Text book of veterinary medicine, Volume 3 (of 5)

by James Law

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.