Persistent Pupillary Membrane or PPM in dogs

A pupillary membrane is the remnant of a blood vessel that delivered nutrients to the eye of the dog in question while they were in utero, or prior to birth. These membranes remain present after birth, but usually disappear on their own by the time the pup in question has reached a month to six weeks old.

However, in some affected dogs, the pupillary membranes don’t disappear on their own, and continue to occlude the eye, which can affect the dog’s vision and lead to secondary problems like cataract development. This is called persistent pupillary membranes, or PPM, and some dogs will have visible signs of PPM in their eyes even when adult, without suffering from any issues as a result of this.

However, if you are about to buy a puppy or even if you own an adult dog, it is a good idea to learn a little bit about PPM in dogs, how to identify them, and what can be done about them.

In this article, we will look at PPM in dogs in more detail, including explaining what sort of dogs are most at risk of the condition. Read on to learn more.

More about persistent pupillary membranes in dogs

The membranes for which PPM is named are made of old blood vessels that supported the development of the eye in foetal pups, and which usually go away on their own after pups are born.

However, in pups that still show signs of PPM by the time they are a few months old, the membranes themselves can have a range of different effects, depending on how they attach to the eye and where they are located.

• Some persistent pupillary membranes cross the eye’s pupil and are attached at two points on the iris of the eye.
• Some strands may cross the pupil and have attachments at the lens and iris respectively.
• Some strands pass between the cornea and the iris.
• Free-floating PPM consists of strands that attach on one side to the iris of the eye, with the other end floating freely across the front of the eye.

What causes the condition?

Persistent pupillary membranes in dogs are a type of birth defect or congenital anomaly, which means that they are present from birth, and naturally remain within the eyes of most pups up until the pup begins to open their eyes for the first time, at which point any PPM present will usually disappear without incident over the next couple of weeks.

However, when pups retain the membranes past this point, the condition usually has a hereditary cause, with an unknown mode of inheritance which means that there is no definitive way to tell prior to breeding if any given mating match are likely to produce pups with the disorder themselves.

An adult dog that still possesses persistent pupillary membranes as an adult, whether or not they cause a problem for the dog, should not be bred from due to the elevated risks of passing the condition on to their own offspring.

What sort of dogs are at risk of PPM?

Because all pups are born with pupillary membranes that generally shrink and disappear over time, any pup of any breed or type has the potential to develop the condition. However, a litter who has one or both parents with the condition has a higher chance of retaining their pupillary membranes themselves.

Within certain dog breeds, persistent pupillary membranes are known to be a breed-specific concern, with higher than normal occurrence rates within the breed, and elevated chances of the condition causing acute and serious problems such as blindness in affected dogs.

Some breeds with an elevated genetic predisposition to PPM are the Bullmastiff,Basenji, Pembroke Welsh corgi, Yorkshire terrier and Chow-Chow.

Persistent pupillary membranes symptoms

If you are caring for a litter of pups prior to their going onto their forever homes or are buying or adopting a puppy, it is important to know the symptoms of persistent pupillary membranes, so that you can spot a problem in the making, seek advice, and make an informed decision on how to proceed.

The main symptoms of PPM in dogs are as follows:

• Imperfect vision or partial vision, which can affect the pup’s learning and development due to their visual disadvantage.
• Visible strands crossing or floating across the pupil of the eye from one side to the other.
• A foggy or cloudy appearance across the cornea, such as is often associated with cataract development in older dogs.
• Erratic or abnormal movement and focus in the eyes as the pup attempts to counteract the effects of the strands obscuring their vision in order to see normally.

Not all of these symptoms will be present or obvious in all affected pups, and particularly in the case of small pups with small eyes or breeds with deep set eyes or fringes of hair that obscure their eyes, checking the eyes for problems is particularly important.

It is also wise to ask your vet to check the pup over when they are a few weeks old or shortly after you make a purchase, in order to pick up on any anomalies quickly.

Diagnosis and treatment of persistent pupillary membranes in dogs

When diagnosed in younger dogs under the age of around six months, owners are usually advised to wait a while to see if the membranes shrink and disappear on their own as the dog gets a little older, which is very common.

However, if the membranes persist and it becomes apparent that they will not resolve themselves, this can be problematic as at present there is no recognised method to safely remove them from the eyes. PPM is not painful for dogs, but it can affect their quality of life if it obscures their vision, which for some dogs, can be serious enough to cause partial or full blindness.

If the strands cause clouding of the cornea in a similar manner to cataracts, it may be possible to have this removed and corrected surgically by a specialist veterinary ophthalmologist, but again, this is not hugely common and there are only a limited number of specialists in the UK who are able to perform this procedure.