Since Zwaardemaker in 1889 first described the clinical manifestations of high tone deafness with aging there have: been a number of reports on presbycusis.
This presbycusis has become increasingly important in recent years for 3 main reasons:
1) The aging populations are becoming a larger proportion of total population, because of development of medicine.
2) The development-production of machines and other devices which can generate over-all sound pressure levels of 130 dB. or more re 0.0002;dynes per square centimeter, and
3) Certain state court rulings which hold that industrial deafness is an occupational disease, thus entitling the affected worker to a schedule award under the Workman´s °Compensation Law.
The present study was performed to determine the normal thresholds of hearing for pure tones on an age-stratified sample of subjects drawn from 280 cases between the ages of 20 to 89 who gave no history of significant noise trauma or disease.
It was anticipated that the data obtained in this study would contribute new information on the basic issues particularly with respect to the establishment of an appropriate reference level for normal hearing of pure tones in Korea.
The subjects tested in the hearing survey were selected from 7 age cathegories: 1) 20 to 29 years; 2) 30 to 39 years; 3) 40 to 49 years; 4) 50 to 59 years; 5) 60 to 69 years; 6) 70 to 79 years; and 7) 80 to 89 years. The subjects were taken from
1) undergraduate student population at Yonsei medical college in 20 to 29 age group,
2) doctors and nurses in Severance Hospital in 30 to 39 age group,
3) relatives of patients who visited at O.P.D. of Severance E.N.T. in 40 to 49 age group, and
4) the old of a public assistance institution in 60 to 89 age group.
The 3 step process required of each subject included;
1) completing a hearing survey questionnaire which contained 3 major parts of background data (residence, occupation, military service and hobbies), Aural History (familial deafness, illness, accidents and operations) and Present hearing status (effect on telephone use on hearing, tinnitus and diplacusis).
2) obtaining an otological examination, and
3) taking an audiometric test.
All subjects, passed the 2 step examinations were tested on a Beltone Audiometer, Model 15 C, which was calibrated by Rudmose RA 106.
At each frequency, the threshold was crossed in a series of 2 ascending and 1 descending trials. Nine test frequencies were used and were presented to all subjects in the following order: 1. 000 cps, 2, 000 cps, 3, 000 cps, 4, 000 cps, 6, 000 cps, 8, 000 cps, 1, 000 cps, 500 cps, and 250 eps. The results are as follows:
1) For both men and women, there is a decrease in hearing sensitivity with increasing age and a progressive spreading of the loss from higher to the lower frequencies.
Hearing loss in 50 age group reveals 42.5 dB. to 45.0 dB. at 8,000 cps.
2) The differences between sexes are most marked at the higher frequences, with the cross-over point in the region of 2, 000 cps.
The women has poorer hearing than men above 2, 000 cps.
3) There are significant differences (average 9.2 dB.) between the average sensitivity of right and left ears.
Left ears are poorer hearing than right ears.
4) Audiogram pattern reveals abrupt form (96.5%), flat form (2. 1%) and descending form(1. 4%).
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