CHRONIC CONJUNCTIVITIS.
Sequel of acute. Same causes. Old horses, young foals, damp lands, night dews, frosts, eczema, follicular scabies. Lesions: swelling of lymph bodies in conjunctival pouch, general congestion, chemosis, hypertrophied papillæ, clouded cornea; Symptoms: as in acute form but less intense. Treatment: Remove cause, irritants, damp soils, stables, etc., glare of light, heat, etc., astringent antiseptic lotions, atropia, mercury oxide, counter-irritation, setoning, cupping, leeching.
This is generally recognized by veterinary writers as a sequel of the acute form, though it may begin de novo, from slight persistent causes of irritation. Habitual exposure to fierce light, dusty roads, ammoniacal and other gaseous emanations, and at other times to the dust from musty fodders in a high rack, trichiasis, entropion, ectropion, and indeed any continued irritation may start the disease or keep it up. Leblanc says it is especially common in old horses and young foals pastured on low damp grounds, bottom lands and lake shores, and in worn out work oxen which have been exposed to cold night dews, or frosts. In this respect it resembles the recurring ophthalmia of the horse which prevails especially in lymphatic subjects. In dogs, Leclainche has observed it associated with eczema or follicular scabies of the lids.
Lesions. Besides the general congestion of the mucosa, there are liable to be special lesions in the depth of the conjunctival sac at the point where the mucosa passes from the eyelid to the sclerotic, causing uneven swellings from infiltration in this region. The lymph bodies or follicles in this part are swollen and project as small red or grayish nodules visible when the eyelid is everted, and at other times the whole infiltrated conjunctiva projects between the lids constituting the condition known as chemosis. The papillæ conjunctivæ are also hypertrophied, so as to become visible to the naked eye, and ulcers may be present on the mucosa. The cornea is often clouded blue or milky, or it may have become in part vascular and reddish, or even ulcerated. A more or less abundant muco-purulent discharge is always present.
Symptoms. The inflammation is usually moderate in degree, the eyes water without being habitually closed, the hairs are lost from the cheek, which is habitually wet, the lids are swollen, and like the cilia tend to stick together after sleep, and the whole mucosa is visibly infiltrated and congested, but usually especially at given points, as in the cul de sac, on the lids or membrana nictitans. Unless the animal has been treated with irritant dressings, there is much less pain on manipulation than in acute conjunctivitis. On everting the lids the folliculitis in the cul de sac and the circumscribed swellings become apparent. The membrana nictitans is partly projected over the cornea, and the eyeball usually appears smaller by reason of its retraction within the orbit.
In cases of eczema, or demodectic mange, the lesions of the skin of the eyelids will furnish the key to the trouble.
Treatment. The first object must be to remove the cause which tends to keep up the malady. Foreign bodies, musty hay fed from high racks, dusty roads, excess of light, windows in unsuitable places, damp stalls or pastures, and local parasitism must be corrected. In case of persistent chemosis keeping up the inflammation, and which will not subside under the usual astringent lotions, the hernial mucosa may be excised. (See chemosis.)
The usual astringent lotions may be employed, sulphate of zinc (2:100), sulphate of copper (1:200), alum (5:100), tannin (10:100) to which may be added sulphate of atropia. In place of being simply applied to the surface of the lids, or the cornea, it is usually desirable to inject it into all parts of the cul de sac beneath the upper and lower lids and beneath the nictitating membrane. Alum 4 grs. and boric acid 3 grains, in water 1 oz. make a good combination. As the mucosa becomes accustomed to one agent, we may change for another. Thus in addition to the above, silver nitrate (2:100), and lead acetate (2:100) are often useful as alternates. In obstinate cases red or yellowish oxide of mercury in vaseline (5:100) may be applied inside the lids and on their margins.
Counter-irritation is often desirable, in the horse a blister of cantharides or mercury biniodide to cover a spot as large as a silver dollar above the anterior end of the maxillary spine (zygomatic), or a stout silk thread as a seton inserted in the same place. In the dog the blister may be applied on the temporal region.
Cupping or leeching beneath the eye, or phlebotomy from the angular vein of the eye may prove useful. Great care should be taken to prevent further injury by rubbing.