The Eyes Have It - PERSISTENT PUPILLARY MEMBRANES
Persistent pupillary membranes (PPM's) are the remnants of a normal embryologic
structure of the eye. During fetal development they are continuous with the blood
supply of the developing lens. The pupillary membrane begins to atrophy during fetal
life, but atrophy may not be complete until 4 to 8 weeks of age. These strands are
considered to be "persistent" when they do not regress by 8 weeks of age.
There are four variations of PPMs:
- Iris to iris. The strand is attached to only iridal tissue, not touching the lens or cornea.
- One end attached to iris, the other not attached (free floating).
- Iris to lens.
- Iris to cornea.
The 3rd and 4th variety usually have an opacity where the strand attaches to either the lens
or cornea. If severe, any of the 1, 3, and 4 types can cause visual impairment. The vast
majority of PPMs are iris to iris and do not cross the pupil. These do not cause any clinical
problems for the dog (are not "clinically significant"), but may be of significance in selecting
breeding stock.
PPMs are known to be inherited in the Basenji breed, where there is a high incidence
of affected dogs. Several other breeds, including the Mastiff are suspected to have familial
PPMs.
Ideally, Mastiffs affected with PPMs should not be bred, so as to limit the incidence and
severity of the problem in the breed. Unfortunately, the mode of inheritance is unknown.
Currently, PPMs are considered to be "breeder option" by CERF, and dogs with PPMs currently
will be eligible for CERF numbers. This, however, may change in the future.
The key points to remember are these:
- PPMs that are present after 8 weeks of age are significant.
- Most PPMs will cause no clinical problem for the dog.
- Ideally, dogs with PPMs should not be bred.
Our next eye disorder to be featured here will be cataracts. Thank you to Dr. Meek for her
time and effort to present this valuable information to us.
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