RETRO-BULBAR OPTIC NEURITIS.
Definition. Neurites descendens and ascendens. Extension to bulb, other eye, or brain. Causes: traumas, meningitis, infectious diseases, toxins, lead, tobacco, etc. Symptoms: partial blindness: congestion of papilla, exudates in adjacent retina. Treatment: eliminate poisons, lead, toxins, correct precedent disease, saline laxatives, diuretics, potassium iodide, cupping, local bleeding, counter-irritants. Hygiene.
This is inflammation of the optic nerve commencing behind the eyeball and only involving the papilla secondarily. Extension to the papilla has been called neuritis descendens in contradistinction to neuritis ascendens in which the inflammation extends along the nerve toward the brain. There is always a tendency to extension, it may be to the papilla and retina, it may be to the chiasma and opposite eye, and it may be inward toward the ganglia and choroid plexus.
Causes. Apart from traumatic causes, retro-bulbar neuritis in the domestic animals has been mainly seen in connection with constitutional or infectious diseases; in the horse with petechial fever (Peters), contagious pneumonia (Schindelka), meningitis (Peters, Straub) and parotitis (Möller). It has also followed meningitis in cattle (Nebelen). In man it has been traced to lead, tobacco, alcohol and other poisons.
Symptoms. At first the patient may seem partially blind without apparent cause. Later ophthalmoscopic examination reveals congestion and swelling of the papilla, and congestion (especially venous and capillary) of the retinal vessels. The discolorations in streaks and spots, from exudates and degenerations follow as noticed under papillitis. It is difficult to distinguish between this and papillitis during life.
Treatment should be first directed toward the elimination of any poisons, such as lead or tobacco, which may act as a causative factor. Saline laxatives and in chronic cases potassium iodide would be indicated. Every attention should be given to the maintenance of good general health, and in acute attacks, local bleeding and counter-irritation may be resorted to.
ATROPHY. PARALYSIS OF THE OPTIC NERVE. AMBLYOPIA. AMAUROSIS.
Definition. Horses, dogs, cattle, sheep. Amblyopia, Amaurosis. Causes: retinal paresis from brilliant light, of cerebral ganglia, snow blindness, poisons, lead, opium, atropine, lolium, tobacco, carbon bisulphide, cryptogams, mushrooms, “loco” plants, carbon monoxide, illuminating gas, quinine, heat apoplexy, cerebral concussion, brain parasites, exudates, pressure, degeneration, gastric or intestinal disorder, hæmorrhage, anæmia, diarrhœa, diuresis, excessive milk secretion, gestation, embolism. Symptoms: constant excessive dilatation of pupil, no response to light, brilliant reflection from retina and choroid, blue or yellow, (glass eyes); bilateral, cerebral, tract or chiasma; unilateral, bulbar or nervous; face without expression, ears alert, head to one side, nose elevated, nostrils dilated, ox and dog smell ground, slow pace, high stepping, does not dodge a feint to strike. Lesions: inflammatory exudate and retinal atrophy, congested, “woolly” papilla, retro-bulbar congestion or atrophy of nerve, thickening of neurilemma, tumors of orbit or foramen optica, cœnurus, cysts, abscesses, cholesteatomata, psammomata, hydrocephalus, meningitis, pineal hypertrophy, cranial fractures or tumors, embolisms or aneurisms, hypertrophy of dura, apoplexy. Treatment: remove causes, laxatives, diuretics, for lead, sulphuric acid and potassium iodide, darkness, extract cœnurus, elevate depressed fractures, ice, cold snow, to head, blisters, setons, electricity, strychnia, remove tumors.
Blindness without adequate, corresponding, visible changes in the structure of the eye, has long been recognized in the lower animals, having been observed in horses, dogs, cattle and sheep. When partial it is known as amblyopia, and when complete as amaurosis or blindness. The term amaurosis is, however, being gradually eliminated from ophthalmological nomenclature in favor of that of atrophy.
Causes. These may be factors which act directly on the retina, as the intense light of the sun, of an electric, lime or magnesium light, of the reflection from snow, ice, water, sand, or white dust. These exhaust the power of vision by over-stimulating it, but whether the blindness is due to fatigue of the retina or of the cerebral ganglia which preside over sight, it is difficult to decide. This form is much more likely to occur in horses which spend most of their time in darkness, as in unlighted stables or mines, when they are suddenly brought into the sunlight. Snow blindness, however, from prolonged exposure, is common in animals as in man, and the case of the staghound reported by Johan, is by no means an isolated one.