(a) "Deaf" means severe to profound impairment of the sense of hearing whereby the understanding of speech is unattainable through the ear alone with or without amplification, and visual communication is used as the primary mode of communication.
(b) "Hard of hearing" means significant impairment to the sense of hearing, but not to the extent that the person must rely primarily on visual communication.
(c) "Hearing-impaired" means persons who are either deaf or hard of hearing.