System in Examination. Eyelids: cilia: lachryneal puncta: mucosa,
light pink, brick red, yellow, puffy, dropsical: Ciliary vessels deep,
immovable; nictitans; transparent cornea equally smooth, glossy, with
clear image at all points: foreign body on cornea: corneal ulcer:
opacities in aqueous humor: iris and pupil: corpora nigra: changes in
passing from darkness to light: pupillary membrane: adhesions of iris:
intraocular pressure: contracted pupil: hole in iris. Oblique focal
illumination of cornea, aqueous humor, iris, lens, Purkinje-Sanson
images.
In examining animals for soundness and especially the horse or dog, the
condition of the eye must be made one of the most important subjects of
inquiry, as a disease or defect may render the animal altogether
unsuited to the object to which it is destined. As in every other field
of diagnosis thoroughness is largely dependent on the adoption of a
system which will stand in the way of any flaw being too hastily
overlooked. Many of the points to be noted will be decided at a glance,
yet this does not obviate the necessity of turning over in the mind, in
succession, the different points of inquiry, and directing the necessary
attention, however hastily, to each in turn. The following points should
be observed:
1st. =Are the eyelids swollen, hypertrophied or faulty in form, position
or movements.= Faults as thus indicated may imply any one of a great
variety of disorders which should be followed out to their accurate
diagnosis. It may be bruises, lacerations, punctures, parasites,
conjunctivitis, keratitis, dropsy, anæmia, hepatic or intestinal
parasitism, nephritis, paresis, entropion, ectropion, etc.
2d. =Inspect the cilia as regards form, size and direction.= Absence or
wrong direction may imply disease of the Meibomian glands, infective
inflammation, demodex or other acarian infesting, or turning in or out
in inflammatory conditions.
3d. =See that the lachrymal puncta are open and that there is no
overdistension of the sac.= The overflow of tears and the swelling of
the caruncle and of the area beneath it will often indicate such
trouble. In its turn it may imply inflammation of the duct, and
obstruction by the tenacious muco-purulent product, or it may imply
merely obstruction of its lower end by a dried scab. This last may be
seen in the horse, on the floor of the false nostril at the line of
junction of the skin and mucosa, and in the ass, higher up on the inner
side of the ala nasi. In exceptional cases it may be desirable to pass a
stilet through the canal from the puncta downward or from below upward
to determine whether it is pervious.
4th. =Determine the vascularity of the conjunctiva.= When free from
pigment as it habitually is in pigs and birds this is easily done, while
in animals like the horse, in which the bulbar portion, which covers the
sclerotic, is largely pigmented, we can scrutinize only the pigment free
parts. =In health= there should be only a few, fine, pink vessels which
move with the mucosa when pressed aside on the bulb. =In congestion= the
surface may appear brick red, and the vessels are irregular, large,
tortuous and are seen to anastomose at frequent intervals. These move on
the bulb when pressed. The congestion is usually deepest on the
palpebral mucosa and in the _cul de sac_, and may be whitened for an
instant by pressure through the eyelid. To expose the conjunctiva the
right fore finger and thumb may be pressed on the upper and lower lids
respectively of the left eye, and the left finger and thumb for the
right, allowing them to slide backward above and below the eyeball.
Another method is to seize the cilia and edge of the upper eyelid
between the finger and thumb, and draw it downward and outward from the
bulb, and then deftly invert it over the tip of the finger. In the old
the unpigmented conjunctiva may appear yellow from the presence of
subconjunctival fat, or this may appear at any age from hepatic disease
(distomatosis) or icterus. It is swollen, or dropsical in anæmia,
distomatosis, etc.
5th. =Examine the ciliary vessels whether they are congested or not.=
These are distinguished from the conjunctival vessels in that they
radiate in straight lines outward from the margin of the transparent
cornea and do not move on the sclerotic under pressure. They are
enlarged and very red in congestion of the ciliary circle and in iritis.
In eyes devoid of pigment over the sclerotic, there is usually a
circular, narrow, white zone between the congested area and the margin
of the transparent cornea.
6th. =Examine the Membrana Nictitans.= See that its free margin is
uniformly smooth, even, and thin and that there is no swelling,
congestion nor morbid growth on any part of the structure.
7th. =See if the transparent cornea is perfectly and uniformly smooth,
transparent and glistening and if it reflects clear, erect images of all
objects in front of it.= The image of a round object which shows any
irregularity in the curvature of its margin implies a deviation from an
uniform curvature of the cornea: the image narrows in the direction of
the smaller arc and broadens in the direction of the larger one (see
keratoscopy, and corneal astigmatism).
8th. =A foreign body on or in the cornea= may be recognized in a good
light, but better and more certainly under focal oblique illumination
(see this heading).
9th. =A corneal ulcer= may be similarly recognized. It is made more
strikingly manifest by instilling into the lower _cul de sac_ a drop of
a solution of fluorescin and rubbing it over the eye by moving the
eyelids with the finger. This will stain the whole cornea. If now the
excess of stain is washed away by a few drops of boric acid, the healthy
part of the cornea is cleared up and the ulcer retains a bright
yellowish green tint.
10th. =Opacity or Floating objects in the aqueous humor= (flocculi of
lymph, pus, pigment, blood, worms) are always to be looked for. They may
be detected by placing the eye in a favorable light. They may be still
more clearly shown under _focal illumination_ (see below).
11th. =Changes in the iris and pupil= may also be noticed in a good
light. The surface should be dark in the horse, and of the various
lighter shades in the smaller animals, but in all alike clear, smooth
and polished, without variation of shade in spots or patches and without
bulging or irregularity at intervals. Apart from the congenital absence
of pigment in whole or in part, which may be found in certain sound
eyes, a total or partial change of the dark iris of the horse to a
lighter red, brown or yellow shade implies congestion, inflammation, or
exudation. The =corpora nigra= in the larger quadrupeds should be
unbroken, smooth, rounded, projecting masses outside the free border of
the upper portion of the iris. It should show a clear, polished surface
like the rest of the iris. =The pupil= should be evenly oval with its
long diameter transversely (horse, ruminant), circular (pig, dog, bird),
or round with an elliptical outline on contracting and the long diameter
vertical (cat). It should contract promptly in light and dilate as
quickly in darkness. Place the patient before a window, cover one eye so
as to exclude light, then cover the other eye with the hand and quickly
withdraw. The pupil should be widely dilated when the hand is withdrawn
and should promptly contract, and it should actively widen and narrow
alternately until the proper accommodation has been secured. Any failure
to show these movements implies a lesion in the brain, optic nerve, or
eye which impairs or paralyzes vision, interferes with accommodation or
imprisons the iris. In locomotor ataxia the pupil contracts in
accommodation to distance, but not in response to light.
12th. =Other causes of pupillary immobility= include: (a) Permanence of
a pupillary membrane, which has remained from the fœtal condition and
may be recognized by oblique focal illumination and invariability of the
pupil: (b) Adhesion of the iris to the capsule of the lens—complete or
partial—in the latter case the adherent portion only remains fixed,
while the remainder expands and contracts, giving rise to distortions
and variations from the smoothly curved outline: (c) Adhesion of the
iris to the back of the cornea—complete or partial—and leading to
similar distortions: (d) Glaucoma in which intraocular pressure
determines a permanent dilatation of the pupil and depression of the
optic disc: (e) The pupil is narrowed in iritis, and is less responsive
to atropia or other mydriatic: (f) Lesions of the oculo-motor nerve may
paralyze the iris and fix the pupil. The first three and the fifth of
these conditions may be recognized by the naked eye, alone, or with the
aid of focal illumination, the fourth may require the aid of the
ophthalmoscope and the sixth which cannot be reached by such methods,
might in exceptional cases be betrayed by other disorders of the
oculo-motor nerve (dropping of the upper eyelid, protrusion of the
eyeball, squinting outward).
13th. =Coloboma= (_fenestrated iris_), and =lacerated iris= are
recognizable by the naked eye in a good light, or by the aid of focal
illumination.
14th. =Tension of the eyeball= (_Tonometry_). Elaborate instruments
constructed for ascertaining ocular tension are of very little use in
the lower animals. The simplest and most practicable method is with the
two index fingers placed on the upper lid to press the eyeball downward
upon the wall of the orbit using the one finger alternately with the
other as if in search of fluctuation. The other fingers rest on the
margin of the orbit. All normal eyes have about the same measure of
tension and one can use his own eye as a means of comparison. The
educated touch is essential. In increased tension, the sense of hardness
and resistance, and the indisposition to become indented on pressure is
present in the early stages of internal ophthalmias (iritis,
choroiditis, retinitis), phlegmon of the eyeball, glaucoma,
hydrophthalmos, and tumors of the bulb.
Oblique Focal Illumination.
This is so essential to clear and definite conclusions and is so easily
practiced on the domestic animals that every veterinarian should make
himself familiar with the method. The method is based on the fact that
when two perfectly transparent media touch each other a reflection of
luminous rays takes place only at the surface. But in case any opacity
exists in any part of the thickness of one of these media, it reflects
the rays from its surface no matter what may be its position in the
medium. Thus corneal opacities appear as gray blotches and under careful
focal illumination it may be determined whether these are on the
conjunctival surface, in the superficial or deeper layers of the cornea
or in the membrane of Descemet. Similarly cloudiness or floating objects
in the aqueous, reflect the luminous rays, and so with opacities in the
lens or its capsule, or in the vitreous. In the same way the surface of
the iris and corpora nigra may be carefully scrutinized. For
satisfactory examination of the media, back of the iris, the pupil
should be first dilated, by instillation under the lid of a drop or two
of a 3 per cent. solution of atropia, and the examination proceeded with
twenty minutes later. Homatropin is preferable to atropin as being less
persistent in its action, and less liable to produce conjunctivitis. If
it fails to produce the requisite dilatation, it may be followed by a
drop of a 4 per cent. solution of hydrochloride of cocaine, which will
secure a free dilatation, lasting only for one day in place of seven
days as with atropin. The cocaine further removes pain and favors the
full eversion of the eyelids.
The instruments required for focal illumination are a biconvex lens of
15 to 20 diopters, and a good oil lamp or movable gas jet. The light of
the sun is not satisfactory. The examination ought to be conducted in a
dark room, or less satisfactorily in semi-darkness. The lamp is held by
an assistant at the level of the eye to be examined, either in front or
behind, or first one and then the other, so that the rays of light may
fall upon the eye obliquely. If the lids are kept closed it may be
necessary to expose the cornea by pressing on the lids with the finger
and thumb. The light is held 8 or 10 inches from the eye and the lens is
interposed between it and the eye and moved nearer and more distant
until the clearest illumination has been obtained of the point to be
examined. In this way every accessible part of the eye may be examined
in turn. The examiner may make his results more satisfactory by
observing the illuminated surface through a lens magnifying three or
four diameters. It is important to observe that the eye of the operator
must be in the direct line of reflection of the pencil of light.
=Cornea.= By focusing the light in succession over the different parts
of the surface of the cornea, all inflammations, vascularities,
opacities, ulcers, and cicatrices will be shown and their outlines
clearly defined. By illuminating the deeper layers of the cornea proper,
the lesions of keratitis, opacities, ulcers and cicatrices will be
shown. To complete the examination of the cornea the light should be
focused upon the iris so that it may be reflected back through the
cornea. This will reveal the most minute blood-vessels, any cell
concretions on Descemet’s membrane, or any foreign body in the cornea
which may have been overlooked.
=Aqueous Humor.= Unless the cornea is densely opaque, the anterior
chamber can be satisfactorily explored by the oblique focal
illumination. The cloudiness or milkiness of iritis or choroiditis
furnishes a strong reflection from its free particles of floating
matter, its blood and pus globules, and its flocculi of fibrine. The
latter have usually a whitish reflection, the blood elements a red
(hypohæma), and the pus a yellow (hypopion). The writhing movements of a
filaria scarcely need this mode of diagnosis. Sometimes, and especially
in the horse, detached flocculi of black pigment are found floating free
in the aqueous and are highly characteristic.
By this illumination one can easily determine the distance of the cornea
from the iris and lens (depth of anterior chamber) which is lessened by
the forward displacement of iris and lens in undue tension in the
vitreous (glaucoma, retinitis, tumors, bladderworms), or of the iris
alone, in irido-choroiditis with accumulation of exudate in the
posterior chamber of the aqueous. The depth of the anterior chamber may
increase in cases of luxation or absence of the lens or softening and
atrophy of the vitreous.
The adhesion of the iris to the back of the cornea may be satisfactorily
demonstrated by focal illumination.
=Iris.= The lesions of the iris are exceedingly common in connection
with recurring ophthalmia in the horse, and examinations in the
intervals between attacks are of the greatest importance. The eye should
be examined as already stated, at a window or door, and if available by
the aid of a mirror. Any changes in form or color, or luster should be
carefully noted, any tension of the eyeball, or angularity of the upper
lid, and any slight blue opacity round the margin of the cornea. Then
the prompt or tardy response of iris and pupil to light and darkness
must be made out. To complete the test the eye should be treated with
homatropin for three-quarters of an hour and with cocaine for ten or
fifteen minutes, and then subjected to oblique focal illumination.
With partial posterior synechia the rest of the pupil is found dilated
while the attached portion extends inward remaining fixed to the capsule
of the lens. If the synechia is complete no dilatation whatever has
occurred. The edges of the adherent iris extend inward as adherent
projections, and any exposed portion of the lens is likely to show black
points, the seat of previous adhesions that have been broken up. In such
cases the periphery of the iris bulges forward from the accumulation
behind it of aqueous humor or inflammatory exudate which cannot escape.
The discoloration of the iris as the result of inflammation, stands out
more definitely under the fuller illumination.
=Crystalline lens.= In exploring the crystalline lens or its capsule for
opacities (cataracts) oblique focal illumination can be employed to the
very best advantage, if the pupil has first been widely dilated by
homatropine and cocaine. The light is concentrated on all parts of the
anterior capsule in turn, then in succession on the different layers of
the lens at all points and finally on the posterior capsule. The
striking reflection from any points of opacity whether pigmentary, gray
or pearly white is diagnostic, not only of cataract, but of its exact
position—anterior or posterior, capsular or lenticular.
=Purkinje-Sanson images.= If the flame of a candle is passed in front of
the eye, at a suitable distance, in a darkened room, and the observer
looks into the eye obliquely from the opposite side, he observes three
images of the flame, reflected respectively from the front of the
cornea, from the anterior surface of the lens and from the back of the
lens. The image from the cornea is erect, bright and clearly defined:
that from the front of the lens is still erect, but larger and dimmer,
because the difference between the index of refraction of the aqueous
and lens is very slight: the third image, which is smaller and clearer
than the last, is inverted, because the surface of reflection on the
back of the lens acts as a concave mirror. The beginner may at first
find it difficult to make out the image from the front of the lens but
with a little care he can do so, and then by moving the light he should
cause each image to pass over all parts of the reflecting surface in
turn. Any unevenness or opacity at any point of the reflecting surface,
will cause the image reflected from it to become blurred or diffused as
it passes over it and thus, not the existence only, but the exact seat
of such opacity is easily demonstrated. Opacities on the cornea cause
blurring of the bright, erect image of the flame as it passes over that
part: opacities on the anterior capsule of the lens blur the dim, erect
image when passed over them: finally, opacities in the body of the lens
or on its posterior capsule, blur the small inverted image as it passes
over them.
Add to this method the oblique focal illumination and the images of the
flame reflected from the three mirror surfaces (cornea, anterior and
posterior lens surfaces) are made much clearer and more distinct than in
any other way. To do this effectively the convex lens should be held so
as to focus the flame in the air nearly in front of the cornea. The
Purkinje-Sanson images are made very definite and clear. If the lens is
approached nearer to the eye so as to throw the image of the flame
within or behind the lens, a gray phosphorescent streak of light is seen
in the depth of the pupil. This is due to the laminated structure of the
lens as well as to the fact that the lens itself is not perfectly
transparent even in its normal condition. The absence of the lens or its
dislocation and displacement downward, below the line of vision may be
inferred from the absence of this gray luminous reflection under this
test.