Types
A common tinnitus classification is into "subjective and objective tinnitus". Tinnitus is usually subjective, meaning that the sounds the person hears are not detectable by means currently available to physicians and hearing technicians. Subjective tinnitus has also been called "tinnitus aurium", "non-auditory" or "non-vibratory" tinnitus. In rare cases, tinnitus can be heard by someone else using a stethoscope. Even more rarely, in some cases it can be measured as a spontaneous otoacoustic emission (SOAE) in the ear canal. This is classified as objective tinnitus, also called "pseudo-tinnitus" or "vibratory" tinnitus. Subjective tinnitus
Subjective tinnitus is the most frequent type of tinnitus. It may have many possible causes, but most commonly it results from hearing loss. When the tinnitus is caused by disorders of the inner ear or auditory nerve it can be called otic (from the Greek word for ear). These otological or neurological conditions include those triggered by infections, drugs, or trauma. A frequent cause is traumatic noise exposure that damages hair cells in the inner ear.When there does not seem to be a connection with a disorder of the inner ear or auditory nerve, the tinnitus can be called non-otic (i.e. not otic). In some 30% of tinnitus cases, the tinnitus is influenced by the somatosensory system, for instance, people can increase or decrease their tinnitus by moving their face, head, or neck.
The test determines whether the mutated copy of SOD1 is present in the DNA sample submitted. It must be interpreted with caution by a veterinary clinician in combination with the animals clinical signs and other lab test results. The results reported are:

Normal / Normal (N/N, or clear): The dog does not have the mutation and is extremely unlikely to develop degenerative myelopathy. There have been cases, however, in which dogs that tested clear were found to have DM upon necropsy. Normal / Abnormal (N/A or carrier): The dog has one mutated copy of the gene (is heterozygous) and is a carrier but will not have degenerative myelopathy though there has now been some cases of heterozygous carriers developing DM. It will be possible for it to pass the mutation to offspring. A thorough examination of the dogs pedigree and DNA testing should be undertaken prior to breeding a dog with this result. Abnormal / Abnormal (A/A or At Risk): The dog has two copies (is homozygous) for the mutation and is at risk for degenerative myelopathy. Genetics
Breeding risks for degenerative myelopathy can be calculated using the Punnett Square:

If both parents are clear (N/N) then all of the puppies will be clear. If one parent is a carrier (N/A) and one is clear (N/N) each puppy has a 50% chance of being clear and a 50% chance of being a carrier.