2.2 Design & Setting
This retrospective observational study recruited Korean adults with AHL
who purchased a hearing aid at one secondary-referral, university-based
hospital. The inclusion criteria were as follows: (1) 19 years old or
above; (2) ear anatomy compatible with wearing a conventional hearing
aid; (3) AHL, as defined above; (4) hearing aid fitted to the worse ear;
and (5) sensorineural or mixed type HL. The exclusion criteria were as
follows: (1) conductive hearing loss; (2) observed neurological or
psychiatric disorder; (3) fluctuating hearing loss; (4) self-reported
physical or mental health unsuitable for hearing aid fitting and use;
and (5) inadequate cognitive competence for responding to
questionnaires.
At 1, 2, 3, 6 and 12 months after purchase, hearing aid was fitted using
the National Acoustic Laboratories (NAL) formula. The degree and type of
hearing loss were classified using PTA4 and the criteria
set by the World Health Organization.10 AHL was
defined as hearing loss with an interaural threshold difference of 15 dB
or greater in the PTA4.9
Cases of AHL were classified into four subgroups according to the
criteria defined in Table 1. Our classification modified previous
studies of Van de Heyning, et al.9 Because single
sided deafness (SSD) subgroup is a poor candidate for hearing aid, we
excluded SSD cases and analyzed cases of three subgroups (unilateral
hearing loss (UHL), and asymmetrical hearing loss type 1 (AHL1) and type
2 (AHL2)), which were classified based on the poorer ear
PTA4 of 70 dB HL and the better ear PTA4of 30 dB HL.
Twelve months post-fitting, performance of hearing-aid use was evaluated
and classified into three groups: (1) successful users, (2) intermittent
users, and (3) failed users. Successful users met all of the following
criteria: (1) wearing the hearing aid for more than four hours per day;
(2) wearing the hearing aid for twelve months or longer after purchase;
(3) showing an improved speech discrimination score more than 2% in the
HINT; (4) showing improved sound localization; and (5) scoring 21 points
or more in the IOI-HA.11 Patients who stopped using
within the first twelve months after purchase were classified as failed
users. Cases that did not meet the criteria for either successful and
failed users were considered intermittent users.