ACUTE KERATITIS. INFLAMMATION OF THE CORNEA.
Extension from conjunctivitis, wounds, foreign bodies, bites, stings, blows, infections, filaria. Symptoms: eye tender, closed, epiphora, red, pannus, photophobia, congested sclera, opaque or ramified red cornea, or diffuse red, exudation, suppuration, corneal abscess, ulcer, perforation, prolapsus iris, panophthalmia. Focal illumination. Recovery. Permanent cicatrix or opacity. Lesions: exudates of lymph and leucocytes into corneal layers: embryonic tissue: vascularization: abscess: ulcer: cicatrix: opacity: staphyloma: hypopion: prolapsus iridis: panophthalmia. Treatment: antiseptic astringents, atropine, leeching, derivatives, blister, seton, opacities; in severe cases antiseptic puncture, sublimate lotion, silver nitrate, potassium permanganate, boric acid, pyoktannin: in perforations antiseptic bandage and eserine, iridectomy: in chronic cases mercury oxide.
Keratitis occurs in all domestic animals as a primary disease, or as an extension from conjunctivitis.
Causes. Extension from acute, enzootic, infectious conjunctivitis in sheep and cattle has been noticed by a great number of observers. Bayer and Lohoff have studied maculated keratitis of the superficial layers in horses. Again it has followed wounds by foreign bodies, spikes of vegetables, particles of iron and glass, blows of whips, or insects, stings, etc. It also occurs in connection with the local action of particular poisons, such as variola (foot and mouth disease), canine distemper, etc., and from the local irritations caused by trichiasis or entropion or by the filariæ lachrymalis (ox) and palpebralis (horse).
Symptoms. The eye is extremely sensitive, and habitually closed, with a profuse flow of tears, and a disposition to resist opening of the lids. When exposed the cornea is seen to be more or less clouded and perhaps reddened by the formation of vessels proceeding from its sclerotic margin. This is known as pannus. If the anterior chamber is still visible the pupil is found to be contracted showing photophobia. The congestion is first visible in the sclerotic and in the absence of pigment is most intense near the margin of the cornea. Upon the cornea itself it is preceded by a deep white opacity, into which the vascularity gradually extends. The whole cornea may finally become of a bright pink hue.
The congestion of the cornea may advance to fibrinous exudation, or the formation of pus between its layers, to molecular degeneration and the formation of ulcer, or even to perforation and escape of the aqueous humor. In this case prolapsus iris, panophthalmia and destruction of the eye are likely to ensue.
Ulcer if not readily seen with unaided vision can be easily recognized by the aid of focal illumination, and abscess can be detected by the presence of a sharply circumscribed centre of intense opacity, white or yellow, and some bulging of the membrane.
The pus may be absorbed, or it may escape by rupture and discharge externally, or into the anterior chamber when the resistance is least in that direction, and when this takes place, a dangerous internal infective inflammation is the result.
In the slighter forms of keratitis the inflammation may come early to a standstill, and recede, tenderness and photophobia pass off, the eyelids may be opened, and the corneal opacities gradually disappear. If any portion of the cornea has become vascular, that portion is liable to remain opaque or even pink.
Lesions. Under the influence of an irritant on the cornea, the vessels in the margin of the sclerotic become actively congested and pour out lymph freely, leucocytes also escape and with the lymph pass through the lymph channels into the substance of the corneal tissue. Here they undergo active fission and increase, and the normal cells of the corneal tissue multiply in like manner, so that in a short time there is an extraordinary production of embryonic cells. Into the embryonic tissue so formed, blood escapes from forming loops of new vessels, and this goes on extending until the whole cornea may have become vascular. Degenerations in the newly formed structure may result in suppuration, (hypopyonkeratitis) or molecular decay and ulceration, (ulcus corneæ) or organization may take place into the fibrous tissue with contraction and permanent opacity, (macula) or a hyperplasia may form in the shape of a staphyloma.