PERSISTENT PUPILLARY MEMBRANES

During the embryological development of the eye, the iris initially forms as a solid sheet of mesodermal tissue. This is called the pupillary membrane. Later on, some of this mesodermal tissue dissipates, and this results in the formation of the pupil.

Sometimes, after birth, a few of these fine strands of pupillary membrane remain. It is not unusual to see such pupillary membrane remnants in 6-to-8 week old puppies, however, if they persist beyond this age they are then are described as persistent pupillary membranes (PPM) and are considered to be defect.

The most common manifestation of Persistent Pupillary Membrane is a fine strand of pigmented tissue which arises from the iris collarette and attaches to another spot on the iris. Sometimes the strand will cross the opening of the pupil. In more serious cases, the PPM arises from the iris and attaches either the the lens - where it may produce a cataract, or to the inner surface of the cornea - resulting in corneal damage, scarring or persistent corneal edema. In the latter cases, impairment of vision may occur.

In several breeds including the Basenji, the Chow Chow and the Pembroke Welsh Corgi, this defect has become common enough to be considered a major inherited ocular disease.

Persistent Pupillary Membranes (PPM) frontal and cross section views illustrating variations.

a. One end of PPM floating in anterior chamber
b. Iris to lens PPM resulting in capsular cataract
c. "Y" shaped iris to iris band
d. Single iris to iris band
e. Iris to cornea PPM resulting in adherent leukoma of the cornea.

Breeds Affected with PPM's
BREEDING ADVICE
BREED	NO*	OPTION*	UNKNOWN*
Australian Cattle Dog	.	.
Australian Shepherd	.		.
Basenji		.	.
Basset Griffon	.		.
Bullmastiff	.		.
Chow Chow		.	.
Cocker Spaniel	.		.
Collie	.		.
Dalmatian	.	.
German Shepherd	.	.
Irish Setter	.	.
Jack Russel Terrier	.	.
Mastiff		.	.
Minature Bull Terrier	.		.
Neopolitan Mastiff	.		.
Norbottenspets	.		.
Portuguese Water Dog	.		.
Puli	.		.
Scottish Terrier	.		.
Shetland Sheepdog	.		.
Shiba Inu	.		.
Soft Coated Wheaton Terrier	.		.
Welsh Corgi (Cardigan)	.		.
Welsh Corgi (Pembroke)		.	.

* Definitions

(abstracted from Ocular Disorders Proven or Suspected to be Hereditary in Dogs, ACVO, revised 1994)
NO - Substantial evidence exists to support the heritability of this entity and/or the entity represents potential compromise of vision or other ocular function.
BREEDER'S OPTION - Entity is known or suspected to be inherited but does not represent potential compromise of vision or other ocular function
UNKNOWN - Diseases under consideration with inadequate information available to give breeding advice.

Reference

Severin, G.A., Severin's Veterinary Ophthalmology Notes 3rd edition, 1995.

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Updated: Saturday, October 27, 2001

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