Definition. Forms: lenticular, capsular, cortical, nuclear, polar,
black, diabetic, traumatic, immature, mature, senile. Causes: impaired
nutrition of lens, inflammation of iris, choroid, ciliary body,
retina; recurrent ophthalmia. Proliferation of cells. Increased
density, chemical changes, degenerations. Sugar, sodium chloride,
naphthalin. Rachitis. Senile. Blood pigment. Symptoms: shrunken bulb,
opalescent zone around cornea, angle on upper lid, shying, extra ear
activity, high stepping, better sight in twilight, homatropia,
examination facing the light, Purkinje’s images, ophthalmoscopic
examination. Prognosis hopeless. Treatment: phosphureted oil, massage,
operation in horses, discission, under antiseptic precautions,
extraction under careful antisepsis, suction.
_Definition._ Any pathological change in the lens or its capsule
diminishing its transparency.
_Varieties._ The opacity may be situated either in the lens
(=lenticular=) or in its capsule (=capsular=). Again, it may be in the
outer part (=cortical=) or in the central part (=nuclear=) of the lens.
If the opacity is on the capsule in front of the lens it is =anterior
capsular=; if on the portion behind the lens it is =posterior capsular=.
If the opacity is caused by black iris pigment adherent to the capsule
it has been called =black cataract=. If the lenticular cataract is small
and round, it is =polar=, and it may be =anterior= or =posterior polar=
according as it is situated near the front or back of the lens.
=Diabetic cataract= is one associated with mellituria. A =traumatic
cataract= is one resulting from a wound of the lens which admits the
aqueous humor and causes softening, swelling and finally solution of the
substance of the lens. The =immature= or =unripe cataract= is one in
which the lens is not yet wholly involved and indurated; the =mature= or
=ripe=, when such consolidation has extended throughout. =Senile
Cataract= is seen in old horses, dogs, cats, birds and very
exceptionally in cows. This usually attacks both eyes at once. A
degeneration takes place in the fibres of the lens, which are invaded by
sclerosis beginning at the centre of the organ.
_Causes._ In domestic animals cataracts are commonly the result of
impairment of the nutrition of the lens in connection with inflammation
of the iris, choroid, ciliary body, retina, or hyaloid membrane, and
above all, in solipeds, in recurrent ophthalmia. It may be assumed that
a transparent tissue composed of cells can only maintain its
translucency so long as the most perfect equilibrium is maintained as
regards the mutual relation of the cells, the pressure of its
interstitial plasma, and the chemical composition of both plasma and
cell structures. The slightest deviation in any direction will impair or
abolish the transparency of the tissue. In inflammation this occurs in
various ways, through the increased cell multiplication and the change
in the nature of the cells, through the increased exudation and the
alteration of the solid parts as regards compression and relative
position, and through chemical changes in the exudate which contains
more salts, fibrinogenous material, etc., than the normal plasma. The
same is true of all the post inflammatory degenerative processes that
take place in the lens.
The formation of cataract from chemical alteration in the fluids is
familiar in diabetic subjects,—man or beast (Altenhof). It can be
produced experimentally in frogs by injecting sugar, common salt or any
other readily diffusible saline solution under the skin (Kunde). Rabbits
that are fed naphthalin develop cataract which radiates in lines and
streaks from the pole towards the periphery and in the cortical portion
of the lens. Perhaps the lamellar cataract of rachitic patients is also
to be attributed to the lack of earthy salts in the plasma of the lens.
_Senile cataract_ may be hypothetically attributed to impaired
nutrition, degeneration in the lens or its capsule, or less commonly to
disease of the blood vessels of the eye, or gradual changes in the
plasma. It occurs in horse, ox or dog at ten years old and upward.
=Anterior Capsular Cataract= sometimes results from the deposition of
=blood pigment on the capsule= in cases of extravasation into the
anterior chamber. This is closely allied to the black or spurious
cataract which consists in the adhesion of the uveal pigment to the
capsule, and its detachment from the iris.
Kunde who caused cataract in frogs by injection, subcutem or ingestion
of concentrated solutions of sugar or salt, attributes the result to the
sudden abstraction of water from the crystalline lens. Even the cell
multiplication in inflammatory cases, he holds to favor this, since the
new cells having little vitality are especially subject to granular and
other deposits and degenerations, with loss of water or of transparency.
_Symptoms and diagnosis._ The examiner should apprehend cataract after
internal ophthalmia. Much more so, if there is apparent diminution of
the bulb, an opalescent zone around the outer border of the cornea, or a
marked angle in the curvature of the upper eyelid, as usually occurs in
recurrent ophthalmia. When a horse suddenly acquires a habit of shying,
of starting back or to one side when approached, when confronted with
strange or unexpected objects, or with deep shadows like those from
electric lights, he is to be suspected. When he carries his ears in an
unusually alert manner, turning one forward and the other back, when he
steps higher than before to avoid unseen objects, suspicion should
attach to him. If he sees better in twilight than in the full sunlight,
central cataract may be feared, while the periphery which is exposed by
the dilatation of the pupil in semi-darkness is still clear. In all
examinations for soundness, the greatest care should be taken to exclude
the possibility of overlooking an existing cataract.
In the very early stages, while internal inflammation and photophobia
are still present, the pupil may be contracted so that lesion can easily
escape notice. Any contraction of the pupil therefore disproportionately
to the light, should demand a careful examination with the pupil dilated
in darkness or by the action of atropia or homatropin. In the more
advanced cases with no persistent inflammation and an advanced opacity
of the lens, sensitiveness to light is greatly lessened, the pupil is
dilated and the cataract is easily detected.
In cases approximating to the condition last named it is usually only
necessary to place the animal in a sombre or dark building, with his
head facing the light at an open door, or window and best with full
sunlight. Let this fall full upon the eye, and let the observer view the
pupil diagonally from each side when any opacity may be detected.
When the pupil is too narrow, several drops of a one per cent. solution
of atropia sulphate may be dropped within the lower lid and left for ten
minutes until the pupil is widely dilated. Then the examination may be
made as above, or still better the animal may be taken into a dark
chamber and examined by one of the following methods:
A light, preferably a candle, is placed in front of the eye and moved
from side to side, upward and downward, so as to bring its images over
all parts of the cornea and lens. In the normal eye there are reflected
three images of the light, one large, clear, and upright from the
anterior surface of the cornea, one, much smaller but still upright,
from the anterior capsule of the lens, and one, small and inverted, from
the posterior surface of the lens and capsule. Any opacity in the lens
or on its posterior capsule, will cause the posterior (inverted) image
to become indistinct, and as it were a diffuse white blur, as it passes
over that spot. The other small (erect) image may be even clearer than
normal in passing over the opaque area because of the mirror-like
reflecting action of the white cloud behind it. The movement of the
light so as to pass its image over all parts of its surface in
succession will certainly reveal the existence and seat of the cataract,
by the blurring of the inverted image of the flame.
Another method is by oblique illumination, the patient’s head being
turned away from the light and the interior of the eye being lighted up
by reflection from a mirror. If the pupil has been sufficiently dilated
all parts of the lens can be scrutinized in this way and the slightest
opacity detected by the grayish or whitish haze.
If there is still doubt as to the nature of such appearances, it may be
set at rest by illuminating the depth of the eye with the ophthalmoscope
when the opacities will appear as dark areas in the general red ground.
(See Systematic Examination of the Eye.)
The _prognosis_ of cataract is almost invariably hopeless. I have seen
newly formed opacities of the capsule clear up in a day or two, and such
recovery in very slight traumatic injury and superficial exudation is
recognized as possible, but a slowly forming cataract is usually there
to stay. Those that clear are presumably only exudates on the capsule
and not true cataracts.
_Treatment._ While exudates on the capsule may disappear under a course
of purgatives and diuretics, practically nothing is to be expected from
medical treatment in true cataract. The instillation of phosphorated oil
(1–2 per cent.) daily into the conjunctival sac as formerly recommended,
may be helpful in some of the superficially opaque membranes, but for
formed cataract it has proved useless. Massage with, or without
ointments can temporarily lessen ocular tension and reduce the liquids
in the zonula of Zinn, and canal of Schlemm, but it is only in very
exceptional recent cases, in which it has given permanent benefit, and
even these were probably spurious cataracts.
The question then is essentially whether we should operate or not. In
the =horse= the objections to operation are almost conclusive in all
cases. The eye in which the lens has been depressed or extracted can
never see objects clearly without the aid of biconvex glasses, and it is
impossible to fit these to the animal. The horse that is blind can go to
pasture or be driven in harness with safety, but the one that sees all
objects distorted or blurred is liable to become a shyer endangering the
life of his rider or driver. The greater number of cataracts in horses
come from recurrent ophthalmia and are associated with opacity of the
vitreous, detachment of the retina, exudates in the choroid,
degeneration of the optic nerve, or other lesion which of itself would
destroy vision. Almost the only object of removal of the lens in such
cases would be to make an unsound horse pass for a sound one. Even this
is usually unattainable because the thickened capsule remains as a dense
white cloud or the opacity of the vitreous shines through the pupil. In
dogs the cataract is usually associated with fewer complications, and
the resulting imperfect vision is not a source of danger to man.
Extraction of the opaque lens may in this case appeal so strongly to the
sense of comfort of the owner that the operation may become permissible
or desirable.
In man the operation may have to be delayed for a considerable time
because of the unripeness of the cataract. The center of the lens may be
firm and opaque while the outer layers are so soft that they would be
likely to be retained in the capsule and would not only produce
persistent opacity, but would be a continual threat of destruction of
the eye by active inflammation. The ripeness is ascertained by careful
scrutiny of the shadow of the iris during illumination of the interior
of the eye. If ripe, the dark shadow of the iris approximates closely to
the margin of the iris itself, whereas if the outer portion is unripe
there is a clear zone of greater or less depth between the margin of the
iris and the shadow reflected by the opaque portion of the lens.
In the lower animals the question is less important as we do not aim at
securing perfect vision, and the danger of inflammation is therefore the
main consideration. Escaping this, the aqueous humor may be expected to
dissolve and remove the greater part of the still adherent lens
substance, and the unsightliness of the dense white cataract is largely
done away with.
=Discission.= Tearing of the capsule so as to admit the aqueous humor to
the lens may be admissible in the =young= with =soft cataract=. The
liquid causes gradual swelling up, solution and absorption of the lens
so that in the course of a week or two the whole may be removed. It is
not, however, unattended by danger, as the rapid swelling of the lens
will sometimes determine an inflammation which will lead to complete
destruction of the eye. The eye is first thoroughly washed with aseptic
cotton and a sublimate solution (1 ∶ 1000), and is then rendered
anæsthetic by cocaine (5 to 10 per cent. solution) or in the large
animals general anæsthesia is produced by ether or chloroform. The
eyelids are held apart by the lid speculum, the nictitans held if
necessary by forceps, and the bulb steadied by seizing it with hooked
forceps. A cataract needle is passed through the cornea close to its
border, and carried through the pupil, previously dilated with atropia,
so as to tear an opening in the anterior capsule about two-thirds the
diameter of the lens. If the toughness of the capsule threatens to
endanger the ciliary body by dragging upon it, two needles or fine hooks
may be introduced through opposite borders of the cornea (inner and
outer) and the capsule may be torn without throwing any strain on
surrounding parts. The pupil must thereafter be kept dilated by atropia
to obviate adhesion of the iris to the wound and the eye must be kept in
comparative darkness and aseptic. If active inflammation sets in, cold,
astringent or iced dressings may be called for, while if the swelling of
the lens is threatening it should be at once extracted. If the eye
becomes unduly tense, puncture of the cornea is indicated, and the
relief of tension will sometimes start a tardy solution into renewed
activity.
=Linear extraction of the lens.= The animal and the eye having been
prepared anæsthetically antiseptically, and midriatically as for
discission, the lids are fixed with a speculum, the nictitans and the
bulb with forceps, a Gräfe cataract knife is introduced through the
inner side of the cornea, close to its margin and with its point
parallel to the front of the iris. The handle is then raised and the
cornea detached from the sclera by a series of gentle sawing motions
until it has reached a point parallel to the outer margin of the cornea.
If the pupil is insufficiently dilated, the iris should now be seized by
forceps drawn out through the corneal wound and snipped off by scissors
curved on the flat. Then the cystotome (hooked knife) is introduced with
its back turned downward and carried to the further side of the capsule
and close to the iris, its cutting point is turned backward and inserted
in the capsule, and drawn across from side to side to make an orifice
large enough for the escape of the lens. It is then given a quarter
revolution so as to turn the point of the knife downward and is
withdrawn from the wound back first. The lower part of the sclera and
cornea is now gently pressed with a lens spoon so as to dislodge the
lens from the capsule and deliver it through the corneal wound. Counter
pressure may be made on the sclera at the upper part of the eye ball.
The cornea is now gently stroked with cotton dipped in sublimate
solution to pass all blood from the anterior chamber, and render the
parts antiseptic. The iris is carefully replaced inside the cornea and
any obstinately protruding parts must be excised. The eye is now covered
with cotton steeped in a sublimate solution (1 ∶ 1000) and bandaged
without undue pressure, and the animal tied to two sides of the stall so
that it is impossible to rub the eye.
It is well to dress the eye on the second day, and if adhesion of the
wound is complete it may be left without bandage at the end of a week or
a fortnight.
Success depends mainly on the avoidance of infection. Therefore every
indication of local or general infection should forbid the operation.
Any existing infectious disease or any local eczema, conjunctivitis or
disease of the lachrymal apparatus should be cured and the region
thoroughly disinfected before proceeding. The head should have a good
soapy wash, followed by a sponging with sublimate solution (1 ∶ 1000),
the conjunctiva carefully washed out with the same and a bandage damp
with it applied over the eye. This bandage is only removed on the
operating table. Cloths dampened with the solution are laid on the face
around the eye, the eye is cocainized with a 5 per cent. solution
applied at intervals of one minute and when quite insensible the
operation is commenced. The greatest care must be taken to render the
hands of operator and assistants and all instruments thoroughly aseptic.
The instruments are taken from a 4 per cent. solution of carbolic acid
and placed in water (which has just been boiled) until needed, and to
wipe the eye or make any application, sterilized cotton only is used and
never touched to the eye more than once. A sublimate bandage is placed
over the eye and worn for ten days or a fortnight. Then if the corneal
incision is healed and pale it may be left off. The pupil should be kept
dilated by a few drops of atropia daily for this length of time.
Any occurrence of iritis or choroiditis usually indicates infection and
must be treated on general principles, but with especial reference to
disinfection, and if this cannot be secured the eye will be almost
inevitably lost.
In case of renewed opacity through thickening of the capsule an aperture
must be torn in that membrane by the same method as in discission. This
is commonly known as needling. It must be conducted under the same
antiseptic precautions as in extraction.
_Suction._ This is only applicable to a lens which has become fluid as
well as opaque. It consists in withdrawing the liquid lens through a
hollow needle.