SYSTEMATIC INSPECTION OF THE EYE.
System in Examination. Eyelids: cilia: lachryneal puncta: mucosa, light pink, brick red, yellow, puffy, dropsical: Ciliary vessels deep, immovable; nictitans; transparent cornea equally smooth, glossy, with clear image at all points: foreign body on cornea: corneal ulcer: opacities in aqueous humor: iris and pupil: corpora nigra: changes in passing from darkness to light: pupillary membrane: adhesions of iris: intraocular pressure: contracted pupil: hole in iris. Oblique focal illumination of cornea, aqueous humor, iris, lens, Purkinje-Sanson images.
In examining animals for soundness and especially the horse or dog, the condition of the eye must be made one of the most important subjects of inquiry, as a disease or defect may render the animal altogether unsuited to the object to which it is destined. As in every other field of diagnosis thoroughness is largely dependent on the adoption of a system which will stand in the way of any flaw being too hastily overlooked. Many of the points to be noted will be decided at a glance, yet this does not obviate the necessity of turning over in the mind, in succession, the different points of inquiry, and directing the necessary attention, however hastily, to each in turn. The following points should be observed:
1st. Are the eyelids swollen, hypertrophied or faulty in form, position or movements. Faults as thus indicated may imply any one of a great variety of disorders which should be followed out to their accurate diagnosis. It may be bruises, lacerations, punctures, parasites, conjunctivitis, keratitis, dropsy, anæmia, hepatic or intestinal parasitism, nephritis, paresis, entropion, ectropion, etc.
2d. Inspect the cilia as regards form, size and direction. Absence or wrong direction may imply disease of the Meibomian glands, infective inflammation, demodex or other acarian infesting, or turning in or out in inflammatory conditions.
3d. See that the lachrymal puncta are open and that there is no overdistension of the sac. The overflow of tears and the swelling of the caruncle and of the area beneath it will often indicate such trouble. In its turn it may imply inflammation of the duct, and obstruction by the tenacious muco-purulent product, or it may imply merely obstruction of its lower end by a dried scab. This last may be seen in the horse, on the floor of the false nostril at the line of junction of the skin and mucosa, and in the ass, higher up on the inner side of the ala nasi. In exceptional cases it may be desirable to pass a stilet through the canal from the puncta downward or from below upward to determine whether it is pervious.
4th. Determine the vascularity of the conjunctiva. When free from pigment as it habitually is in pigs and birds this is easily done, while in animals like the horse, in which the bulbar portion, which covers the sclerotic, is largely pigmented, we can scrutinize only the pigment free parts. In health there should be only a few, fine, pink vessels which move with the mucosa when pressed aside on the bulb. In congestion the surface may appear brick red, and the vessels are irregular, large, tortuous and are seen to anastomose at frequent intervals. These move on the bulb when pressed. The congestion is usually deepest on the palpebral mucosa and in the cul de sac, and may be whitened for an instant by pressure through the eyelid. To expose the conjunctiva the right fore finger and thumb may be pressed on the upper and lower lids respectively of the left eye, and the left finger and thumb for the right, allowing them to slide backward above and below the eyeball. Another method is to seize the cilia and edge of the upper eyelid between the finger and thumb, and draw it downward and outward from the bulb, and then deftly invert it over the tip of the finger. In the old the unpigmented conjunctiva may appear yellow from the presence of subconjunctival fat, or this may appear at any age from hepatic disease (distomatosis) or icterus. It is swollen, or dropsical in anæmia, distomatosis, etc.
5th. Examine the ciliary vessels whether they are congested or not. These are distinguished from the conjunctival vessels in that they radiate in straight lines outward from the margin of the transparent cornea and do not move on the sclerotic under pressure. They are enlarged and very red in congestion of the ciliary circle and in iritis. In eyes devoid of pigment over the sclerotic, there is usually a circular, narrow, white zone between the congested area and the margin of the transparent cornea.
6th. Examine the Membrana Nictitans. See that its free margin is uniformly smooth, even, and thin and that there is no swelling, congestion nor morbid growth on any part of the structure.
7th. See if the transparent cornea is perfectly and uniformly smooth, transparent and glistening and if it reflects clear, erect images of all objects in front of it. The image of a round object which shows any irregularity in the curvature of its margin implies a deviation from an uniform curvature of the cornea: the image narrows in the direction of the smaller arc and broadens in the direction of the larger one (see keratoscopy, and corneal astigmatism).
8th. A foreign body on or in the cornea may be recognized in a good light, but better and more certainly under focal oblique illumination (see this heading).
9th. A corneal ulcer may be similarly recognized. It is made more strikingly manifest by instilling into the lower cul de sac a drop of a solution of fluorescin and rubbing it over the eye by moving the eyelids with the finger. This will stain the whole cornea. If now the excess of stain is washed away by a few drops of boric acid, the healthy part of the cornea is cleared up and the ulcer retains a bright yellowish green tint.
10th. Opacity or Floating objects in the aqueous humor (flocculi of lymph, pus, pigment, blood, worms) are always to be looked for. They may be detected by placing the eye in a favorable light. They may be still more clearly shown under focal illumination (see below).
11th. Changes in the iris and pupil may also be noticed in a good light. The surface should be dark in the horse, and of the various lighter shades in the smaller animals, but in all alike clear, smooth and polished, without variation of shade in spots or patches and without bulging or irregularity at intervals. Apart from the congenital absence of pigment in whole or in part, which may be found in certain sound eyes, a total or partial change of the dark iris of the horse to a lighter red, brown or yellow shade implies congestion, inflammation, or exudation. The corpora nigra in the larger quadrupeds should be unbroken, smooth, rounded, projecting masses outside the free border of the upper portion of the iris. It should show a clear, polished surface like the rest of the iris. The pupil should be evenly oval with its long diameter transversely (horse, ruminant), circular (pig, dog, bird), or round with an elliptical outline on contracting and the long diameter vertical (cat). It should contract promptly in light and dilate as quickly in darkness. Place the patient before a window, cover one eye so as to exclude light, then cover the other eye with the hand and quickly withdraw. The pupil should be widely dilated when the hand is withdrawn and should promptly contract, and it should actively widen and narrow alternately until the proper accommodation has been secured. Any failure to show these movements implies a lesion in the brain, optic nerve, or eye which impairs or paralyzes vision, interferes with accommodation or imprisons the iris. In locomotor ataxia the pupil contracts in accommodation to distance, but not in response to light.
12th. Other causes of pupillary immobility include: (a) Permanence of a pupillary membrane, which has remained from the fœtal condition and may be recognized by oblique focal illumination and invariability of the pupil: (b) Adhesion of the iris to the capsule of the lens—complete or partial—in the latter case the adherent portion only remains fixed, while the remainder expands and contracts, giving rise to distortions and variations from the smoothly curved outline: (c) Adhesion of the iris to the back of the cornea—complete or partial—and leading to similar distortions: (d) Glaucoma in which intraocular pressure determines a permanent dilatation of the pupil and depression of the optic disc: (e) The pupil is narrowed in iritis, and is less responsive to atropia or other mydriatic: (f) Lesions of the oculo-motor nerve may paralyze the iris and fix the pupil. The first three and the fifth of these conditions may be recognized by the naked eye, alone, or with the aid of focal illumination, the fourth may require the aid of the ophthalmoscope and the sixth which cannot be reached by such methods, might in exceptional cases be betrayed by other disorders of the oculo-motor nerve (dropping of the upper eyelid, protrusion of the eyeball, squinting outward).
13th. Coloboma (fenestrated iris), and lacerated iris are recognizable by the naked eye in a good light, or by the aid of focal illumination.
14th. Tension of the eyeball (Tonometry). Elaborate instruments constructed for ascertaining ocular tension are of very little use in the lower animals. The simplest and most practicable method is with the two index fingers placed on the upper lid to press the eyeball downward upon the wall of the orbit using the one finger alternately with the other as if in search of fluctuation. The other fingers rest on the margin of the orbit. All normal eyes have about the same measure of tension and one can use his own eye as a means of comparison. The educated touch is essential. In increased tension, the sense of hardness and resistance, and the indisposition to become indented on pressure is present in the early stages of internal ophthalmias (iritis, choroiditis, retinitis), phlegmon of the eyeball, glaucoma, hydrophthalmos, and tumors of the bulb.