CATARACT. OPACITY OF THE LENS OR ITS CAPSULE.
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.