by John S. Sleasman, DVM
Tally-Ho: May/June 1975
Glaucoma, by definition, is an increase in pressure within the eye. Glaucoma, or ocular hypertension, may be a result of excessive fluid production or inadequate drainage of fluid from the inner eye. This ocular disease is categorized as primary or secondary glaucoma. Primary glaucoma is considered to be that condition that cannot be attributed to any definite lesion within the eye. Secondary glaucoma arises from specific eye disease.
Certain parts of the eye are particularly important in understanding glaucoma. These structures are in the anterior segment of the eye, and include the iris and ciliary body, the anterior and posterior chambers, the filtration angle, and the intrascleral drainage plexus. The iris (the pigmented tissue surrounding the pupil) divides the fluid cavity of the eye into an anterior and posterior chamber. The ciliary body located where the iris attaches, secretes aqueous humor or the inner fluid of the rye. This fluid fills the anterior and posterior chambers of the eye and drains through the titration angle, past the Pectinate Ligaments (Trabecula) into a series of vessels called the Intrascleral Plexus. It is the Pectinate Ligaments (Trabecula) that are important in basset hound glaucoma. Excessive thickening of these ligaments blocks the drainage of fluid from the eye which leads to glaucoma.
Causes of glaucoma can be genetic or acquired, such as infections or trauma, and some may be a combination of genetic predisposition and a concurrent acquired eye disease. I believe adult basset hounds that develop glaucoma have a genetic defect in the filtration angle and when injury or inflammation occurs in the eye, the marginal drainage in existence is further embarrassed, resulting in an inability of the fluid to drain from the eye.
There are many general characteristics of glaucoma, all of which are not usually exhibited in any one animal. A great deal depends upon the nature of the attack, whether it falls into primary or secondary classification, and length of time glaucoma is present before detection. The general characteristics include: (1) increase in intraocular pressure; (2) pain: (3) cloudy or "steamy" surface of the eye; (4) insensitive surface of the cornea: (5) narrowed distance between cornea and iris; (6) dilated pupil; (7) enlargement of the eye; (8) loss of vision, complete or partial, due to damage to nerve tissue in the back of the eye; (9) corneal changes due to exposure and drying of the cornea.
The diagnosis of glaucoma as established by evaluating the clinical signs described and measuring the inner pressure of the eye. The pressure is determined by the use of an instrument called a tonometer. There are several different tonometers but all basically measure how far the cornea indents when a certain weight is placed on the surface of the eye. The diagnosis of glaucoma can be difficult because other eye conditions can mimic several of the signs of glaucoma.
The treatments for glaucoma are as varied as the causes. The treatment must be tailored to the type of glaucoma. The means of treating glaucoma are medical and surgical approaches or a combination of both. It has been my experience that the medical approach to glaucoma is seldom satisfactory. Most owners are reluctant to assume the responsibility of daily care and observation necessary over the life of the animal. Drugs usually fail to prevent blindness. Because of this, I usually prefer a surgical approach in nearly all cases of glaucoma. In some cases drugs are used presurgically to reduce the pressure and in others to help control pressure post-surgically. Many animals progressively lose their vision regardless of treatment. In many cases, the treatment can be considered a success if the eye is painless and need not be removed. For the above reasons and because of the genetic implications of glaucoma, a diagnosis must be established early in the course of the disease and those animals treated and eliminated from breeding programs.
Studies indicate glaucoma in the basset may be a primary glaucoma due to genetic factors. Some investigators feel that luxated or "slipped" lenses are the cause of the glaucoma because many bassets with the disease have luxated lens. I believe the luxated lens is secondary to the glaucoma.
I agree with the group of investigators who believe the cause of glaucoma in the basset hound is due to a congenital, hereditary defect in the angle of the eye. This defect consists of a sheet of tissue in the angle that decreases the flow of fluid out of the eye. This sheet of tissue is complete in some areas of the circumference of the eye and in other areas has "flow holes" present. Some basset hounds have only a trace of this tissue and others have almost no areas for fluids to flow out of the eye. There are some bassets that show no evidence of this tissue. The finding of abnormal angles in closely related dogs with glaucoma indicates possible genetic factors. In a survey I was involved with, several basset hounds were examined. A high percentage showed varying degrees of abnormal angle development.
Unfortunately, the elimination of glaucoma in the basset hound will be difficult at best. The apparent recessive nature of the disease is likely to cause the incidence of glaucoma in the basset hound to increase. These are a few suggestions that may help to control this disease: (1) be certain any basset hound with an eye problem is examined by a veterinarian (2) if a significant number of cases of glaucoma are detected in a kennel, a veterinary ophthalmologist should be consulted. He will be able to examine the filtration angle of breeding animals and possibly make suggestions concerning future breedings. Glaucoma in the basset hound can only be understood and controlled by cooperation between breeders and researchers.