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.
Much more common are factors which act primarily on the nerve centres.
Poisoning with lead, poppy, belladonna (sheep and goats, Gerlach),
lolium temulentum (Klüver), tobacco, carbon bisulphide, cryptogams
(musty fodder), mushrooms, astragalus mollissimus, etc., abolishes
vision more or less perfectly. Common illuminating gas and carbon
monoxide have shown this effect on dogs and chickens. Quinia subcutem
has induced the condition in dogs (Becker and Eversbusch). More or less
complete amaurosis is noticed in connection with heat apoplexy in horses
and fat cattle.
Cerebral concussion from blows on the head, knocking the head against a
post or wall, or from violent falls induce blindness which is to be
attributed rather to lesion of the brain. The same remark applies to
cases that appear during the progress of brain disease, parasitic or
otherwise, to those that occur in connection with overloading of the
stomach or intestines, and from gestation (Riss).
In cases appearing after severe depletion, like profuse hæmorrhage,
diarrhœa, or diuresis, or excessive secretion of milk (bitch), the
anæmia of both eye and brain may be taken into account.
When amaurosis develops during some inflammatory or infectious disease,
as in parturition fever in cows, the immediate cause may sometimes be
found in embolism of the retinal, or cerebral arteries.
_Symptoms._ The most striking feature of amaurosis is the constant
excessive dilatation of the pupil. This is the same in light and
darkness, and in fully developed cases the animal may be taken from
perfect darkness to the full glare of sunlight or electric light without
the slightest contraction of the pupil. The pupillary reflex to light is
entirely lost. In the slighter cases (amblyopia) there remains some
slight response of the iris to light but always far short of the normal.
The widely dilated pupil admits a flood of light, and in the absence of
cataract, lights up the chamber of the vitreous to an unusual degree.
The blue or yellowish reflection of the tapetum is very striking, and
led to the obsolete names of gutta serena and glass eyes. Sometimes the
disease is unilateral and at others bilateral. In case it is unilateral
there is a strong presumption that the causative lesion is in the
affected eye or in the optic nerve in front of the chiasma. In the
bilateral cases it is more likely to depend on disease of the brain or
some more distant organ.
Certain important indications are to be drawn from the expression of the
face, the position of the head and ears and the mode of locomotion. In
all blind animals the face is without expression. The dilated pupils
give no suggestion of mind looking through them, they have on the
contrary an uniform stony stare. There is no sense of fire or life, but
the face is like a dull sculptured mass. The immobile face finds a sharp
contrast in the alertness of the ears, which may be carried one forward
and another back, but fixed and yet ready to turn to catch every sound.
In the horse the head is usually carried a little to one side for the
same reason, and with the nose elevated (_star-gazer_) and nostrils
dilated. The ox inclines to carry the head low, while the dog keeps his
nose near the ground to guide himself by the sense of smell. All blind
animals are disposed to move slowly and carefully, and the horse
acquires a habit of _high stepping_ to avoid stumbling.
A common and important test where both eyes are equally affected and
cannot be contrasted with each other, is to strike the lower part of the
face with the hand and immediately threaten to repeat the blow. If the
animal can see, it will seek to jerk the head out of the way as soon as
the hand is raised for the second blow, while if blind there will be no
such movement provided the motion of the hand has not been such as to
induce a current of air on the face.
_Lesions._ Blindness, or the general symptoms of amblyopia or amaurosis,
may attend on the atrophy of the retinal fibres in connection with
inflammatory exudation or blood extravasation on, in, or beneath, the
retina. In other cases the lesion is in the papilla which is inflamed
and swollen with the woolly aspect characteristic of choked disc. In
others there is congestion of the optic nerve behind the bulb, with
exudation into its substance or beneath its sheath, or the nerve has
already undergone extensive atrophy with thickening of its neurilemma.
In other cases there is atrophy of the arteria centralis retinæ, or
tumors of the orbit or optic foramen pressing upon the nerve. Cases of
this kind are reported in the larger animals by Leblanc and Tscheulin,
and in dogs and ducks by Hilbert.
Much more frequently the determining lesions are situated in the brain
or its meninges. In sheep it is very common from the development of
cœnurus cerebralis over the optic lobes. Kühnert found a cyst with
delicate walls in the brain of a horse affected in this way. Amaurosis
is occasionally seen in connection with the cerebral abscesses which
form in complicated cases of strangles or in pyæmia, also in cases of
cholesteatoma of the choroid plexus. Other conditions of its occurrence
are hydrocephalus, meningitis, hypertrophy of the pineal gland, fracture
of the cranium, tumors of the cranium or dura mater, embolism or
aneurism of the cerebral arteries, hypertrophy and induration of the
dura mater (ox, Leblanc), or sanguineous apoplexy. In a certain number
of cases there may be no lesion of brain or eye, or only a congestion of
the former in connection with lead poisoning, rye grass poisoning or
other gastric disorder, or of gestation.
_Treatment._ Success will depend on the sympathetic nature of the
condition or on the transient and removable character of its causative
factor. When the condition is but a symptom of overloaded stomach or a
transient poisoning by vegetable or mineral agents a direct recovery may
be expected to follow their disuse and elimination from the system. This
may be hastened by the exhibition of laxatives and diuretics, and in the
case of lead by sulphuric acid followed by iodide of potassium. In cases
of snow blindness it is only necessary as a rule to place the animal in
the shade until the over-stimulation shall have subsided. In all these
cases the attack has come on abruptly and without any local symptom of
ocular hyperæmia and this with the preservation of the general senses
can always be looked on as a favorable indication.
In cases that come on slowly and which are accompanied by symptoms of
vascular disturbance or structural changes in the eye, or brain,
treatment is likely to be less successful. Nevertheless cœnurus may be
removed by surgical means, depressed fractures may be elevated, and
acute cerebral and meningeal congestions may be met by appropriate
measures. If the cerebral congestion is acute, free bleeding from the
jugular with a strong purgative and the application of ice or cold water
to the head may prove useful. Apparent benefit has also followed the use
of blisters on the face or back of the ear, of setons, and later of a
weak electric current and strychnia. Tumors also may be advantageously
removed.
But in cases marked by destruction of the retina or papilla, by
congestion or atrophy of the optic nerve, by destructive disease of the
optic foramen, or of the brain or its meninges, treatment is futile.