A 34-year-old man comes to the ·office for evaluation of hearing loss. The patient is a military pilot who has flown the past 8 years in noncombat zones. Regular hearing tests administered by the military have been normal until his most recent one. The patient has noticed no change in his hearing and has no ear pain, tinnitus, or vertigo. The results from the remainder of his annual physical, mental, vision, and cardiac tests were normal. The patient has no medical conditions and takes no medications. Aural examination shows clear, intact tympanic membranes bilaterally with no middle ear effusion. Review of the audiometry reveals a mild, bilateral, high-frequency hearing loss.