A statistical analysis was made on 233 cases of unilateral perceptive deafness whose causes were unknown in 4 years between 1973 and 1976. The following results were obtained.
1) The rate of occurrence was found in 0.8% of the out-patients, in 5.4% of perceptive deafness, and in 41.7% of unilateral perceptive deafness of known and unknown causes.
2) The male cases were 52.8% and female 47.2%.
3) The age of occurrence was 5-9 years old in the total deaf group, and there was a peak of the occurrence at the young age groups. In the other groups, there was the two-phase distribution of occurrence with one peak at the young age of 5-9 years and the other at the age of around 30.
4) The possibility of a heredity factor was found in 9% and slightly frequent in females.
5) There was no characteristic audiogram in those who were suspected to have a hereditary deafness.
6) The heredity pattern was not simple.
7) Regarding the hearing patterns, more than half were of the total deaf, while high tone hearing loss came to next in number.
8) The most of patients with unilateral perceptive deafness which occurred in their young ages did not have tinnitus or dizziness.
9) There were cases whose hearing loss were altered or improved.
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