Chapter 9 Glaucoma
Glaucoma, a disease that affects the optic nerve, is characterized by the death of ganglion cells and is associated with a pathologic elevation of the intraocular pressure. Little doubt exists that some of the clinical signs of the disease (e.g., corneal edema and posterior cupping of the optic nerve) are directly related to the increased pressure in the eye. The cause of the elevated pressure is poorly understood in many cases. A reduction of the outflow of aqueous humor from the eye in the face of continued secretion appears to be involved. It is presumed that the major obstruction to aqueous outflow from the eye is the result of either an anatomic or a physiologic abnormality in the outflow mechanism through the iridocorneal angle—the site of the bulk of the aqueous drainage in most mammalian species. Glaucoma can be a primary (and eventually bilateral) inherited disease (certainly the case in dogs), or it can develop secondarily to other ocular conditions in which the flow of aqueous in the eye is impeded or the outflow pathways are obstructed. Obstruction may occur if the lens is abnormally positioned (lens luxation) and when cells or inflammatory debris blocks the drainage angle (as is the case with uveitis, neoplasia, and hemorrhage). Many cases of glaucoma in cats are associated with uveitis. Glaucoma is often a painful, blinding disease in small animals. It is essential that the clinical features of glaucoma are recognized, because therapy for other causes of a red, painful eye may be contraindicated in patients with glaucoma. Only in cases in which the diagnosis is made and treatment started early does any hope exist that the disease may be controlled even remotely for any length of time.