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.
Mauthner says in right homonymous hemianopsia the right optic nerve will appear atrophic, while the left remains normal. Blindness of the right side of the field causes more trouble in reading than when the left side is gone. Central vision may be either perfect or impaired.
Homonymous lateral hemianopsia results from intra-cranial and generally cerebral disease, which may be either tumors, haemorrhage, embolisms, injuries, softening, etc. The seat of the lesion may be in any part of the visual tract between the eyeball and the cortex of the brain.
The explanation as to the path through which pathological lesions result in the various forms of hemianopsia has been the subject of prolonged investigation and discussion. The accompanying diagram illustrating the visual paths and their relation to the visual field will give all that seems necessary here. Fuller details in the study of this subject falls under the domain of the neurologist to whom the student is referred.
As to the nature of the lesion, the diagnosis must depend upon the history, nature of the attack and concomitant symptoms; but in all cases of cerebral disease, especially where the ophthalmoscope reveals no lesion, the visual field should be examined.
PROGNOSIS.-Restoration of the visual field is rare, but when it does occur, it is apt to be symmetrical in both eyes. If both hemiplegia and hemianaesthesia are present, the former may disappear and the latter remain. The hemianopsia is usually but one of other cerebral symptoms which may end in death. Nasal homonymous hemianopsia generally affords a better prognosis than temporal.
TREATMENT.- Half vision is usually only a symptom of some deep disorder of the eye, but as it is sometimes the only symptom to be found those remedies appropriate to it will be mentioned: Upper half of visual field defective: Aurum, Digitalis and Gelsemium
Right half of visual field defective: Cyclamen. Lithium carb. carb. and Lyco.
Vertical hemiopia, either half invisible: Calcarea carb., China sulph., Acid Muriaticum, Nat. mur., Rhus, Sepia, and Stramonium
Professor of Ophthalmology in the College of the New York Ophthalmic Hospital; Surgeon to the New York Ophthalmic Hospital. Visiting Oculist to the Laura Franklin Free Hospital for Children; Ex-President American Homoeopathic Ophthalmological, Otological and Laryngological Society. First Vice-President American Institute of Homoeopathy : President Homoeopathic Medical Society of the State of New York ; Editor Homoeopathic Eye. Ear and Throat Journal : Associate Editor. Department of Ophthalmology, North American Journal of Homoeopathy, etc.