Understanding Glaucoma & Goniodysgenesis in SWD's.
Updated: Oct 28, 2020
What is Glaucoma and how does it impact Spanish Water Dogs?
Firstly, thank you for taking time out to read this blog. Before we start, we have a small favour to ask. We are currently undertaking a fundraising campaign to research and develop a DNA Test that once and for all will be able to conclusively show whether an SWD has a predisposition to Glaucoma. To get to this point though takes time, money and a lot of research.
Please help by clicking the image on the left and adding your support. Every penny raised goes directly to funding the research and developing the test, which will benefit the future health of all Spanish Water Dogs across the globe.
At the end of the blog we also have further information about an upcoming mass DNA sample collection exercise which we need help with as well.
Please also share this blog across you social media platforms. Raising awareness and understanding of the condition will only lead to improving the future health of the breed.
What is Glaucoma
So just what is Glaucoma? Well it’s a progressive disease that occurs in humans, dogs and many other animals. Whilst medical treatment and surgical procedures are used to delay the final blinding outcome, none of them are curative.
Glaucoma is a disease of the optic nerve (optic neuropathy) that is characterised in dogs by high intraocular pressures, or in layman’s terms, a build-up of pressure inside the eye itself. For dogs that have this condition, both eyes are affected, although there tends to be a delay of onset between the two. But the final outcome is always inevitable and that is complete blindness.
The front chamber of the eye is filled with fluid, known as Aqueous Humour, which helps to maintain sufficient pressure in the eyeball to keep it distended in its spherical shape and is clear to allow light to pass through. Without this fluid being present the eyeball would shrivel up. In a normal eye a part called the ciliary body constantly produces this fluid to maintain the pressure inside the eye. As new fluid is pumped into the eyeball existing fluid is removed through a part called the Iridocorneal Angle (ICA) or simply the drainage angle. This allows fresh fluid to continually circulate through the eye.
In a glaucomatous eye the interaocular fluid is constantly produced and the flow of the fluid out of the eye is impeded. In dogs with primary, hereditary glaucoma, (like the SWD), the tissues of the meshwork inside the drainage angle become thickened, causing the channels to narrow and ultimately become blocked. The drainage angle ceases to function and prevents the fluid from draining. Meanwhile new fluid is still being produced and consequently the pressure inside the eye increases. It is that build-up of pressure that has devastating effects.
Think of it like a water balloon that has a pin hole half way up. As the water flows into the balloon it makes the balloon swell into its oval shape, much like an eyeball. As the pressure of the water builds the balloon expands and the water level increases. It then reaches the pin hole and starts to escape, keeping the balloon swollen in its oval shape but preventing it from overflowing or bursting. The correct constant pressure is maintained. Without the pin hole being present there is nowhere for the water to go, the pressure builds and builds.
Primary glaucoma is the result of an inherited defect leading to dogs that are born with narrow drainage angles. If the dog has inherited normal, wider drainage angles, it is highly unlikely that the dog will go on to develop primary glaucoma later in life. This does not mean to say that they are immune to secondary glaucoma as this is an issue that is not inherited, but is instead due to reasons such as eye injuries, inflammation, and due to other eye conditions such as cataracts. The initial signs of the disease are very often overlooked and frequently mistaken for other problems associated with the eye. Unfortunately they can mimic inflammation or conjunctivitis. The symptoms can include:
• Redness • Cloudiness • Bulging of the eye • Aversion to touch near the eye • Dilated pupils
• Loss of vision
If treatment for glaucoma is not started within a few days or, sometimes, a few hours, the pressure will increase and the dog’s vision will be lost completely from the affected eye. The pressure damages the cells of the retina and the optic nerve and this quickly becomes irreversible. It can also break down the structures holding the lens in place (lens luxation) and cause damage to the iris and cornea.
The pain associated with glaucoma, which is often severe and can cause intense headaches and depression in a dog, is due to the increasing pressure within the eye because of the level of fluid increasing. The eye begins to bulge and becomes discoloured, cloudy and often looks red and sore as seen in the adjacent photo. Glaucoma can occur over a period of time, but may also manifest itself incredibly quickly. It is often usual for one eye to be affected first and the other to soon follow, but it is also found to affect both eyes simultaneously.
The high intraocular pressure caused by glaucoma must be considered as an emergency situation. If not treated quickly, loss of vision may become permanent. If there appears to be a problem with the dog’s eyes, it is imperative that the owner seeks professional advice at the earliest opportunity. If a diagnosis is made, treatment can then begin immediately, or alternatively, a specialist can be contacted and arrangements made to gain more a more reliable result with the use of more sophisticated and comprehensive equipment.
The current testing system
The most common test currently carried out for glaucoma (often recorded as PLA) is known as a Gonioscopy. Under Kennel Club guidelines specifically relating to Spanish Water Dogs, it is a requirement that any dog being considered for use in a breeding programme is tested. This is because Spanish Water Dogs as a breed have a known predisposition to the condition. That’s not to say every Spanish Water Dog will contract it, however it is more prevalent than not within the breed and is therefore essential to understand any possible risks of it being passed on to future generations. The ideal is to breed dogs that have no or little signs of the predisposition in order to help eradicate the condition from the breed altogether. But where this is not possible at least reducing this risk will help to alleviate it. And whilst it is a necessary requirement for breeders, it is highly recommended that all owners consider having their dogs tested so they can at least be alert to any potential risk of their dog developing it. There is some adage in the old saying, forewarned is forearmed.
Right… back to the test! Remember those tissues of the meshwork inside the drainage channel that can become thickened, well these are known as the pectinates ligaments and this is effectively the door of the drainage channel of the eye. A gonioscopy test involves a specialist ophthalmologist conducting an examination of the pectinates ligaments of the iridocorneal angle. It is performed by placing a contact lens over the eye after the application of a topical anaesthetic drop and it lasts for a few minutes.
Up until 2017 a dog would be graded as either affected or unaffected. However since 2017 a new four tier grading system has been introduced to assist in better quantifying the risk to a dog of developing glaucoma based on the measurements of pectinates ligaments. This grading system operates on a scale of 0 to 3 and is best understood by reviewing the images below.
These images show close up the Pectinate Ligament Abnormality (PLA) evaluated through a Gonioscopy examination. The inset magnified images show the close up of the drainage channel in the eye at the different gradings on the new PLA tiered system.
In the top left image marked [a] we can see the Pectinate Ligament fibres in a normal eye that has a grading of 0. The channel is nice and clear which means that the Intraocular fluid will drain away unimpeded.
In the top right image marked [b] we can see a slight thickening of the Ligament fibres which results in this eye being graded 1. Whilst the thickening is present fluid is capable of draining away.
In the bottom left image marked [c] the Pectinate Ligament abnormality is graded 2. There is a heavier thickening of the ligament fibres, but fluid is still capable of passing.
In the bottom right image marked [d] we can see that the ligament abnormality has caused the drainage channel to become blocked, which places the dog at the highest risk of developing Glaucoma, therefore it is graded as a 3.
The following table provided in guidance produced by the British Veterinary Association (BVA) further breaks down the tier scale banding to identify the percentage risks attributed to each grading.
The impact of the results for breeders
As previously mentioned, the purpose of testing is to allow for more informed breeding decisions to be made when considering the advancement of the health of the breed.
Current advice from the BVA and Kennel Club states that “in general it is recommended that dogs affected by known inherited eye conditions should not be bred from. With regard to goniodysgenesis, it is preferable to breed only from dogs graded as 0 or 1. Dogs graded as 2 (moderately affected) have a greater risk of developing and passing on the condition to offspring and any breeding decisions must take other factors into account, such as significant concerns relating to maintenance of genetic diversity and the prevalence of the condition in the breed. The KC advises that in dogs graded as 2, only those in excellent health and with good results from other screening schemes may be used for breeding, taking particular care to use mates with the best possible gonioscopy results (preferably grade 0). Further research may lead to the updating of this advice.”
In an ideal world all SWD’s that are to be mated would be graded 0 under the PLA scheme, which would eventually result in eradicating the risk of developing goniodysgenesis and/or glaucoma out of the breed. Low percentage (say 30%) Grade 2 dogs, may still be considered suitable for breeding if all other health test results and characteristics suggest them to be suitable but this warrants discussion with your opthalmologist and due consideration of all other factors. However it is recognised that the current population of Spanish Water Dogs in the UK is significantly small, especially when comparing them to a lot of the other breeds. This in turn limits the options for potential mates, especially when considering other factors such as inbreeding coefficients. It is therefore important for breeders to carefully consider all factors when making decisions around selecting the right pairings, whilst being mindful that one of the aims to try and strive for is reducing the impact that this disease has within the breed.
SWD Club research into developing a DNA Test for Glaucoma.
At the beginning of this blog we put out a plea for support of our fundraising campaign to develop a DNA test for Glaucoma. Hopefully you will now have a better understanding of how this condition works and the effects it has on our wonderful breed. Many of you may ask why we are seeking a new test when we already have the Gonioscopy testing regime in place? Well, whilst this testing is a good indicator, it is exactly that, an indicator. It is not capable of predicting with 100% certainty if a dog will develop Glaucoma in its lifetime. Some may be on the risk scale and never go on to develop the condition, whilst others that are showing no risk at all suddenly find they are affected by it and lose their sight.
The Spanish Water Dog Club have partnered with the Canine Genetics Team at the Animal Health Trust (AHT) and the Eye Veterinary Clinic at Leominster to specifically identify the gene in Spanish Water Dogs that is responsible for Primary Hereditary Glaucoma/ Goniodysgenesis. They have previous experience in this field having successfully worked with the Border Collie Club to both identify the gene within their breed and develop a DNA Test that conclusively shows if a dog has/will develop the condition.
Each and every donation helps fund and support the research and develop our own breed specific DNA test. With it owners and breeders will be better informed and more capable of making choices to eradicate this horrible disease from the breed. It will also allow you to know whether your dog has this condition, so you can understand and predict future behavioural changes in you dog and seek the right support at the right time when you will need it the most.
I know what some of you may be thinking, there will be plenty of others who will see this and donate so I don’t need to. But if everyone thinks like that then we get no support. We are only a relatively small breed in number and need everyone’s support to make this happen. No matter how big or small every little helps. So here is the link again and please remember to share it with your friends.
Finally, the second part of our campaign will require the participation of as many SWD owners as possible. In addition to fundraising, the research is heavily dependent on collecting as large a sample as possible for the genetics team to work from to identify the specific gene. The more samples they have the easier it is for them to find it.
In the near future, Covid restrictions permitting, the club will publish details for a proposed eye testing and DNA collection exercise in November and December to support the research at the Eye Veterinary Clinic in Leominster. This will also support the ultrasound-based study aimed at surveying the deeper drainage angle and helping to stage disease. We would appreciate as many owners as possible to get involved.
The club wish to thank Rose Linn-Pearl BVsc Dip ECVO MRCVS at Eye Veterinary Clinic at Leominster, the BVA and Kennel Club and Thomas Boillot, Serge G. Rosolen, Thomas Dulaurent6., Frederic Goulle, Philippe Thomas, Pierre-Francois Isard, Thierry Azoulay, Stephanie Lafarge-Beurlet, Mike Woods, Sylvie Lavillegrand, Ivana Ivkovic, Nathalie Neveux, Jose-Alain Sahel Serge Picaud, Nicolas Froger for the reports that helped to produce this blog.