Persistent Pupillary Membranes (PPM) in Dogs

Persistent pupillary membranes, or PPM, are a normal part of the embryonic growth of most species.  This membrane is initially a solid sheet of mesodermal tissue which  disappears to form the pupil under normal developmental circumstances.  Sometimes, however, this tissue doesn’t totally disappear and strands of it become attached to other adjacent parts of the eye, causing problems with the normal functioning of those parts.

Persistent pupillary membranes, or PPM, are strands of pigmented tissue which arise from the iris collarette which attaches to another surface of the iris, or lens or cornea of the eye, whether in canines, humans or other species.

Here are some of the symptoms which might be noted in a dog with persistent pupillary membranes or PPM:

• Visual impairment
• Tiny strands may be noted crossing the pupil space, running from one side of the iris to the other side
• Corneal opacities or “foggy” or “cloudy” looking corneas
• Abnormal iris movement as it controls the light entering the eye

Some of the above symptoms may not be noticed at all, especially in puppies, as the physical appearance of the iris and pupil space can be very hard to assess in small puppies or small dog breeds.   

Types  

The mesodermal tissue which comprises the pupillary membrane at or before birth is vascular tissue.  This membrane usually disappears, forming the pupil of the eye, within 3 months of birth, but sometimes some of this vascular tissue remains and will cause problems in the canine eye as time goes on.  There are basically 4 types of persistent pupillary membranes:

• Iris to iris attachment - These vascular strands cross the pupil space in varying degrees and attach to another portion of the iris
• Iris to lens - These vascular strands come from the iris and go through the pupil space to attach to the lens of the eye, located behind the iris tissue
• Iris to cornea - These vascular strands come from the iris tissue and attach to the back side of the cornea or attach to the cornea in the anterior chamber angle, both areas being located in front of the iris
• Free floating - This type of vascular strand is attached to the iris on one end while the other end floats freely within the anterior chamber of the eye

As noted above, there are 4 types of persistent pupillary membranes in dogs and some of them can be visually devastating.  Here is a brief synopsis of how these vascular strands can affect your dog:

• Iris to iris attachment - These strands usually don’t cause any problems; they usually disappear or very nearly disappear on their own
• Iris to lens attachment - These strands attach the iris at one end and the lens of the eye at the other end, causing a minor cataract (a clouding of the lens of the eye) which will, in turn, cause a minor vision problem in your dog
• Iris to cornea attachment - These strands can cause more serious problems; they attach to the iris at one end and to the back side of the cornea at the other end, causing the cornea to become foggy and cloudy by damaging the inner layers of the cornea, which in turn, will cause devastating vision loss to your canine buddy 

Sometimes, puppies can be born blind due to the persistent pupillary membrane which hasn’t disappeared as it should.  Seek medical assessment if those membranes don’t disappear with 3 to 4 months of birth.

Diagnosis of persistent pupillary membranes will ultimately require the expertise of a veterinary ophthalmologist.  Your veterinary professional will need your input in the form of the history which will include any observations you have made in regard to visual activities of your canine buddy and any history of hereditary issues, if known.  He will likely use some microscopic instruments to assess the eyes of your canine, looking for any abnormalities or anomalies inside as well as outside the eyes.  

The vet may instill some dilating eye drops to dilate the pupils to take a look at the interior of the eyes.   In the event that serious abnormalities exist, he may make a referral to a veterinary ophthalmologist for further evaluation and possible treatment.  The veterinary ophthalmologist will likely need to do further testing and evaluations specific to his expertise to determine his ultimate diagnosis and treatment plan.

There is no real treatment for persistent pupillary membranes in dogs, some of them actually resolving on their own.  The clouding of the lens of the eye (cataract) that is caused by persistent pupillary membranes will not go away but they also don’t generally worsen.  However, the clouding of the cornea that occurs when the vascular strand attaches to the cornea will likely worsen, eventually completely blinding your canine.  If the expertise of a veterinary ophthalmologist has been obtained, depending on the result of his assessment and evaluation, there could be a surgical intervention option available.  

There has been some progress made in the removal of cataracts in the eyes of various animal species but it in no way mirrors the extent to which medical technology has come in this area in regard to the human cataract removal in terms of visual rehabilitation.  This option might be available only in the event that the cornea remains clear and the stage of cataract development is such that it interferes with the normal function of the animal in question.  Appropriate recommendations will be given and decisions made upon obtaining the diagnosis by whichever veterinary professionals are involved.

If you have a dog who suffers from this malady and that dog is over six months old, it is likely a hereditary problem.  If you have any problem which is considered hereditary, it is not recommended that the dog (male or female) in question be bred, preventing this trait from being passed along to offspring, compromising the integrity of the breed.  

That being said, it is important to note that having persistent pupillary membranes doesn’t necessitate any permanent action to remove or rid the afflicted animal from your home or kennel.  He will still likely be able to function as a family pet and engage in many doggie activities safely for many years to come.  This malady is not a death sentence for your beloved pet but rather may simply require some adjustments to be made in the lifestyle of the dog.  He still deserves to be loved and cared for and he will still love and care for his human family.