Oblique illumination, or, as it is sometimes called, focal or lateral illumination, is used as shown in Fig.2. The patient is placed two feet from the gaslight in a darkened room, as preferable to daylight, the light is then brought to a focus upon the cornea with a two or three inch lens, the surgeon may at the same time observe the surface under examination through another magnifying lens held before the eye. In order to focus the light upon the different structures, the illuminating lens will have to be moved slightly, according as the pencil of light is made to play over the cornea, iris, or lens.
Inspection of the iris may frequently reveal normal physiological differences in color or shade of the two irides; and we may also have instead of the uniform pigmentation one or more irregular spots of different color. We can also detect by the oblique illumination swelling, discolorations and vascularity of the iris tissue; the loss of lustre or the presence of gumma, foreign bodies, etc.; the shape and size of the pupil, the presence of adhesions to either the cornea or lens. The mobility of the iris should be carefully studied, as the pupils of the two eyes should act consensually; to examine, the patient is placed before a window in daylight and directed to look at a distance; one eye is then covered, the other exposed eye will contract to the bright light while the covered eye acts in harmony. If both eyes be now shaded dilatation ensues, and if then again exposed to the light contraction immediately follows, succeeded in a moment by slight dilatation and again a contraction; thus oscillating for a moment it finally settles down to its original size. This action is called hippus, and is sometimes present in a marked degree in cases of hysteria, mania, and other nervous disorders. As the pupils contract under the influences of accommodation and convergence, care must be taken during the examination that the eyes are constantly fixed on a distant object.
Dilatation of the pupil occurs in glaucoma, atrophy of the optic nerve, from fright, in anaemia, nervous conditions, etc., in young people and from the use of mydriatics. According to McEwen dilatation in diseases of the nervous system, when of cerebral origin, indicates extensive lesion, and when of spinal origin irritation of the part.
Contraction of the pupil occurs in old people, from the use of myotics, is present in inflammation of the iris, in some fevers, in mitral disease and pulmonary congestion, and in paralysis of the sympathetic. If of cerebral origin, as in meningitis, it indicates an early irritative stage of the disease; if of spinal origin, a depression, paralysis or even destruction of the part (McEwen). The Argyll-Robertson pupil is the small, contracted pupil which affected little, or none at all, by light and shade, responds by contracting still farther under the influence of convergence. This action of the pupil is found in degeneration of the posterior columns of the cord and indicates a serious central lesion.
The examination of the anterior chamber and lens also, by the aid of the oblique illumination, shows if the former is more shallow or deeper than normal, the presence of any exudation, etc., while in the lens the faintest trace of disturbance or change can be detected.
Proptosis, or protrusion of the eye, if unilateral, may be noted by comparing the position of the corneae with each other and with the brows. It is present in Graves disease, orbital diseases, intraocular tumors, paralysis of the ocular muscles, etc.
Finally the tension of the eye should be noted. To estimate the tension of the eyeballs the patient should be made to look downward and to gently close the eyes, for, if squeezed tightly together, that alone may slightly increase the tension. The index fingers of both hands should be applied to the lids, as there is not the same delicateness of touch between the first and second fingers of the same hand, and press gently first with one finger and then the other. The tension should always be estimated from palpation on the sclera some distance back of the cornea. Estimate according to the resistance or indentation of the globe. Tonometers, or instruments devised for estimating the tension have been employed, but are hardly practical for general use. The following signs are used for designating the degree of the tension, viz.: Tn, tension normal; T plus? or T-?, a doubtful increase or decrease of tension; T plus I, a marked increase as compared with normal; T plus 2, a greater increase, but the globe admits of some dimpling; T plus 3, stony hardness, or no impression from firm pressure; T-I, a decrease as compared with normal; T-2, greater loss of tension, and T-3, eye very soft, no tension at all. The tension differs physiologically in different eyes; the sclera is more elastic in young than in old people; a large eye yields more than a small one, and variations in the form of the eye affect the tension. Diseases of the sclera might increase or decrease the tension. Variations in the curvature of the sclera at the point of impression will cause a slight difference in the tension, the greater the curvature the softer the eye. The tension of one eye should always be compared with its fellow, and when in doubt with an eye known to be normal, in a person of the same age as the patient.
The Field of Vision.-By the field of vision is meant the space, when the visual axis of one eye is fixed upon some stationary point, in which all other objects are visible. This space is large or small, in proportion to the distance at which the fixation point is from the eye. The object fixed imprints its image upon the macula lutea, while the image of all other objects fall upon some peripheral portion of the retina.
Peripheral vision is of value, in that while we only see objects indistinctly upon which the visual axis is not fixed, it attracts our attention to other objects which we may desire to see, and the eye is then turned in that direction. As for example, in crossing a street our peripheral vision is attracted by the approach of a team within the field of vision and our attention is turned to it that we may avoid an accident. In many diseased conditions of the fundus a knowledge of the field of vision is of the greatest importance both in diagnosis and prognosis.
The normal field of vision varies in different directions, being greatest toward the temporal side, where it has an extent of over 90 degree because the rays from such a point, owing to the strong refraction at the surface of the cornea, can still enter the pupil. The field at the nasal side and above is of much less extent, because of the limitation caused by the nose and brow. The normal field for colors is found practically to be more contracted than that for white, and to vary with the different colors-blue being the least contracted, red next and green the most contracted.
Pathological changes in the field of vision are both numerous, varied, in many diseases, are quite characteristic. Alterations in the visual field may be concentric, uniformly drawn in at all points; sector-shaped, where it has the shape of a triangle whose base corresponds to the periphery; hemiopic, one-half of the field wanting; in addition to these more or less regular and frequently found forms of contraction there are many irregular shaped notches in the normal field. Scotomata, or blind spots in the visual field, when found as the result of disease, are classed as central or peripheral. A central scotoma involves the point of fixation, and means that direct vision is either diminished or wholly lost. Peripheral scotoma, on the other hand, do not involve direct vision and cause but little disturbance; in fact, are often not known to the patient until found in examining the field. An annular scotoma is one that more or less completely surrounds the point of fixation like a ring, the direct vision being left intact. In the healthy eye we have a scotoma, known as Mariotte`s blind spot, which corresponds to the entrance of the optic nerve and lies about 15 degree to the outside of the point of fixation.
Concentric contraction with central vision impaired, may be found in atrophy of the optic nerve or retina; with central vision good, in retinitis pigmentosa and sometimes in the early stages of glaucoma. Sector-shaped alternations may be found in atrophy of the optic nerve, in occlusion of one of the retinal arteries, in detachment of the retina, and in glaucoma the nasal side is contracted,. Scotomata are found in choroiditis disseminata and other choroidal diseases, in haemorrhages, especially when in the maculalutea, in toxic amblyopias, etc.
The importance of a careful study of the field for colors, as well as for white, is well illustrated in atrophy of the optic nerve, as in this disease the color field is more constantly involved than that for white, and in some cases will be first sign of the disease. In glaucoma the field for colors is lost with that for white, and they bear the same concentric arrangement throughout. In toxic amblyopia there is frequently found a central scotoma for red and green.
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.