CHAPTER XVIII AMBLYOPIA, AFFECTIONS OF THE CoLOR SENSE, AND (Part 4)

have been taken from de Schweinitz:— Blue Red Green QOutwarde,...° Rie Se ee 80° 65° 50° Outward and upward ......... 60° 45° 40° Wpward> ss sceeene 40° 33° 20 Upward and inward ......... 45° 30° 25° Inward 4.40 ole aeeee 45° 30° 25° Inward and downward ........ 50° 85° Oi Downward: irre 58° 45° 80° Downward and outward ...... fie 55° 45° We can easily construct a chart for our guidance by tracing the outlines of the various fields according to the above figures on any of those to be obtained in the market, and this will be more useful if the tracing is made with inks that correspond to the colors indi- cated, using black to delimit the field for white. CONTRACTION OF THE FIELD OF VISION When the limit of the field is materially less in any direction than is indicated on such a chart, and this variation is not to be explained by some unusual prominence of the tissues about the eye, the field is said to be contracted. If this contraction affects only one part of DEFECTS IN THE FIELD OF VISION 429 the periphery we look for some local affection of the retina, such as a detachment, unless it happens to be of the nasal portion, when our first thought is of glaucoma. When the boundaries are constricted in all directions we have concentric contraction, which is met with in all of the affections that impair the general efficiency of the optic nerve and retina, is well marked in optic atrophy, and may be said to be the commonest functional disturbance of the eye. Its degree is found to vary from one that is not noticed by the patient and can be detected only by perimetric measurements, to one in which the patient is deprived of peripheral vision and seems to see through a tube. Such an extreme concentric contraction as the last with more or less good central vision is quite suggestive of pigmentary de- generation of the retina, but it is met with also in traumatic neuroses and in hysteria. A distinctive feature in these cases is that when such a tubelike contraction of the field is produced by retinal disease the orientation is impaired so badly that the patients are scarcely able to go about alone, while there seems to be little if any such difficulty when the contraction is caused by hysteria or the neuroses. A de- fect of this nature has been counterfeited sometimes, so a test for the detection of simulation has been given under malingering. A transient concentric contraction has been found sometimes after an attack of epilepsy. The frelds for color may be contracted in a similar manner, or they may be distorted, in that they are made to overlap or interlace, or they may be reversed. Distortions and reversals of these fields we usually find to be symptomatic of lesions in the central nervous system, of neuroses, or of hysteria. A curious phenomenon, which is met with in some cases of trau- matic neurosis and might be mistaken for a contraction, is Foerster’s displacement of the field. The distinctive feature of this is that the boundaries of the field are not the same when they are tested by the appearance, and by the disappearance of an object on the perimeter. For example, if we bring the test object into view from the temporal side the patient perceives it at 90°, and after we have carried it past the center he loses it say at 80° on the nasal side; then when we reverse the procedure and bring the object into view from the nasal side he perceives it at 60°, and loses it again at 60° on the temporal side. In such a case we could readily make a mistake and think the field contracted concentrically, if we tested it by moving the test object from the center outward, although no contraction really was 430 DIAGNOSIS FROM OCULAR SYMPTOMS present. It is always best to determine the boundaries of the field by moving the test object from without inward. SECTORSHAPED DEFECTS IN THE FIELD OF VISION Sectorshaped defects may be caused by lesions in the retina, or by affections of the central nervous system. When they cut the fields for white and for colors evenly they are apt to be caused by an occlusion of certain of the retinal vessels, or by the interruption of the conductivity of a group of nerve fibers in the retina. A triangu- lar defect with its apex at the papilla, at a point corresponding to the position of a circumscribed patch of retinochoroiditis close to its margin, may be held to be the diagnostic feature which marks the case as one of retinochoroiditis juxtapapillaris, and not one of an accidental location of a patch of choroiditis at this point. Other sectorlike defects are met with in tabes, and in multiple sclerosis, but in these the boundaries for white and for colors are not apt to coincide. Still other defects of this shape may be partial hemi- anopsias. SCOTOMATA An island of absolute or of relative blindness in the visual field is called a scotoma. If it includes the point of fixation it is central; if it lies near, but does not include the point of fixation, it is paracen- tral; if it lies at a considerable distance away from this point it is peripheral. Sometimes the island forms a more or less complete circle about an unaffected point of fixation, and then we call it an annular or a ring scotoma. A positive scotoma is one which brings itself to the notice of the patient, a negative scotoma is one of which he is unconscious. A positive paracentral or peripheral scotoma is most likely to be caused by an opacity in one of the refractive media, for the simple absence of vision in an island of the retina which does not include the fovea is not apt to be noticed subjectively, unless it is quite large, although there may be a certain amount of conscious- ness of its presence when the retinal pigment and the choroid are affected, but a central scotoma is sure to attract attention through the impairment of the central vision. Negative paracentral and peripheral scotomata usually can be referred to lesions in the retina or choroid, though occasionally they are met with in disease of the central nervous system. DEFECTS IN THE FIELD OF VISION 431 The Blind Spot A round, or elliptical, absolute, negative scotoma is present in the field of every eye, between twelve and eighteen degrees to the outer side of and about three degrees below the point of fixation, corre- sponding to the place of entrance of the optic nerve. This is known as Mariotte’s blind spot. Its presence proves that the fibers of the optic nerve cannot be stimulated by light until after they have en- tered the retina. We find it enlarged, and perhaps misshapen, when medullated nerve fibers, conus, or posterior staphyloma is present, as well as in choked disk, in well marked neuroretinitis, and in glaucoma, but the principal diagnostic value of an enlargement of the blind spot is found in the cases in which it is symptomatic of a purulent inflammation of the posterior accessory sinuses. Central Scotoma When an object is seen better if it is a little to one side of the point of fixation the patient has a central scotoma. This may be relative, perhaps for red and green only, or it may be absolute, and it may be present in one eye or in both. If the patient states that objects appear to be distorted, or to be smaller than they really are, we shall probably find a central retinitis, a central choroiditis, or possibly a hemorrhage in the fovea centralis. A large, absolute cen- tral scotoma in one eye may be caused by a hole in the macula. Most cases of central scotoma are caused by disease of the papillomacular bundle of fibers of the optic nerve, and then usually, though not in- variably, they are bilateral. As a general rule we may say that a central scotoma of one eye alone is due to a local lesion at the fovea, while one that is present in both eyes is indicative of disease of the papillomacular bundle, but this is a rule to which there are quite a number of exceptions. An opacity in any of the refractive media that happens to lie in the visual axis of the eye produces a central scotoma, and this may be present in either one or both of the eyes. Ring Scotoma We do not know much about ring scotomata, and the use to which they can be put in making a diagnosis, further than that most cases occur in connection with pigmentary degeneration of the retina, that 432 DIAGNOSIS FROM OCULAR SYMPTOMS they are met with sometimes in choroiditis due to hereditary syphilis, as well as in diseases of the posterior ciliary vessels, and that they have been found in cases of diabetes, and perhaps in other diseases. Scintillating Scotoma When a patient describes the appearance of a positive central or paracentral scotoma in each eye, in the form of either a dark spot or a bright light, which enlarges until it has covered symmetrical portions of the two fields, while flickering bright points, or zigzag lines flash about in these areas, and these scotomata last from fifteen to thirty minutes before they recede, we say he has a scintillating scotoma. As a rule, these attacks are accompanied by vertigo, and are followed by pain in one side of the head, nausea, and perhaps vomiting, the usual symptoms of migraine, a disease to which this is so closely related that sometimes is is called ophthalmic migraine. Another name by which it is known is partial fugacious amaurosis. Sometimes the scotoma is not absolute, but forms a scintillating cloud before the eyes. It is said to have occurred in one eye alone, but such a case is uncommon. The scotoma usually takes the form of a homonymous hemianop- sia, but Swanzy states that “this defect may exist as symmetrical scotomata, complete or partial homonymous hemianopsia, or even horizontal hemianopsia. In some cases the scintillations may be ab- sent, while in others the attack of migraine does not follow.” He also says that it occurs most frequently in persons who are intellect- ually active, and that attacks have been known to be brought on by long continued reading, fatigue, and hunger. The etiology of this trouble is obscure. It is possible that the attacks are caused by an anemia of the occipital lobes which is brought about by some circulatory disturbance, the nature of which is unknown. As a rule it does not indicate the presence of any serious cerebral lesion, though possibly it may in cases in which it is of frequent occurrence, and is associated with other symptoms. HEMIANOPSIA Occasionally a patient tells us that when he is looking straight for- ward the right or the left side of the field is dark, or that everything above or below the horizontal plane is obscured, but more commonly we discover an obscuration of a half field during the examination DEFECTS IN THE FIELD OF VISION 433 of a patient who has symptoms of intracranial trouble. Such a phenomenon in only one eye suggests the presence of an intraocular lesion, such as a detachment of the retina, or a large hemorrhage, which interferes with the vision of one part of the retina, and we can imagine that such a lesion might occur symmetrically in both eyes so as to simulate bilateral hemianopsia rather closely. Glau- coma sometimes contracts the nasal part of the field quite decidedly, and when this disease is far advanced the rare binasal hemianopsia may be simulated to a certain degree, the more so as we sometimes find more or less of a concentric contraction of the preserved part of the field in hemianopsia, but the differentiation is easy because all lesions and diseases of the eye itself that can produce such a condi- tion are gross and detected readily. The distinctive features of hemianopsia are a more or less com- plete blindness of approximately one half of the visual field, de- limited by a fairly straight line, with no ocular lesion or disease that can account for it. This condition almost invariably is present in both eyes, very rarely occurs in one alone, and it indicates that the corresponding parts of the retine have lost their function. This loss on the part of the retine is called hemiopia. The defect is said to be complete when it involves the entire half of the field, to be incomplete when a portion of the affected half is not involved. It is absolute when there is no perception of light in the area, is rela- tive when light can be perceived but form and color cannot. The defect may be for color alone, when we call it hemiachromatopsia. Hemianopsia is divided into vertical and horizontal, in accord- ance with the direction of the line which separates the darkened from the preserved halves of the field. Vertical hemianopsia is sub- divided into bitemporal, in which both temporal halves of the fields are wanting; binasal, when both nasal halves are gone; and right or left homonymous, in which both right, or both left halves of the two fields are darkened. The homonymous is by far the most common form. The dividing line may be perfectly straight and pass through the point of fixation, but in most cases it makes a bend, or an angle, so as to pass around this point and leave it in the pre- served portion of the field. Several cases of double homonymous hemianopsia have been reported in which a small central field of vision was preserved in this way. The reason why this central point is spared in some cases and not in others is not yet known with cer- tainty, though theories have been advanced in explanation; it is 434 DIAGNOSIS FROM OCULAR SYMPTOMS probable that there are anastomosing nerve fibers about the macula, and possibly there is a separate center in the brain for this part of the retina. Hemianopsia always indicates a lesion in the brain that 1s so situated as to compromise the nuclei or fibers of the optic nerve, so when it is taken in connection with other symptoms it is of great value in localization. Bitemporal and binasal hemianopsia locate the lesion at the chiasm, as this is the only place where the fibers that pass to the temporal or nasal halves of the retine can be affected simultaneously. Horizontal hemianopsia, when present in both eyes, must be referred to an involvement of the upper or the lower fibers at the chiasm, to a lesion that affects both nerves simultaneously between the chiasm and the optic foramina, or to one that affects the upper or lower parts of both optic tracts in the same way. A lesion that presses from below or above on the optic nerve of one eye may cause a horizontal hemianopsia of that eye alone, and a double lesion in front of the chiasm may cause a loss of the upper half field of one eye, and one of the lower half field of the other. It would seem as though a similar encroachment upon an optic tract from below or above, back of the chiasm, would produce a homony- mous quadrant defect of the fields, which would probably be ac- companied by other symptoms indicative of disease at the base of the brain. A similar quadrant hemianopsia, that is not attended by motor or sensory symptoms, can reasonably be referred to a lesion confined to one part of the cuneus, while if it is attended by hemi- plegia and hemianesthesia the lesion is more likely to be beneath the cortex of the occipital lobe. Homonymous hemianopsia indi- cates that the conductivity of the nerve fibers which belong to one optic tract has been interrupted somewhere back of the chiasm, to and including the cuneus. Lesions along this lengthy stretch are likely to induce other symptoms, which vary in individual cases, and pertain not only to the eyes, but also to the mind, and to the sen- sory and motor functions of various parts of the body. By means of these symptoms we are able to locate the trouble first within a rather large area, and then by the relative predominance of certain ones we can sometimes determine its situation with a fair approach to accuracy. The majority of these lesions are tumors, which are apt to be attended by choked disk, but this symptom alone does not help us much. A right homonymous hemianopsia shows the lesion to be on the DEFECTS IN THE FIELD OF VISION 435 left side of the brain, and, conversely, the trouble is on the right side when the left half fields of vision are obscured. If the hemianopsia is attended by no motor, sensory, or mental symptoms we place the lesion in or about the cuneus. If the patient has no motor or sensory symptoms, but is unable to recognize, or to name correctly, objects when he sees them, although he is able to do both by means of his other senses, or if he has such psychie troubles as alexia, dyslexia, or color amnesia, we incline to locate the lesion outside of the cuneus in the optic radiations. As sensory disturbances appear we locate it farther and farther forward, until, when there is hemianesthesia of one side of the body, perhaps with ataxic movements, but with no distinct paralysis, we place it in the optic thalamus. The appear- ance of motor symptoms guides us still farther forward until, when the patient has both hemianesthesia and hemiplegia, we look for it in the posterior part