A Manual of the Diagnosis And Treatment of the Diseases of the Eye

of the field of vision and the periphery remain normal, or less impaired than a ring-like area surrounding the center of the field. It may possibly be due to a lesion affecting a special portion of the optic nerves or tracts, but generally it is caused by disease in the corresponding portions of the choroid and retina. Most frequently, scotomas are single, or arranged without symmetry ; they may be permanent or quite transient. The latter will be referred to in connection with transient impairment of vision. Narrowing of the field of vision is the most significant symptom of atrophy of the optic nerve and certain allied affections. It is ascertained by testing the field of vision with the hand or with a perimeter. Symmetrical narrowing points to primary atrophy of the optic nerve or to the effects of certain poisons. [See Quinin Blindness, Chapter XIII.] It is apt to affect the field of vision for colors before there is any notable change in the field for form. Irregular narrowing of the field, which may also affect the field for colors more than the field for form, is indicative of secondary optic atrophy, or injury to the tracts as by glaucoma, optic neuritis, etc. Inconstant impairment of vision after the eyes have for some time been used for close work, occurring particularly in the latter part of the day, or when the eyes are used by artificial light in the evening, is caused by the sudden relaxation of the accommodation, after the ciliary muscle has been...