Under this heading are classed all those conditions where there is either partial or complete loss of vision without any perceptible ocular lesions. The term Amblyopia is applied to those cases where there is but partial loss of vision, and Amaurosis where the loss of vision is complete. Formerly many cases of loss of vision from excessive use of alcohol and tobacco were classed under the heading of amblyopia, but in the advance of ophthalmological knowledge they have been found to be cases of inflammation of the optic nerve behind the eyeball and are now classed as cases of retro-bulbar neuritis. Hemianopsia, while also considered under this heading, perhaps should not be, because, while there is no perceptible lesion of the eye, the cause is known as due to some cerebral disease.
Amblyopia ex Anopsia.-Weak-sightedness from disuse results when a child with hitherto healthy eyes commences to squint, for in an-effort to overcome the annoyance of seeing double he learns to suppress by a mental act the image seen by the squinting eye. As a result of this suppression when followed for months and years, there takes a permanent change in the nervous function of the eye, which is manifested by more or less loss of vision, amblyopia ex anopsia. This condition is often associated with high degree of hypermetropia and astigmatism and will usually not excite attention until the child has entered into school life, and is probably due to the fact that, owing to the refractive error, distinct images have never been focused upon the retina. If, however, the condition is not detected until adult life, no improvement is to be expected.
Other cases of amblyopia ex anopsia are due to non-use of the visual function, owing to congenital opacities of the cornea or lens, from persistent pupillary membrane, or in cases of strabisr in early infancy. There is usually but one eye affected in these cases, and, when the vision is defective in both eyes, nystagmus is often present. Often by bandaging the good eye and thus compelling the squinting eye to perform the function of vision, even for half an hour each day, the development of amblyopia may be prevented. An existing amblyopia can sometimes be benefited by this procedure; but as it has to be followed out for a very long time it is apt to be neglected. Naumow St. Petersburger Medicinische Wochenschrift, No. 3, 1889. in an analysis of 47 cases of death of new-born infants, has found in 12 cases retinal oedema, retinal haemorrhages into the macula, choroidal haemorrhages and the beginning of choked disc. The changes were found especially in those who suffered difficult and instrumental delivery, and he believes that congenital amblyopia has its origin in these changes, which are caused by stasis in the vessels of the head.
Traumatic Amblyopia may occur from any severe injury to the head, from concussion of the spine or from a direct blow upon the eye. In some of these cases there may be a fracture of the skull or a haemorrhage along some part of the nerve, which is apt to produce a neuritis; and, having then inflammatory signs in the eye, should not come under the classification of amblyopia. The prognosis of these cases, while often favorable, should, as a rule, be guarded and dependent somewhat upon the severity of the injury.
Amblyopia from Lightning.-Cases of loss of vision from a stroke of lightning are usually accompanied by such lesions as burning of the skin, hair or cornea; ptosis is often present and contract is apt to follow. In some cases there may be a neuroretinitis, or, later atrophy of the nerve. These cases often have a greater loss of vision than can be accounted for by the recognizable changes in the eye, and hence can only be considered in part an amblyopia.
Amblyopia from Loss of Blood.-Loss of sight may take place after severe haemorrhage and may be accompanied by changes in the retina or nerve, yet in some cases may present no visible lesions. It has been seen after severe haemorrhages from various organs, lungs, stomach, uterus, bladder, etc. Both eyes are usually affected in the large majority of cases and in nearly one-half the loss of sight is permanent. Temporary blindness may occur from loss of blood, and is due to the lack of blood supply to the visual centers or to the retina, and in these cases more or less complete recovery may be expected.
Hysterical Amblyopia.-Hysterical blindness is more frequently found in young girls and women. It is usually temporary and unaccompanied by hysterical symptoms. The loss of vision is usually complete, and but one eye is generally affected. These patients will often be made to see by placing a perfectly plane glass in the form of spectacles before the eyes and the result is due to suggestion. There is usually a concentric contraction of the field of vision, hemianopsia and color blindness may result from hysteria, and we have seen other functional disturbances, such as ptosis, blepharospasm and strabismus in hysterical subjects.
Pretended Amblyopia (Malingering).-The pretense of blindness is not infrequently met with, and, as a rule, these subjects only claim more or less complete blindness in one eye. Simulated blindness may be practiced for various reasons, the most frequent, perhaps, being in the order to secure damages after some trivial injury, to excite sympathy, to secure pensions, etc. We have seen blindness claimed from the mere lodgment of a cinder in the cornea, which had been removed, leaving no trace of its location behind.
An exaggeration, of an existing defect of the vision is often claimed. In all cases where the amaurosis is claimed to exist in both eyes, its detection becomes extremely difficult and may often only be proven by careful watching of the subject without his knowledge. The action of the pupils may give some clue; if dilated and immovable, the use of a mydriatic may be suspected, for in dilation of the pupil in true blindness there may be some contraction for the stimulus of a bright light or upon convergence and there is apt, also, to be a shade more of dilation when the eyes are in a shadow. By bringing an object suddenly before the eyes in assumed blindness there may be the natural closure of the lids to prevent injury to the eye. Where the loss of sight is claimed to be in but one eye, there are several tests that may expose the deception. The test by causing diplopia is perhaps the simplest. In this a prism of eight or ten degrees is placed before the sound eye with its base up or down, and if the person on looking at lighted candle fifteen or twenty feet away acknowledges the double images, binocular vision is at once proven. The crossed diplopia test is made by holding a prism of ten degrees base outward before the pretended blind eye, and if it really sees the eye will rotate inward for the sake of single vision. Another test is made by using a strong convex glass before one eye and a plane glass before the other to read the Snellen test type at twenty feet, and, by a reversible frame, make the person use unconsciously his bad eye. Again by paralyzing the accommodation of the good eye, or by placing concave lens in front of this eye, and, if the patient can read, we know it is done with the affected eye. The stereoscope, Snelling’s colored type and various other methods are also useful in discovering an assumed blindness of one eye.
In all these tests caution should be taken that the patient does not suspect that you are trying to detect his dissembling. Rather let him infer that you are seeking to find the cause of his amaurosis.
Hemeralopia (Nyctalopia, Night-blindness).-This condition is found quite frequently without any recognizable lesions of the eye and must be considered as distinct from the night- blindness occurring as a symptom of retinitis pigmentosa and other lesions of the fundus. Hemeralopia is a functional complaint due to exposure to strong, brilliant lights, and is more prone to affect those whose systems have become greatly debilitated from the want of proper food. It prevails sometimes as endemic in certain countries, as in Russia, during their protracted fasts; it is frequently found in sailor, from exposure to tropical suns, and is often by them called “moon-blindness;” in soldiers, after prolonged marches; in travellers in the arctic zone and in those who work before furnaces. Hemeralopia is sometimes congenital and then remains unchanged during life.
Persons suffering from night-blindness are found have good vision during daylight, but, upon the approach of dusk, or when going into a moderately darkened room, the vision becomes greatly impaired. The field of vision is normal and the fundus shows no lesion. THe cause of the difficulty is probably a torpor of the retina, and, under favorable conditions, improvement may be expected.
TREATMENT.-As the general health is usually more or less impaired in hemeralopia, a generous diet must be ordered. Rest and protection of the eyes from bright light are first required; in severe cases it may be necessary to confine the patient to a dark room with a gradual return to ordinary daylight.
Lycopodium is the remedy most commonly needed in this disorder. Many cases have yielded promptly to its use.
Other remedies, as China, Hyoscyamus and Ranunculus bulb, may be required.
Snow-blindness.__ The dazzling of the snow may produce a contraction of the visual field, scotoma and night-blindness from torpor of the retina. (See Retinitis nyctalopica.) In other cases it will cause intense photophobia, pain, blepharospasm and result in an acute conjunctivitis, or sometimes an ulceration of the cornea.
Color Blindness.__ Inability to discriminate colors is usually congenital, but may occur in diseases of the retina, optic nerve, brain or spinal cord, and consists of some impairment of the function of the retina. When not the result of disease, the subject’s vision may be in every other respect perfect. He will simply be unable to detect certain colors, as red, green or blue, when partial, and, when complete, all colors will be indistinguishable, simply black and white being recognized. Red is the color for which blindness is most frequently present, while the varying shades of green are next most frequently lost. Numerous theories have been advanced to explain the phenomena of color-blindness, of these the Young-Helmholtz and the Hering are the more generally accepted.
The Young-Helmholtz theory originally suggested by Thomas Young, in 1807, who considered that there were three sets of color-perceiving elements in the retina, corresponding to the fundamental colors, red, green and violet, and that all other colors are mixtures of these sensations. This assumption was modified by Helmholtz, who suggests that all colors excite the red, green, and violet elements at the same time but in varying degrees of intensity.
According to this theory red-blindness is due to absence or paralysis of the organs perceiving red, and that therefore the red-blind have but two fundamental colors__ green and violet.
The red colors then exciting only the organs for green and violet, and the latter but very slightly appear to the red- blind as a green of feeble intensity, white the light shades of red do not excite the organs for green, in the red- blind, sufficiently to even create the sensation of green but appear to them as black. The sensation of green excited by red rays in those who are red-blind is of a less degree of brilliance than the green colors appear to them, because red does not stimulate the fibres for the perception of green to the same extent as does green. In this way the red-blind is generally able to distinguish red from green, not by the difference in color but by the difference in brilliancy. By experience he learns to recognize reds from greens and may go through life without being aware of any defect.
As the man with red-blindness only distinguishes between red and green of equal brilliancy by the fact that the red appears darker, we can by decreasing the brilliancy of the green find a shade which will excite exactly the same sensation as does the red, and he is then unable to tell the two colors apart. Such colors are known as confusion colors and are used to detect color blindness.
In green-blindness the case is of course reversed, the elements perceiving green being either absent or paralyzed, the green blind having only the red elements excited by green it appears to them as red.
Hering’s theory is based upon an analysis of the sensation received when looking at a color. All colors excepting four primary colors-red, green, blue and yellow__ excite in us a mixed sensation. These primary colors form two pairs, red and green and yellow and blue, each color being antagonistic to its mate. They are also known complementary colors, because when mixed in proper proportions they neutralize each other and produce the sensation of white. These pure colors excite in us a simple, unmixed sensation, but other colors excite a mixed sensation, as, for example, orange gives an impression of both yellow and red. According to Hering’s theory, both white and colored light cause chemical changes in the retina or its visual substances, which he says are of three kinds, the white-black, the red-green, and the blue-yellow. He believes color-blindness to be due to the absence of one or both of the colored visual substances. In red-green blindness there is absence of the red-green visual substances and this variety is quite common. The blue-yellow blindness is very rarely found, if both the colored visual substances are absent there is total color blindness, this form extremely rare, and, in fact, its existence is denied by some.
To the red-green blind both red and green appear white or gray. This variety of color-blindness is found in about four per cent. of males, and in about one-fourth of one per cent. in females.
Color-blindness causes no trouble expecting to those in certain callings, as painters, railroad and nautical service, etc.
Heredity seems to play an important role in the occurrence of color-blindness.
There are upward of forty different tests that have been suggested for color-blindness, but the best is that made by Holmgren’s wools, which consists in having the observer select from a heap of wools of various shades those that correspond to the one given him as a test object. There are three test to be made. The first will detect all those who have any defect of color-vision, and the others show the nature of the defect.
In the first test, a skein of light pure green, rather freely mixed with white, is used and the patient required to select all the corresponding shades of green. If he selects any of the confusion colors, viz.: grays, drabs, yellows, rose and salmon, or hesitates and shows doubt as to whether he should choose one, then he should be subjected to the second test. For the second test a bright shade of purple (rose) is taken as a test; the confusion colors are blues, violets, grays and greens. If the patient be red-blind he will choose the blue and violet, because purple being composed of red and violet or blue, is to the red-blind identical with the two latter colors; while if he be green-blind, he will choose a gray and bright green. For the third test a bright red skein is selected, the confusion colors for this being the dark and light shades of green, and brown or olive. The red-blind chooses a green and dark brown; while the green-blind selects a green or lighter brown
In acquired color-blindness there is impairment of the visual acuity. There may be constriction of the field both for white and colors, or in some cases a normal peripheral field with a central color-scotoma. Acquired color-blindness is usually dependent upon some disturbance of the nerve- fibres, as in neuritic atrophy or toxic amblyopia. In neuritis the vision may be but slightly impaired and the field for white but slightly contracted, and still we may find color-disturbance, from a slight limitation for a single color to total color-blindness. In atrophy of the optic nerve, together with the decrease in the vision and concentric contraction of the field for white, we have failure of the color-sense first for red and green and last of all for blue. In toxic amblyopia, especially when due to alcohol and tobacco, there is in the either stages a relative scotoma for red and green. There may be peripheral defects for the same colors, and in rare cases a small central scotoma for blue. In toxic Amblyopia the relative scotoma, i.e., for colors, in the later stages as the disease progresses becomes an absolute scotoma, blind to light of any kind.
Hemianopsia (Hemiopia, Hemianopia).__ Obscuration of one half of visual field almost always involves both eyes. The division is almost universally vertical, although cases have been reported in which the upper or lower half of the field has been lost.
Vertical Hemianopsia may be of three varieties. The most frequent form is that of homonymous hemianopsia, in which the corresponding half of the field of each eye is wanting. Thus the right half of the field, from the patient’s point of view, is lost, and is due to a loss of function in the left half of each retina and is called right homonymous lateral hemianopsia, and is vice versa when the left half of the field of each eye is wanting.
Temporal hemianopsia (or heteronymous lateral hemianopsia) is where the external or temporal half of the field of each eye is blind. The form of hemianopsia is due to loss of conducting power in the nasal halves of the retina and results from pressure or disease at the angles of the commissure or the inner strands of the optic nerve just before reaching the chiasm. This form comes on less suddenly than the homonymous.
Nasal heteronymous hemianopsia is where both nasal fields are wanting and is the most rate form of vertical hemianopsia.
In the two last forms of heteronymous Hemianopsia the dividing line is apt to be irregular, while in homonymous cases th line of division is usually distinct and vertical.
Horizontal hemianopsia may occur in diseases of the eye or possibly from some lesion causing pressure upon the lower or upper part of the optic nerve or chiasm, or downward upon one optic tract.
Monocular hemianopsia may occur from a lesion of on optic nerve in front of the chiasm and, as a rule, has an irregular boundary line.
Hemiachromatopsia is where the color sense in corresponding halves of each eye becomes lost. This is an extremely rare condition and but very few uncomplicated cases are on record. The lesion is probably in the cortex.
In a defect of the light sense where there is a corresponding defect in the form and color sense it is called absolute Hemianopia. In cases where there is defect for form, with an equal defect for colors, the light sense remaining intact, it is called relative hemianopsia. Wilbrand Hemianopsia. Berlin. 1881. concludes that the centre for form lie between the centre for color and light sense and that the centre for colour occupies the most central position in the brain. When the hemianopsia is partial the defect is usually of an equal extent in both eyes. The reaction of the pupil in hemianopsia is always a valuable diagnostic sign, and th examination of the pupil should be made in a dark room, the eye illuminated with a weak light, while an intense light is thrown obliquely in various directions into the pupil. According to Wernicke, if, in hemianopsia, the light thus thrown upon both the seeing and blind sides of the retina causes contraction, the lesion is back of the primary optic centres. If there is contraction when the light falls upon the seeing side of the retina and none when it falls upon the blind side, the lesion is either in or in front of the primary optic centre. Peripheral contraction of the field that remains in hemianopia in
Diagram illustrating the visual path and its relation to the visual field, left lateral hemianopsia being shown (Seguin). L.T.F., left temporal half-field; R.N.F., right nasal half-field; O.S., oculus sin.; O.D., oculus sin.; O.D., oculus dexter; N.T., nasal and temporal halves if retinae. N.O.S., nervus opticus sin.; N.O.D., nervus opticus dext.; F.C.S., fasciculus cruciatus sin.; F.L.D., fasciculus lateralis dext.; C., chiasma, or decussation of fascicula cruciati; T. O. D., tractus opticus dext.; C. G. L., corpus geniculatum laterale; L. O., lobi optici (corpus quad.); P.O.C., primary optic centres, including lobus opticus, corp. genic, lat., and pulvinar of one side; F.O., fasciculus opticus (Gratiolet) in the internal capsule; C.P., cornu posterior; G.A., region of gyrus angularis; L.O.S., lobus occip. sin.; L.O.D., lobus occip. dext.; Cu., cuneus and subjacent gyri constituting the cortical visual centre in man. The heavy or shaded lines represent parts connected with the right halves of both retinae.
Indicates some additional complication. Pressure on the insensitive sides of the eye will not cause phosphenes. Ophthalmoscopic examination show no lesion, except in the later stages of the disease, when there is sometimes a paleness of the papilla.
Lateral homonymous hemianopsia usually develops suddenly and is often associated with hemiplegia, and at times diminution of the cutaneous sensibility. If on the right side of the field it may be accompanied by aphasia. The line of demarcation is usually nearly vertical at the point of fixation. Transient hemianopsia, and generally of the homonymous lateral type, has been noticed.