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.