The cornea is the clear, tough, elastic membrane that covers the front of the eyeball. It is lubricated by the secretions of the tear glands which are vital to the health of the structure.
Occasionally in older animals the secretions of tears may become interrupted, causing the surface of the cornea to dry out and become susceptible to infection.
If the secretion of the tear glands cannot be restored, the pet owner must regularly bathe the eye with a saline solution and apply drops that simulate the composition of tears.
Injuries to the cornea are extremely painful and potentially very serious. Sharp foreign bodies, cat scratches and air-rifle pellets are common causes of corneal injury.
The first reaction of the dog is to keep the eyelids tightly closed, and it resents any handling. Very often it is necessary to anesthetize the animal to properly examine the cornea. Deep punctures or tears allow the fluid in the front of the eye to escape and the eye may appear markedly smaller than normal.
If the injury to the eye has been present for some time, the blood vessels supplying the cornea dilate and flood the structure with white blood cells, making the cornea opaque. Large wounds have to be sutured.
Fortunately, the profuse blood supply ensures that healing proceeds quickly, and once the wound is made watertight, the fluid in the front of the eye is restored and the eye assumes its normal shape.
Infections of the cornea occur commonly in some breeds of dogs. Pekingese, pugs, boxers, King Charles spaniels and chihuahuas all have very large, prominent eyes which are more susceptible to injury and infection.
Any inflammation of the cornea, whether it be a result by some irritant chemical, or by sharp foreign bodies or infection, first causes the structure to become cloudy.
In severe infections the cells on the surface of the cornea may be destroyed and a crater forms in the otherwise smooth surface of the cornea. This is a serious condition and must be treated urgently.
Treatment may involve suturing the third eyelid over the damaged area and suturing the eyelids together to immobilize the structures and give them a chance to heal. Of course, antibodies are administered both to the eye itself and internally.
Diseases of the lens of the dog are common. Opacity of the lens, or cataracts, are most obvious and it occurs frequently in old animals.
The first sign of changes in the composition of the lens is seen as a cloudiness or bluish discoloration. At this stage the dog may show impairment of vision only at night or begin to lose its ability to catch balls or judge moving objects.
Later, as the opacity becomes greater and as less light is admitted into the back of the eye, the dog may begin to bump into furniture or stumble when going down stairs.
Treatment of cataract is by surgically removing the affected lens. The operation is technically quite simple; unfortunately not all dogs regain their sight after such an operation as there is often associated degeneration of the retinal tissues at the back of the eye.
Before deciding on surgery, an opinion from a veterinarian specializing in ophthalmology should be obtained. This can be arranged through your own veterinary surgeon.