Carha's notch in audiometery is seen in:

Carhas notchBone conduction is normal in otosclerosis.In some cases there is a dip in bone conduction curve which is maximum at 2000 Hz / 2 KHZ called as Carhas notch.Carhas notch is seen only in bone conduction curve.It disappears after successful stapedectomy/stapedotomy. The reason why it disappears after successful surgery is that when the skull is vibrated by bone--conduction sound, the sound is detected by the cochlea 3 routes:- Route (a)--is by direct vibration within the skull.- Route (b)--is by vibration of the ossicular chain which is suspended within the skull.- Route (c)--is by vibrations emanating into the external auditory canal as sound and being heard by the normal air-conduction route.In a conduction type of hearing loss (as in otosclerosis) the latter two routes are deficient but regained by successful reconstruction surgery. Hence bone conduction thresholds improve following surgery.