Health screening for multi-ocular defects in dogs

Virtually all pedigree dog breeds have increased risk factors for certain hereditary health conditions that are prevalent or appear more often than would occur by chance across the breed in question as a whole, and a great many of these conditions affect the eyes.

Certain dog breeds also draw the short straw in that they are at risk for several different hereditary eye disorders rather than just one, and the term that vets and laboratories often use to refer to clusters of unrelated eye conditions that are all considered to be a risk to any given breed is multi-ocular defects.

Knowing if any potential parent dog that a breeder might be considering using within a mating match to produce a litter is affected by a hereditary eye disorder, or a carrier for an eye disorder – or appears to have healthy eyes but has a condition that will only become apparent later in life – allows breeders to make an informed decision about which dogs to breed from.

This in turn means that breeders can choose to remove dogs who are affected by or carriers of potentially serious eye disorders from the available breeding stock and so, avoid them passing such conditions on to their own litters.

However, there is no catch-all DNA test or definitive screening protocol that can identify or rule out the presence or absence of all of the potential eye disorders that have been identified in dogs, and so in at-risk breeds, multi-ocular defects eye screening may be required.

This means screening and testing the dog in question for a range of different disorders, which usually means a range of tests and examinations must be performed, and also, that they many need to be performed more than once throughout the dog’s life.

This is because some hereditary eye disorders and conditions cannot be definitively identified with a DNA test, but only be eye examination and screening – and for certain eye disorders, a dog might appear to be clear of the condition when they are young, but develop the symptoms that enable diagnosis of the condition as they get older.

In this article, we will look at multi-ocular defects in dogs in more detail, including what type of eye disorders are involved, how they are tested for, and what sort of dogs are at the greatest risk for inheriting multi-ocular defects. Read on to learn more.

What are multi-ocular defects in dogs?

The term multi-ocular defects – sometimes referred to as multiple ocular defects – refers to a range of different, separate defects or health conditions that affect the eyes. It is a catch-all title used to refer to the presence of, or risk for, the dog developing one or more of a number of eye disorders, rather than the name for a certain condition or cluster of conditions of the eyes.

Exactly which eye disorders fall under the remit of multi-ocular defects can of course vary, but some of the most common problems include:

• Retinal dysplasia.
• Congenital cataracts.
• Persistent pupillary membrane or PPM.
• Microphthalmia.
• Progressive retinal atrophy.
• Hereditary glaucoma.

This list is not exhaustive, but it covers some of the most common hereditary eye disorders that can affect dogs, and which are prevalent within certain dog breeds. The nature of multi-ocular defects in dogs means that at-risk dogs may not have heightened risk factors for all of these conditions (or any others), but that they may be at risk for two or more of them.

What type of dogs are at risk of multi-ocular defects?

Any dog, regardless of their breed or pedigree status may inherit or develop eye disorders – but some dog breeds are particularly prone to developing one or more eye disorders that are passed on through the bloodline from parent dogs to their young, and so, can be considered to be at risk of inheriting multi-ocular defects.

Some of the dog breeds that are the most widely recognised as being at risk for multi-ocular defects include:

• The bloodhound
• The old English sheepdog
• The cocker spaniel
• The Akita

Again, this list is not exhaustive, but serves as guidance for owners and breeders of dogs of these breeds in particular.

How are dogs tested for multi-ocular defects?

Just as multi-ocular defects is not one condition but rather many, there isn’t one catch-all test to tell owners and breeders of dogs their own dogs’ status. There are various different types of canine eye tests and screening protocols in place, some of which take the form of DNA tests that return a definitive result that won’t change over time.

However, not all canine eye disorders that can be passed on from parent to offspring can be definitively diagnosed in this way, and some conditions rely upon physical examination and screening to diagnose the presence or absence of the condition at the time of the examination.

This means that for eye problems of certain types, a dog’s status can change over time – they might get a clean bill of health for a certain condition when they are young, but be identified with symptoms of one or more problems as they get older.

This in turn means that dogs from breeds that are at risk of conditions that must be screened rather than DNA tested may need to be screened more than once – generally for breeds with the greatest risk, screening is advised to take place no longer than a year prior to breeding from them.

This doesn’t return a definitive result, because as mentioned, a condition may not become apparent until later in life, by which time the dog may already have bred and passed it on – but it helps to reduce the incidence rate of the condition in litters, because dogs showing symptoms of a problem can be removed from the breeding pool.

You can find out more about eye health, DNA testing and screening in dogs of all breeds – including how tests are performed for multi-ocular defects and individual conditions – within this publication from the British Veterinary Association.