Part 58

6th. =The pupil should promptly and freely respond to light and darkness by contraction and expansion.= Absence or tardiness of movement indicates impaired vision, from disease of the eye, its nerves, or their nerve centres.

7th. =Each cornea should have a median convexity, uniform in all directions implying the absence of myopia, preshyopia and astigmatism.= Any deviation from this will interfere with the perfection of sight, and endanger shying and other troubles.

8th. =Under ordinary light the pupil should appear black throughout.= In the larger animals such dilation of the pupil as to expose the tapetum lucidum under such circumstances implies impaired vision (amblyopia, amaurosis), inflammation of the iris or undue intraocular pressure. A white color or spot shows cataract.

9th. =The lids must be open and mobile without excessive dilation.= Tardily moving or semi-closed lids, distorted by scar or angle, everted or inverted, are unattractive and usually imply disease in the eye, nerves or brain.

10th. =The unpigmented portion of the sclera should be light pink.= The dark red of congestion and the pallor of anæmia are equally objectionable.

11th. =The tears must be clear, limpid and confined within the lower lid.= Any milkiness, flocculency or overflow is indicative of disease.

12th. =The eyelids must be thin, delicate, evenly and uniformly curved along the borders, and fringed by an abundance of strong, prominent and well directed lashes.= Puffiness or swelling betrays inflammation, dropsy, anæmia, parasitism or other disorder, angularity of the upper lid an internal ophthalmia, and depilation or wrong direction of the lashes, local disease.

13th. =The eye should respond instantly, by movement, to new objects and noises, without showing undue irritability or restlessness.= The intelligent apprehension of the objects will introduce an aspect of calmness and docility.

DEFECTS, BLEMISHES AND ABNORMALITIES OF THE HORSE’S EYE.

Some of these may be present in the absence of actual disease, and yet prove so objectionable that they disqualify the animal for any use, in which style or æsthetic appearance is demanded. Among such sources of disqualification may be noted:

1st. =The small eye.= One or both eyes may appear small because of internal pain and retraction within their sockets, or from actual atrophy or contraction of the eyeball, the result of deep seated disease, or the organ may be congenitally small, and deep seated in the orbit, and the thick tardy eyelids may have a narrow opening through which they can only be partially seen. This last condition usually implies a dull lymphatic constitution, low breeding and a lack of intelligence, docility and vigor.

2d. =The semi-closed eye with thick, coarse, sluggish lids.= In this case the bulb may be not unduly small, yet as it is not freely exposed it conveys the same general expression to the observer. Like the small eye it indicates low breeding, lack of intelligence or docility and often stubbornness or even vice.

3d. =The convex eye.= In this the transparent cornea describes the arc of an unduly small circle, suggesting a conical form and projecting unduly beyond the margins of the lids. It implies imperfect vision, myopia, and, it is alleged, low breeding and lack of alertness.

4th. =The sunken eye.= This has been already referred to under =the small eye=. The eyelids are usually flaccid, the upper being drawn in by its levator so as to form an angle, and the edges of the orbit are somewhat prominent. It is seen in old, worn out animals, which have lost the pads of fat in the depth of the orbit, and more commonly in animals that have suffered several attacks of recurrent ophthalmia.

5th. =The projecting eye.= In this case the lids are unduly contracted and the eye protrudes between them so as to show a large amount of sclerotic around the transparent cornea. This may be due to nervous strain and suffering but, however produced it is decidedly unsightly and objectionable.

6th. =The weeping eye.= This is always a condition of disease. It may be due to irritant gases, or solid particles, to inturned cilia, everted lids, conjunctivitis or a variety of other conditions. A careful examination may show whether it is only a transient and remediable fault of a good eye or a permanent and irremediable defect.

7th. =The blear eye.= With swelling and scabbing of the edges of the lids and Meibomian glands, and congestion of the adjacent conjunctiva, there is usually some blurring of the surface of the transparent cornea. The trouble is mostly chronic and constitutes a serious objection.

8th. =The watch eye.= In this, as in the albino, there is a lack of pigment, so that the iris and sclerotic are white or bluish white in part or in whole. Such an eye may be good and durable, but not beautiful nor attractive.

9th. =Blindness of one or both eyes.= In all such cases the pupil remains fixed and immovable, showing no accommodation to light and darkness, and there is a lack of prompt responsiveness on the part of the eye to sounds and objects. In amaurosis, glaucoma and cataract especially, the pupil remains widely open, and alert movements of the ears are employed to make up for the lack of sight. The condition often comes from internal ophthalmia, such as the recurrent form, and is associated with atrophy of the bulb.

10th. =Eyes of unequal size.= This usually implies serious disease in one, not infrequently recurring ophthalmia.

11th. =Too flat corneal surface.= In this case there is a manifest lack of the normal projection, the anterior surface of the cornea describing the arc of a larger circle, the visual rays coming from a distance alone converge on the retina and presbyopia occurs. In this as in myopia and other visual imperfections a horse is liable to stumble and, if nervous, to shy.

12th. =Ovoid Cornea.= In such cases the front of the transparent cornea has an ovoid outline the arc formed by it in one direction being that of a greater circle, than the arc which crosses this at right angles. In consequence of this, the rays impinging on the outer portions of these respective arcs do not converge to the same point on the retina and a blurred and imperfect image results. This astigmatism causes the subject to stumble and, if nervous, to shy.

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.