CHAPTER XVIII AMBLYOPIA, AFFECTIONS OF THE CoLOR SENSE, AND (Part 1)

CHAPTER XVIII AMBLYOPIA, AFFECTIONS OF THE CoLOR SENSE, AND DEFECTS OF THE VISUAL FIELD The literal meaning of the word amblyopia is subnormal vision without any apparent fault in the eye, but the term commonly is applied also to many other conditions in which the sight is im- paired either by congenital faults, or by lesions which are now known, but were not formerly recognized to be characteristic of disease, or of poisoning, even when gross changes are present in the fundus. The vision may be normal for black and white and yet subnor- mal for colors, so amblyopia may be said to range in degree from a slight reduction of the vision below the accepted standard, or a slight defect of the color sense, to total blindness. Amaurosis means literally total blindness without obvious cause, so it may be understood to be the extreme limit of amblyopia, though the word often is used synonymously with blindness from any cause. Am- blyopia may be either congenital or acquired; in the latter case it is due in most cases to disease, traumatism, or poisoning, and if we look carefully we shall find in many some indications of trouble in the fundus, or possibly that the amblyopia is confined to a central area of the field, when the patient has what will be described pres- ently as a central scotoma. Whenever objective signs are absent, so that the eye looks perfectly well, we must exclude malingering, especially when the patient is an adult, as we do not always know in what way benefit may accrue from a diagnosis of amblyopia to a person who claims to have faulty vision in one or both eyes, but we must never pronounce him to be a malingerer until we have proved him to be such. Ordinarily when we speak of amblyopia or amaurosis we refer to a lack of perception throughout the entire field of vision, but in many other cases we find areas of total, or of partial blindness in various parts of the field, which may or may not be perceptible to the patient, but can be detected, measured, and delimited by means of the perimeter. These are spoken of generally as defects in the 408 AMBLYOPIA 409 field of vision. When the blindness is total in the affected area the defect is said to be absolute, when the light sense is preserved it is called relative. A relative defect may be for color alone. An island of absolute or relative blindness in the field is called a sco- toma. A triangular area with the papilla at its apex is a sectorlike defect. Absolute or relative blindness of one half of the field is hemianopsia. AMBLYOPIA CONGENITAL AMBLYOPIA We seldom if ever find the visual power of the two eyes to be exactly the same in any person after all of the refractive errors have been corrected, and it is well known that the visual acuteness varies considerably in different people, but we consider such variations to be physiological and in no way indicative of amblyopia as long as the vision is equal to or better than the standard which has been accepted commonly as normal. It is only when the vision of an eye has been found to be subnormal after all of the refractive errors have been corrected, and we are convinced that the condition has existed since early childhood, that we make a diagnosis of congenital amblyopia. In many cases only one eye is affected, and this is, or has been strabismic; then we may debate whether the amblyopia was con- genital, or has resulted from disuse, without much hope of arriving at a conclusion. Sometimes the amblyopia may have been caused by injury to the retina by hemorrhages at the time of birth, but such cases seldom can be differentiated. Defects of structure account for some, and when these are bilateral the patient is apt to have nystag- mus. <A considerable degree of hypermetropia, or of compound hypermetropic astigmatism, may render one or both eyes ambly- opic. When this trouble is bilateral we can often obtain a great improvement in a few months through the constant wearing of glasses that correct the refractive errors, but though we may occa- sionally secure a similar improvement when only one eye is affected, through making it work after its refractive errors have been cor- rected, we are not often able to do so, and when we cannot it is hard to determine whether the amblyopia is due to this, or to some other congenital cause. If the patient never had strabismus, has no great 410 DIAGNOSIS FROM OCULAR SYMPTOMS refractive error, and particularly if he has binocular single vision, we must exclude all forms of acquired amblyopia, as well as malin- gering, before we can accept it to be congenital. ACQUIRED AMBLYOPIA When the sight of an eye is known to have been good, and then to have been impaired or lost, either suddenly or gradually, we are able in most cases to find some lesion in it to which we can attribute the loss, but occasionally we cannot, and then we say that the patient has acquired an amblyopia, the cause of which we then try to ascertain. Sometimes we can detect some slight changes in the fundus that do not seem to us to be competent to explain the deterioration of the vision, but the only cases in which the lesions in the fundus are gross and prominent to which this term is applied are those that have had the symptoms produced by the toxic action of drugs, and these are all included under the name toxic amblyopia. Acquired amblyopia is met with occasionally in only one eye, but as a rule it is bilateral. Traumatic Amblyopia ‘When a patient complains of amblyopia or amaurosis as the re- sult of a traumatism to the head or spine, but presents no lesion in the fundus or elsewhere in the eye, we must search not only for symptoms of an intracranial lesion that might affect the centers of the optic nerve, but also for signs of any general disease which might produce a similar condition, look for stigmata of hysteria, and exclude malingering. The last is met with most often in connection with court cases in which the plaintiff desires to secure unduly high damages, but is to be excluded painstakingly in all cases, as we can- not tell what harm may result from a failure to unmask an impostor. When all of these things have been excluded we are justified in pro- nouncing the condition of the patient to be a traumatic neurosis. Amblyopia from Bright Light When a person has been exposed for a considerable time to the reflection of the sun’s rays from the surface of snow or water, or has been close to an electric flash caused by a short circuit, or has AMBLYOPIA All been exposed to such a bright light as that produced in electric welding, he may have a distinct impairment of his vision either with or without any discoverable lesion in the fundus. As a rule the amblyopia is temporary, but in bad cases it may be permanent, or blindness may be produced. Gazing at the sun, usually at the time of an eclipse, likewise is able to induce an amblyopia, which some- times is attended by a central retinitis. Ordinarily we find a rela- tive central scotoma for color in these cases, though sometimes the scotoma is absolute, and we may find the color vision defective else- where in the field, while some patients complain of metamorphopsia. Swanzy says that when the cases are not severe improvement takes place in the vision, but complete recovery is not common, and that no case in which the vision was reduced below 6/18 has been known to regain 6/6. Amblyopia from Disease In the absence of any history of poisoning, traumatism, or ex- posure to a bright light an acquired amblyopia is an indication that should lead us to a thorough investigation of the organism for all diseases that may induce trouble in the retina, or in the optic nerve. A careful inspection of the fundus may reveal very slight changes that escaped our notice at first, such as a slight haze that directs attention toward syphilis or nephritis, a hyperemia that suggests malaria, or an uncertain pallor of the temporal sector of the papilla. If we think that possibly we have seen the last we test the central vision for a scotoma for red, which may be the first symptom of a diabetes, or a symptom of multiple sclerosis, but always suggests much more strongly poisoning with alcohol and tobacco. If the patient is very ill he may be suffermg from ptomaine poisoning, also called botulism, or he may be in a state of exhaustion from some grave disease, either of which is a sufficient explanation, or he may have had a large spontaneous hemorrhage, which for some un- known reason is more apt to induce amblyopia than an equal loss of blood from a wound. Reflex Amblyopia Cases have been reported in which the cause of an amblyopia has been proved to be reflex by its disappearance as soon as an appar- ently unrelated source of irritation was removed. Carious teeth were at fault in the majority of the cases, but troubles in the nose, 412 DIAGNOSIS FROM OCULAR SYMPTOMS intestines, genitourinary organs, and perhaps elsewhere, have been quoted as the causes. The diagnosis can be made only after relief has been obtained, but the possibility of a reflex cause should be borne in mind whenever we have to deal with a case of acquired amblyopia that seems to be inexplicable, and a search should be made for a source of irritation. Hysterical Amblyopia When a patient complains of blindness of one eye, while the media and fundus are perfectly normal, we suspect hysteria at once. Less often the complaint is of imperfect vision of one eye, but it is only in rare cases that both eyes are affected. The patient usually is a neurotic woman, but may be either a man or a woman of good physique whose appearance does not cause us to think of hysteria. In every case we have to rely upon the finding of concomitant, inexplicable nervous symptoms for our diagnosis. We must be watchful to see that the symptoms we elicit are not those of some organic lesion of the central nervous system, as it 1s quite possible for an amblyopia associated with anomalous nervous symptoms to be the first sign of such a lesion, and it is only when the symptoms found are irreconcilable with any organic trouble that a diagnosis of hysterical amblyopia is justified. If a ptosis, or a blepharospasm, appeared coincidently with the amblyopia; if both eyes are in a state of conjugate deviation; if the pupil is dilated, whether it responds to light or not; if the patient suffers at the same time from asthenopia, or from diplopia; or if objects are said to appear to be larger or smaller than they should, we first search for a cause to explain these accompanying symptoms, and if none can be found we feel confident: that the trouble is hysterical. When sufficient vision is present to enable us to use the perim- eter we have no doubt as to the diagnosis if we find an irregular concentric contraction of the field for white, which changes rapidly in shape and extent, as shown by the results of several examina- tions made in succession, and particularly if we find that the fields for color exhibit gross anomalies, such as an overlapping of their margins, or a reversal. The field for red has been found to be larger than that for white in some of these cases and a relative scotoma is common. When the eye is amaurotic we test the other senses, and if we are AMBLYOPIA 413 able to find anomalous areas of anesthesia to touch, pain, or tem- perature somewhere on the body, a loss of certain reflexes, or anomalies of taste, smell, or hearing, that cannot be referred to a lesion in any part of the central nervous system, we are justified in a diagnosis of hysterical amaurosis. There seems to be a central disconnection between the conduction apparatus of the eye and the percipient function of the brain in these cases, for sometimes we can prove that the amaurotic eye does see by placing a five or six degree prism in front of it, when the patient sees two lights as though the sight in both eyes was normal, yet the patient is not a malingerer, the loss of vision is just as real to her as though the eye was really impaired. Toxic Amblyopia A bilateral acquired amblyopia leads us to question the patient quite closely with regard to his occupation and habits, as well as concerning any recent or long past overdose with any drug, in order to try to obtain a clue to the cause. The occupation may lead us to suspect chronic poisoning with lead, bisulphide of carbon, or aniline oil, the habits may reveal a chronic poisoning with alcohol and tobacco, while many drugs are able to impair the vision when an overdose has been ingested. Lesions in the fundus are produced in the great majority of cases, though they are not always typical. Lead induces a great variety, that range from no visible changes to a high degree of neuroretinitis with hemorrhages, and we make the diagnosis in such a case from the occupation and the presence of other symptoms of lead poisoning. If we find a pallor of the temporal side of the papilla, with a contraction of the periphery of the field and a central scotoma for red in a patient whose occupa- tion exposes him to the danger of poisoning with bisulphide of carbon, we ascribe his toxic amblyopia to this cause. The occupa- tion together with a violet color of the fundus and dark vessels leads us to ascribe an amblyopia to poisoning with aniline oil. Disease of the papillomacular bundle of nerve fibers means chronic poison- ing with alcohol and tobacco in most cases, but it may be caused by poisoning with lead, bisulphide of carbon, iodoform, or cannabis indica, as well as by certain general diseases. A retinal ischemia with very small vessels suggests that a toxic dose of quinine has been taken, while a retinal hyperemia may indicate a toxic dose of phosphorus, scammony, colocynth, or pomegranate. 414 DIAGNOSIS FROM OCULAR SYMPTOMS Toxic Amblyopia from Quinine A sudden attack of blindness, deafness, and tinnitus aurium, with both retine of a grayish or yellowish white color, and both disks very pale with extremely small blood vessels, forms such a char- acteristic clinical picture that we have good reason to fear when we see it that the patient has taken an overdose of quinine. In the majority of cases we have no difficulty in making the diagnosis, as we are informed at once that the patient has taken an enormous dose of the drug. Patients differ greatly in their susceptibility to quinine. Some can take doses that may be called truly heroic with- out apparent harm, while others exhibit toxic symptoms after the ingestion of as small an amount as two grains, and a temporary blindness has been produced by fifteen grains given in divided doses in the course of twenty-four hours. When sufficient vision is pre- served to enable us to map out the field we find it much contracted. The prognosis is commonly thought to be good, but this is ques- tionable. As a rule the vision returns after the drug has been eliminated, the blood vessels refill, and the fundus regains its normal color, but the field is apt to remain contracted. Exceptional cases have been reported in which the patients remained blind for life, but this is unusual. In spite of this return of good vision it has been observed repeatedly that the vision is apt to deteriorate slowly, and that at the end of many years the papilla may be found to be pale, the blood vessels small, and the vision to be quite poor. From the researches of Holden, and of de Schweinitz, it would appear as though the effect of the drug is exerted primarily upon the ganglion cells of the retina, and that it also produces inflammatory effects in the walls of the blood vessels. ‘These effects may perhaps be sufficient to explain such a slowly progressive atrophy without re- course to the idea of a persistent toxic action of the drug upon the nerve fibers, but we cannot say that the prognosis is good when such an impairment of the eye is at all likely to be the final result. If the patient denies having taken quinine he may have taken instead a toxic dose of salicylic acid, oil of wintergreen, ergot, some of the coal tar products, filix mas, potassium chlorate, cocaine, adrenaline, nitrobenzene, or dinitrobenzene, all of which are said to be able to induce similar pictures, though they vary somewhat in their details, and usually do not have features that are quite so pronounced. AMBLYOPIA 415 Toxic Amblyopia from Alcohol and Tobacco When a middle-aged or elderly patient complains of a gradual deterioration of vision for both distance and near, which cannot be corrected by glasses, and we find a central scotoma for red due to a disease of the papillomacular bundle of optic nerve fibers, the proba- bility, if the patient is a man, is that he has been using both alcohol and tobacco to excess for many years. Usually this fact is admitted at once, and then, after we have excluded the other possible causes of disease of this bundle, the diagnosis is made. Occasionally a patient is untruthful about his habits in that he will deny drinking