A Study on the Deaf-Mute in Formosa, Especially on their hearing

334 students of the School for the Deaf-Mute in Taipei, Taiwan have been dealt with in the present study. 201 out of 334 or 60.2% were males, while 133 or 39.8% were females. 81 out of 334 or 22.7% were congenitally deaf, while acquired deafness was found in 220 or 67.4%. The ratio of congenital deafness to acquired deafness was not significantly different between 2 sexes. Attempts were made to determine the cause of deafness by studying questionnaires answered by the parents. Heredity was the cause in 35 or 43.2% of 81 congenitally deaf cases. Prenatal quinine intoxication and birth injuries were the causes in small number of cases. Causes were unknown in 41 or 18.6%. Febrile diseases, meningitis and measles were most prominent as the cause of acquired deafness, each accounting for 19.09%, 18.64% and 13.18% of the entire acquired deafness cases. Otitis media was the fourth in ranking. It is a remarkable fact that T. B. Meningitis together with Streptomycin intoxication caused deafness in approximately 10% of the acquired deafness cases. More than half of the acquired deafness cases had lost hearing before or at the age of 3. Of the total ears numbering 668 on which pure tone audiometry was done, 40% were totally deaf, while the ears with residual hearing were 60%. Of the total cases, 50% had residual hearing binaurally, 20% had residual hearing monaurally and the remaining 30% showed binaural total deafness. The incidence of binaural residual hearing was about equal in congenital and acquired deafness group, but binaural total deafness was more frequent in the latter group. A study on the incidence of residual hearing for each test frequency revealed the highest incidence for 500 cps., decreasing in order of 250-, 1,000-, 125-, 3,000-, 2,000-, 4,000- and 8,000 cps. in total ears as well as in acquired deafness group. The incidence of residual hearing is higher in congenital than in acquired deafness group throughout the entire frequency range, the difference being most marked over the middle tone range. The order of incidence of residual hearing for each test frequency is almost similar in both groups except that the incidence is very slightly higher at 2, 000cps. than at 3,000cps. in congenital group. Test of vestibular function was done by observing nystagmus elicited by caloric stimulation on 263 cases, i. e. 526 ears. There was no response whatsever in 40% of the total ears thus tested, 23% of congenital group and 50% of the acquired deafness group. The incidence of positive response was higher in the ears with residual hearing than in totally deaf ears. In the present series of cases, there were comparatively more students skilled in lipreading in the group of cases whose deafness started during 6 to 9 years of age than in the group of cases born deaf or whose deafness began at or before the age of 5. The difference, however, has no definite statistical significance. There were more good lip-readers in the group of cases with residual hearing for 2 or 3 speech frequencies than in the group of cases with residual hearing limited to 1 speech frequency and the cases without any hearing for all speech frequencies. In order to clarify the indications for the use of hearing aid by the present series of cases, 2 factors were considered; firstly the average value of the hearing loss at 3 and at times 2 speech frequencies, and secondly the shape of audiogram. Of the total 334 cases use of hearing aid was not indicated in 113 cases who were totally deaf at 3 speech frequencies and 70 cases with residual hearing only at 1 speech frequency; both together constituting 54.8% of total cases. The remaining 221 cases were considered to be candidates for the use of hearing aid. They were divided into the following 3 classes according to the degree of hearing loss. 1. Ideal cases regarding the use of hearing aid. Hearing loss of less than 60 db.