GLAUCOMA IN THE ENGLISH SPRINGER SPANIEL
WHAT IS GLAUCOMA?
Glaucoma is increased pressure within the eye. Cells inside the eye produce a clear fluid ("aqueous humor") that maintains the shape of the eye and nourishes the tissues inside the eye. The balance of fluid production and drainage is responsible for maintaining normal pressure within the eye. In glaucoma the drain becomes clogged but the eye keeps producing fluid. Therefore, the pressure in the eye increases, and this can actually cause the eye to stretch and enlarge.
WHAT CAUSES GLAUCOMA?
Glaucoma is classified as either "Primary" or "Secondary".
- Primary Glaucoma is an inherited condition. It occurs in many breeds including the English Springer Spaniel. It usually begins in one eye, but almost always eventually involves both eyes, leading to complete blindness. Increased pressure within the eye is caused by abnormal drainage of fluid through the iridocorneal angle (the angle at which the iris and cornea join).
- Secondary Glaucoma occurs when other eye diseases cause decreased fluid drainage. Common causes of secondary glaucoma are inflammation inside the eye (uveitis), advanced cataracts, cancer in the eye, lens subluxation or luxation (partial or total lens dislocation), and chronic retinal detachment.
HOW IS GLAUCOMA DIAGNOSED?
Determining if your dog has primary or secondary glaucoma is important because the treatment needed and the prognosis for vision is different for each type.
Glaucoma is one of the conditions your Vet might suspect if your dog has a painful eye. The diagnosis can be confirmed by measuring the pressure inside the eye using a tonometer.
Veterinary Ophthalmologists use Gonioscopy to determine whether the glaucoma in an affected dog is primary and/or for screening purposes to determine (before the onset of any symptoms) how predisposed the eyes are to developing primary glaucoma. This test involves placing a special contact lens directly onto the surface of the eye which allows examination of the drainage angle. Gonioscopy is a one-off test, and screening can be carried out on dogs from the age of 4 months onwards.
HOW DOES GLAUCOMA AFFECT THE EYE?
- Vision Loss. Pressure damage to the optic nerve and decreased blood flow to the retina results in loss of vision. However, if the pressure in the eye remains uncontrolled, the retina degenerates and vision is permanently lost. Permanent blindness can occur within hours if the pressure is very high and the glaucoma develops rapidly.
- Pain. Increased pressure inside the eye is painful. The pain persists in the form of a constant headache or migraine. This discomfort can result in decreased activity, less desire to play, irritability or decreased appetite, and is often not apparent to the owner.The eye may be red and the dog may paw at it or rub his/her head along the carpet. The eye may look cloudy due to swelling of the cornea and the dog will be very sensitive to light. The affected eye may seem larger, or appear to bulge out, relative to the other eye.
- Remember - your dog will not tell you the eye is uncomfortable!
HOW IS GLAUCOMA TREATED?
Glaucoma is an emergency!
- Medical Therapy. Since glaucoma occurs because fluid is not draining from the eye fast enough, the logical treatment is to open up the drain. Unfortunately, opening the drain and keeping it open is difficult. There are many different types of eye drops and pills which are aimed at decreasing fluid production by the eye or increasing fluid drainage from the eye. While these medications are helpful, they usually do not control glaucoma in the long term. Consequently, they are used mostly to help prevent or delay the onset of glaucoma in the remaining visual eye, and as temporary treatment until surgery can be performed on the affected eye.
- Surgical Therapy. The type of surgical procedures available for glaucoma depends upon whether the eye still has the potential for vision. For visual eyes, the pressure can be reduced by implanting a drainage tube into the eye. For permanently blind eyes, the eye can be removed.
Which procedure is best for your dog depends on the type of glaucoma, the potential for vision, and your preference for the cosmetic appearance of your dog's face. Glaucoma is a frustrating disease because it requires constant monitoring, may require several different therapies, has a high cost financially, and despite excellent care, often still results in permanent vision loss.
The key to preserving vision is early detection.
Primary Glaucoma with Reference to the English Springer Spaniel
P.G.C. Bedford BVetMed PhD DVOphthal DipECVO FRCVS
You should have no doubts about the fact that the type of Primary Glaucoma which occurs in the English Springer Spaniel is the most devastating eye disease the middle-aged dog could suffer. It is known as angle closure glaucoma and it is characterised by sudden onset blindness and pain, both of which prove so very difficult to treat that a life without sight is the usual prognosis for the patient. Such is the pain and the damage to the eye that the removal of the eye may prove necessary in many instances.
It is a disease to be avoided at all costs, but sadly the type of inheritance involved is unknown. This always renders breeding advice difficult, for such advice cannot be specific enough for ease of selection of the right genotype and will make the future development of a DNA based test really difficult.
Fortunately, although not 100% reliable, a relatively simple clinical diagnostic test is available to give guidance in breeding programmes. The test is called Gonioscopy - it allows the identification of those dogs which may be predisposed to Glaucoma. In the English Springer Spaniel a once only examination is all that is required. This can be done from 4 months of age onwards.
But let me begin at the start of the story:
The eye contains a fluid called the aqueous which serves the same purpose as a blood supply to the cornea and the lens. As such there is a circulation of this fluid inside the eye: aqueous is produced from blood by structures known as the ciliary processes and once it has circulated inside the eye to provide oxygen and glucose to the cornea and lens it is taken back into the blood stream within a part of the eye known as the ciliary body. Angle closure glaucoma is due to the obstruction of aqueous uptake by the ciliary body. The ciliary body contains a space, the ciliary cleft, which extends around the 360 degrees of the eye into which the aqueous passes to move back into the blood vessels. In angle closure glaucoma, the ciliary cleft closes within a matter of a few seconds and, because the aqueous cannot escape the eye but its production continues, the fluid pressure inside the eye rises to double or treble its normal value. This causes pain and the increased pressure destroys cells within the retina so quickly that often treatment is started too late to restore eyesight.
So, the mechanism involved in English Springer Spaniel Primary Glaucoma is the closure of the ciliary cleft (the space) within the ciliary body. Gonioscopy allows the examination of the entrance to the ciliary cleft. In the normal dog the entrance is wide open (2mm), but in glaucoma predisposed dogs the entrance is narrowed as the result of what is called pectinate ligament dysplasia (PLD). In normality the entrance to the ciliary cleft is spanned by strands or fibres of a structure referred to as the pectinate ligament (the Latin word "pecten" means comb- like), so this ligament has the appearance of a long comb whose teeth are 2mm long. In PLD the teeth do not form properly and the entrance to the ciliary cleft is narrowed and partially occluded (blocked) as a result. It is this narrow entrance which suddenly closes to deny aqueous outflow in angle closure glaucoma.
Why the "angle" in the terms "narrow angle" and "angle closure"? Well, the entrance to the ciliary cleft lies at the angle formed by the cornea and the iris.
Predisposed dogs are born with narrowed angles as a result of PLD and it is the narrow angle which closes to give rise to angle closure glaucoma. (The word "primary" simply means inherited). Gonioscopy will identify the predisposed dog before the disease occurs. However, the exact mechanism involved in the closure of a narrowed angle is not totally understood, but what is universally accepted is that PLD is the marker for angle closure. Thus gonioscopy is such a useful examination to be used in the assessment of breeding animals. It is far preferable to avoid Primary Glaucoma through safe breeding than to produce predisposed and glaucomatous animals, because treatment is so very difficult.
I have already said that by the time veterinary assistance is sought it is too late to save the retinal cells, but even if that treatment is instituted early enough all that can be done is to slow down the speed of the progression of blindness. The good news is that there is evidence to suggest that glaucoma treatment started in predisposed dogs before glaucoma occurs can be invaluable in preventing or delaying the onset of the disease.
Thus, I cannot advocate the value of gonioscopy enough - it allows the identification of predisposed dogs, stops their use in breeding programmes and alerts the clinician to the use of prophylactic treatment.
The incidence of primary angle closure glaucoma in the English Springer Spaniel is not known, but it is low. Routine gonioscopy should prevent the problem becoming commonplace.
I would encourage you to keep up with clinical examinations for PRA, MRD and Primary Glaucoma to help you breed healthy stock.
Professor Peter G C Bedford