Symptoms. The tension of the eye ball is excessive as ascertained by pressure of the finger, or by the spring tonometer. If the increase of tension has come on suddenly, the cornea is somewhat cloudy, and less sensitive to the touch. If one eye only is attacked the contrast between the two is very marked and diagnostic. The anterior chamber is diminished in size by the projection forward of the iris and lens. The iris is usually contracted so as to show a dilated pupil reflecting a smoky, grayish green or yellowish green hue. The iris is either irresponsive to light or responds very slowly and imperfectly. With the ophthalmoscope the most marked features are the “cupping” or depression of the optic disc by pressure, and the pulsations in the retinal arteries. These pulsations are especially easily seen at the margin of the depression which represents the seat of the lamina cribrosa and the point of entrance of the optic nerve. They are rendered even more manifest by pressure on the eye. They are due to the prompt emptying of the blood vessels by the intraocular pressure, so that these are only momentarily filled at each cardiac systole.
Ophthalmologists recognize three varieties of glaucoma: acute inflammatory glaucoma, simple glaucoma without apparent inflammation, and secondary glaucoma, the result of another disease.
Acute inflammatory glaucoma is the one condition in which, in the absence of a midriatic, inflammation is associated with dilated pupil. It is liable to occur in a series of attacks, which increase in severity, hence its supposed identity with recurrent ophthalmia in the horse. The entire group of symptoms have, however, been rarely or never seen in the horse. They are distinctly more common in dogs.
Simple glaucoma comes on more slowly, becomes chronic and is to be recognized by the physical symptoms in the absence of inflammation, notably by tension of the bulb, diminution of the anterior chamber and cupping of the optic disc.
Secondary glaucoma is the direct result of some other disease of the eye:
Complete posterior synechia acts by confining the liquid which is secreted, to the posterior chamber whence it finds no ready outlet through the pupil, and causes a marked bulging forward of the iris and tension of the eyeball.
Slighter anterior synechia in the form of cicatricial adhesions between iris and cornea in the sclero-corneal margin, acts by blocking the principal drainage canal of the aqueous humor, which lies in this angle.
Traumatic injuries implicating the capsule of the lens and admitting the aqueous humor freely to the lens substance determines softening, swelling and so much irritation as to increase the secretion largely and determine intraocular tension.
The same may result from luxation of the lens and irritation of the ciliary circle by dragging.
Other causes are disease (atheroma) of the retinal vessels and the growth of tumors in the interior of the eye.