Though it is a congenital disease, the cause for it is still unknown. The membranes that are present in the eye before birth are actually remnants of capillaries that provide nutrients necessary for lens development. In Tibetan Mastiffs, these membranes can remain in the eye even after four or five weeks of age when they are supposed to be completely gone. Despite it being essentially harmless, these formations can cause problems with vision. These string-like structures can start becoming less visible as a Tibetan Mastiff puppy gets older. Even if they do not fully disappear, it is less likely the dog’s vision will be affected. Suppose no serious symptoms develop as a result of PPM. In that case, hyperosmotic drops are usually prescribed to reduce any potential swelling, but surgery is the best option for dogs with cataracts that may appear because of PPM.