably we find the tone of all of the muscles in the body to be below par. If the symptoms are relieved in such a case by convex lenses that correct the hypermetropia it seems to me that the diagnosis should be eyestrain due to abnormal weakness of the accommodation dependent on some cause outside of the eye which affects the musculature of the entire body, though ordinarily we speak of it as caused by the hypermetropia. We meet with exactly the opposite condition in many cases in which the constant demand made upon the ciliary muscle has induced HEADACHE, NEURALGIA, AND EYESTRAIN 451 a contraction that exceeds its normal tone. We call this spasm of the accommodation and find it to be a common cause of eyestrain. These cases form the great bulk of those in which the use of a cy- cloplegic is admittedly necessary. Sometimes we can secure a cer- tain amount of relaxation by allowing the patients to look for a while through the convex lenses that correct the manifest and gradu- ally increasing the strength of the glasses as the manifest increases, and, if we have perfect control over our own accommodation, we may be able to measure the total with the ophthalmoscope and so learn what proportion is latent. When we can do this we are apt to find that the latent seems to be greater than it should be in proportion to the manifest, when we take into account the age of the patient and the muscular tone of the body, or we may find an apparently myopic eye to be hypermetropic, but we have no reliable rule to guide us concerning the ratio of the manifest to the latent hypermetropia, and we are unable to be positive that we have unearthed all of the latent until we have used a cycloplegic. Less often we meet with cases in which the spasm of the accommodation is so strong and persistent that we can make out little if any variation from the manifest hyper- metropia or myopia without a cycloplegic, and my experience is . that the weaker cycloplegics are of little value in this condition. An example which is illustrative of quite a number is that of a young lady who had consulted several excellent ophthalmologists in search of relief from eyestrain, and had been adjudged by all of them to have not over a diopter of hypermetropia. ‘The ophthalmoscope revealed no more, but atropine, which none of them had employed, disclosed four diopters in each eye, and subsequently I was told that the relief was complete. While the eye is under the influence of such a drug we have no means of determining the normal ratio of the manifest to the latent hypermetropia in that particular case, as an estimate made from the age and the general muscular tone is open to serious sources of error, so we have to wait until its effects have passed off before we can determine the true manifest. When the correction of this relieves the symptoms permanently we are certainly justified in saying that the eyestrain was due to the hypermetropia. A complete relief to the symptoms while the eyes are under the influence of a cycloplegic leads us to feel pretty confident that we shall find the cause to be either hypermetropia or astigmatism, but it is not a sure sign. The eyestrain from muscular imbalance may be 452 DIAGNOSIS FROM OCULAR SYMPTOMS noticeable only when the patient is engaged in near work, and the symptoms of nasal asthenopia are apt to be brought into prominence by the position of the head during near work, a position which is not likely to be taken while the eyes are incapacitated through paralysis of their ciliary muscles. Symptoms of eyestrain due to this cause almost invariably require the full correction of the manifest hypermetropia for their relief, but occasionally we meet with a surprise. A gentleman who com- plained of eyestrain had been fitted elsewhere with glasses that seemed to be perfectly correct. He could read 20/15 through them with each eye, and no better vision could be obtained for distance, yet his symptoms were relieved completely by a reduction of half a diopter in the strength of each lens. A lady who had been wearing simple cylindricals without benefit to her eyestrain accepted for her best distant vision -++- 1D spherical combined with + .50 cylindrical axis 90° over each eye, but secured relief only after the strength of the spherical correction had been reduced one half. Another curious case in this connection was that of a lady 46 years old who enjoyed perfect ease as long as she wore her correction for hypermetropia, except for the fact that she had to hold a book, or any near work, unpleasantly far from her eyes, but suffered from intense headache as the result of every attempt to correct her presbyopia. Myopia The great majority of cases of eyestrain met with in myopia will be found to be due .to some other trouble, for it is doubtful if this refractive condition ever excites such symptoms, at least unless it is associated with astigmatism, and even then the symptoms are apt to be slight. Probably this is because no strong muscular effort is ever habitually required within the eye. When eyestrain is asso- ciated with an apparent myopia we should make sure that the latter has not been simulated by a powerful spasm of the accommodation, and the most certain way to do this is to instill a solution of atropine into the conjunctival sac. The spasm yields within a few days in the majority of cases, and then we almost always find the refraction to be hypermetropic. In exceptional cases the spasm is of some other origin, and I have grown to suspect this to be the case when it is unusually resistant to the effects of this drug. In one youth who apparently had about two diopters of myopia with some hyperexo- HEADACHE, NEURALGIA, AND EYESTRAIN 453 phoria the ophthalmoscope revealed emmetropia, but the spasm did not yield until after the atropine had been used for some two months. In another youth who had apparently about the same degree of myopia with both the test lenses and the ophthalmoscope the severe symptoms of eyestrain led me to instill atropine for several weeks with no avail, and then to perform a partial tenotomy on his superior rectus in the hope of relieving the symptoms through a correction of from 2/8 to 3/4 of a degree of hyperphoria. To my surprise he read 20/20 with his naked eyes after the operation, and the refrac- tion appeared to be emmetropic, although no change in the muscular condition could be detected two weeks later. In both of these cases the eyestrain seemed to depend on the spasm of the ciliary muscles in eyes that were at any rate not very hypermetropic. Whether it was caused in either or in both bv the muscular imbalance is an open question. We must not be misled by the fact that a spasm of the accommo- dation can simulate myopia in rather rare cases into thinking such a spasm to be present because we find the myopia to be slightly less when the eye is under the influence of a cycloplegic than when it is not. This is particularly true if the patient does not complain definitely of eyestrain. Such a variation is physiological, and is the measure of the tone of the ciliary muscle. Unless contraindicated by some other consideration the full amount of the myopia should be corrected, because the myopic eye tends to keep its health better when its ciliary muscle is called upon to perform its normal amount of work, and the patient then enjoys his best vision. Astigmatism Many cases of eyestrain are due to slight degrees of astigmatism, which may be either simple or compound, but almost invariably is hypermetropic. We obtain a fair estimate of the amount and the axis of the astigmatism from the curvature of the anterior surface of the cornea as shown by the ophthalmometer, and by means of reti- noscopy when the eye is under the influence of a cycloplegic, but neither of these methods is infallible, both must be controlled by our findings with the test lenses and by the subjective sensations of the patient. Often when we place the lenses that correct the astigmatism before the eyes of the patient and have him take his attention away from the test card, we are gratified by the remark that the glasses 454 DIAGNOSIS FROM OCULAR SYMPTOMS have relieved the headache completely, and then the diagnosis of eye- strain from astigmatism is made. Not so very infrequently we at- tain this result with cylindrical lenses that do not correspond exactly with our findings by any objective method, but are a little weaker or stronger, or have their axes a little different from what these find- ings would lead us to expect, and when we find this to be the case we know that we are dealing with an uncommonly intolerant eye, for most eyes accept an approximate correction readily, as has been men- tioned already. After we have ascertained by our tests what we believe to be the correction of the refractive error we can allow the patient to wear the correction for a few minutes and note the effect produced on the symptoms. If the relief is marked, or if the patient is conscious of a steady, gradual improvement, we feel confident that we have made the diagnosis; if little or no relief is felt we modify the glasses slightly both in strength and position and give full oppor- tunity for each change to produce relief if it can, but when none can be secured in this way it is well to investigate for other possible causes. In my experience, a correction of a refractive error which produces no effect on the symptoms of eyestrain at once is not very likely to succeed later, even though it may occasionally. Another fact worth bearing in mind is that sometimes when the patient has a low degree of compound hypermetropic astigmatism and is not relieved perfectly by the full correction, it may happen that a brilliant re- sult can be obtained by eliminating the spherical portion of the cor- rection, when we are justified in the conclusion that the eyestrain depends on the astigmatism alone. EYESTRAIN DUE TO HETEROPHORIA Very little has been written on the differentiation of heterophoria as the cause of eyestrain. Most writers seem to assume that the demonstration of a muscular imbalance is equivalent to the diagnosis, yet this can easily be proved not to be the case. We meet with all of the various forms of heterophoria in persons who show no signs of eyestrain, as well as in others in whom the symptoms can be traced to other sources, so that in any individual case the demonstration of an exophoria, an esophoria, a hyperphoria, or a cyclophoria, is that of a possible, but not necessarily of the actual cause, just the same as that of a refractive error, or of existing pressure within the nose. Heterophoria may be one of the symptoms induced by a mental or HEADACHE, NEURALGIA, AND EYESTRAIN 455 physical factor that disorders the nervous equilibrium, and then is symptomatic of, rather than a cause of the trouble. Not infre- quently it passes away, or at least fails to make its presence felt, when glasses that correct a refractive error are worn constantly. It sometimes appears in the course of diseases of the central nervous system, and I have seen several cases in which eyestrain with hetero- phoria seemed in the light of subsequent developments to have been symptomatic of derangements or diseases in the gastrointestinal tract, or in the genitourinary organs. This question of differentia- tion seems to me to deserve more attention than it has yet received, for there is no doubt that in an uncertain percentage of the cases heterophoria is the direct cause of eyestrain, and that some forms are more prone to excite these symptoms than are others. It is rather in the hope of stimulating investigation along this line, than of pre- senting anything final that the following points are propounded as of possible diagnostic value. When the patient has found that he is able to relieve his symp- toms of eyestrain and to continue his work in comfort by closing one eye, the source of the symptoms is located almost certainly in his eyes, and the chances are that it will be found in an imbalance of the muscles, though occasionally we will find it in a refractive error. To be the cause of eyestrain a heterophoria must be an anatomical entity and not an induced anomaly. We can induce heterophoria artificially by exercises of the muscles with prisms, by wearing pris- matic glasses, and by repeated tests of the muscles. About twenty years ago, while engaged in the study of the effects of prisms on my own eyes, I developed a hyperphoria that compelled me to wear a five degree prism base down over my right eye for a year and a half, which demonstrated how an artificial heterophoria could be produced. Another example was furnished by the patient alluded to who could disclose at will fifteen degrees of either exophoria or esophoria, but had orthophoria by the cover test. A heterophoria which has been induced in such a manner as this may appear to be real, so we should inquire into the possibility of an artificial production before we make our diagnosis. It does not seem to comport with common sense that a heterophoria which has been induced artificially should be con- sidered the cause of antecedent symptoms. The findings by all tests should show about the same degree of the same variety of heterophoria, and should they not agree the discrepancy should be explained before we assume that it is caused 456 DIAGNOSIS FROM OCULAR SYMPTOMS by an anatomical fault. At the time I was obliged to wear a five degree prism base down, to relieve the annoyance produced by an artificial hyperphoria, my eyes were examined with the tropometer, which showed their rotations up and down to be perfect, while the rotation of one eye inward was imperfect; the perfect rotations up and down seemed to promise recovery from the hyperphoria, which took place later, and the imperfect rotation inward coincided with the findings by no other test. The findings should not fluctuate greatly after short intervals of time. Marked fluctuations hardly seem to be consistent with a fixed error that is responsible for symptoms, and my attention has been attracted by such vacillations in several cases in which the hetero- phoria seemed to be symptomatic of an instability of the nervous system induced by over work, or by trouble in the abdominal organs. In quite a number it has seemed to be a question whether the symp- toms of eyestrain with heterophoria did not form the first indication of kidney disease that was observed, while in others these symptoms developed after the presence of the disease had been recognized, but in all of them the fluctuations in the degree of the heterophoria were considerable, and to me at least were puzzling. This may be explained as simply a coincidence in the small number of cases that were observed, but when fluctuations are present it can do no harm to investigate the other organs of the body before we decide that the heterophoria is the cause of the eyestrain. The prism convergence, the prism divergence, or the sursumver- gence of the eyes should show a fault if the imbalance of the mus- cles is very marked. ‘This is not necessarily so when the hetero- phoria is slight. We may consider these tests to be corroborative when the adduction is less than normal while the abduction is of full strength or excessive in a case of marked exophoria, or when the reverse is true in one of a high degree of esophoria. The sursum- duction of the two eyes should be alike,