Primary Glaucoma in the Dandie Dinmont Terrier
Primary glaucoma is an inherited disease of the eye in which the internal fluid pressure rises above normal. The high pressure destroys retinal and optic nerve tissues to render the eye blind. In acute onset disease there is considerable pain, but in the slower types of the disease the only signs are those of gradual loss of sight and globe enlargement.
In the Dandie Dinmont Terrier it is a slower type of disease that affects the late middle-aged and elderly dog. Sadly the cause is not known and our studies would suggest that it is the sum of several abnormalities that results in the disease.
All are abnormalities associated with that part of the eye known as the drainage or iridocorneal angle (DA). Pectinate ligament dysplasia (PLD) is one of those abnormalities and it is this we look for when gonioscopy is completed. We also look for a narrowing of the DA, but the cause for the narrowing and the eventual closure of this structure is not known. That it happens is certain, but the changes at microscopic level that effect closure cannot be seen in a clinical examination of the eye.
It will take histological studies to provide the necessary details, but, it must be remembered that the changes themselves may be destroyed by the glaucomatous process. Other cellular changes may occur deep within the DA, but again these are not visible to the ophthalmoscope and not seen at gonioscopy. Here again histology will be necessary to describe these possible changes. Primary Glaucoma in the Dandie Dinmont Terrier may be the sum of these three factors, but any certainty of this does not exist.
At the moment, the gonioscopic work we are doing will give information on PLD and DA, but, as said earlier, histololgy will prove necessary to complete the jigsaw puzzle. We need to know about the disease in order to provide effective treatment and those same facts may eventually lead to a DNA based diagnostic test. Little fact at the moment and a lot of new hypothesis.
What can you do as a responsible owner or breeder? Really only one thing - Gonioscopy. I am suggesting currently that 3 gonioscopic examinations should be completed during the lifetime of the dog :
1. In the young dog - 2 - 4 years of age
2. In the middle aged dog - 6 - 7 years of age
3. In the elderly dog - 9 -10 years of age
The early examination will pick up PLD and the later examinations will reveal subsequent possible narrowing and closure of the DA. We have made a good start thanks to the tireless work of several committed breeders, but we need all the support possible if we are to get to the bottom of this particularly nasty disease.
Professor Peter G C Bedford, BVetMed, PhD, FRCVS, DVOphthal, ILTM.
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