During development, the iris (colored portion inside the eye) first forms as a solid sheet of tissue. Late in gestation a breaking down of tissue takes place to form the pupil. If some of these fine strands of tissue remain they are described as persistent pupillary membranes (PPM). It is not unusual to see such strands in 6-to-8 week old puppies or kitties. However, if they persist beyond this this age they are considered a defect. They can form attachments between the cornea and/or the lens resulting in opacities and cataracts and can cause vision defects. In the Basenji and Mastiff breeds, this anomaly has reached such proportions as to be considered a major inherited ocular disease. In 6-to-8 week old Basenji and Mastiff puppies if the strands are extremely large or if they persist beyond the 12th week a note should be made on the examination form. This problem is becoming more recognized within the Collie breed. Other breeds may have individual animals with PPM as a problem.
The arrows point to persistent pupillary membranes in this dog. The adjacent white specks are scars on the inside of the cornea due to the membranes touching the cornea.
This cat has persistent pupillary membranes pointed out by the arrows. The persistent pupillary membranes lead from the iris to the lens where they are causing a focal cataract.
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Dennis Hacker via E-mail:
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