Text book of veterinary medicine, Volume 3 (of 5)

by James Law

The tension and hardness of the bulb is materially increased in some cases but not at all perceptibly in others.

From the seventh to the tenth day the acute inflammation subsides, the lids and pupils dilate, and the deposit in the anterior chamber is rapidly reabsorbed. It may first assume a dull brownish green or brownish tint. Meanwhile the opacity of the cornea commences to clear up, and any redness or congestion of its margin to diminish or disappear.

With this disappearance of opacities in the cornea, lens and humors, all the symptoms of congestion subside and by the tenth or fifteenth day from the commencement of the attack the eye may have become approximated to its normal condition.

The characteristic of the disease, however, is its tendency to return again and again until the eye is destroyed. From five to seven attacks usually result in blindness, and then the second eye is likely to have a similar experience until both are useless. In some instances the eye which is first attacked may recover and remain well, while the second to suffer is rapidly ruined by a succession of severe attacks. The intervals between the attacks may be thirty, forty or sixty days and upward according to the state of the health, the condition, the food, the regimen, the exposure, and perhaps of other accessory causes.

Reynal claims that some eyes which have retained their normal function after one or two attacks will sometimes gradually lose the power of vision without any new appearance of inflammation. In other cases an eye which has been clear and transparent becomes suddenly filled up with an inflammatory exudation in the anterior chamber which obscures the iris and lens and in a few days vision is permanently lost, yet without conjunctivitis or apparent suffering.

Condition of the eye between attacks. After one, two or more attacks the eye is not restored to its former condition in the intervals, but continues to exhibit morbid phenomena which betray the previous existence of the disease. The recognition of such persisting lesions is all the more easy that one eye only is usually attacked at first and a comparison between this and the sound eye renders the modifications all the more patent. Even after a first attack there is usually a hazy bluish white zone round the outer margin of the cornea and this becomes more distinct after each successive attack. The faulty eye is distinctly smaller in appearance, at first because it is retracted in its sheath and later in certain cases because of actual atrophy. In proportion to the retraction of the bulb, is the protrusion of the membrana nictitans which covers a greater part of that eye than of its fellow. The upper eyelid in place of forming a continuous and regular arch shows a distinct abrupt bend between its inner and middle thirds caused by the contraction of the levator muscle. The front of the iris has lost something of its normal lustre, and the posterior chamber is liable to show an abnormally light reflection, greenish yellow or yellowish blue. Under direct illumination, lines of opacity may be detected in the aqueous humor, or in the lens, or dark filaments in the vitreous. After several attacks the lens is very distinctly obscure and this increases with each relapse to a white or yellowish white complete opacity. After the first or second attack the pupil may be distinctly contracted, while later in the disease, with advanced cataract it is usually widely dilated. Another feature is the erect, attentive carriage of the ear, to compensate for the waning vision.

Lesions. These are not often seen, as animals do not often die of this disease. Beside the superficial lesions of the conjunctiva and cornea which may be seen during life, exudates have been found on the posterior surface of the cornea, in some cases binding that to the iris. In advanced cases the greatly contracted anterior chamber may contain a little mucilaginous liquid strongly pigmented with debris from the iris, the whole mixed with shreds of exudation. The iris is thickened by congestion and by exudation on its surface and in its substance, and is displaced forward so as to diminish the size of the anterior chamber, and it may have contracted adhesions with the cornea (anterior synechia) or with the lens (posterior synechia). This leads to unevenness in the pupillary margin, where the iris is often torn into shreds. The crystalline lens is usually opaque, and may have undergone various changes, fibrous, calcareous, or atrophic. The anterior surface of its capsule has often adherent masses of black pigment derived from the urea in previous adhesions.

The vitreous humor and hyaloid membrane are sometimes clear, but usually yellowish or blackish and reduced to one-half their normal bulk by accumulations under the retina. A dense exudate often exists on the lamina cribrosa. The choroid is very uneven showing irregular rounded elevations, and like the iris is the seat of active congestion, exudation and thickening. The exudate on its surface raises and detaches the retina and, as shown by Eversbusch, this may increase so that the retina from the two sides may come together in the centre of the eye, the vitreous having been absorbed and removed. Reynal records instances in which the exudate had become cretified, or as he claimed transformed into true bony tissue. Finally the optic nerve is atrophied, often in advanced cases to half its natural thickness.

Prevention. As treatment is somewhat unsatisfactory there is the greater reason to give attention to measures of prevention.

In view of the great evil of low, damp, overflowed lands, it is important to drain and improve such lands whenever possible, and when this cannot be done, to abandon the breeding of horses upon them, and to buy the animals necessary for agricultural purposes from high, dry, healthy localities and introduce them only after they have passed the age of five years at least.