To understand hearing loss it is important to be aware of the five levels of deafness: mild, moderate, severe, profound and total. According to http://www.neurelec.com, in mild deafness (hearing loss of 20 to 40 dB) speech is perceived in a normal voice but is difficult to perceive when in a low or distant voice. However, the majority of familiar sounds are perceived. In moderate deafness (hearing loss of 40 to 70 dB) speech is perceived if the voice is loud and the individual understands better if they can see the individual speaking. In severe deafness (hearing loss of 70 to 90 dB) speech is perceived in a loud voice close to the ear. In profound deafness (hearing loss of 90 to 120 dB) speech is no longer perceived at all only very loud sounds are perceived. Lastly, in total deafness (hearing loss above 120) no sound is perceived. There are also three types which include: transmission, perception and mixed. Transmission deafness results from a deficiency of the outer or middle ear and can be often treated by surgery or use of a hearing aid. Perception deafness results from a deficiency in the inner ear or the nerve pathways. Hearing aids and cochlear implants are often used to treat perception deafness. Mixed deafness is common and results from a combination of transmission and perception deafness.
Over 48 million individuals across the US have hearing impairments and this statistic only includes Americans 12 and older that have had their hearing tested. There are several genetic factors that are believed to be the cause for over 50% of congenital hearing loss. Inherited hearing loss may be autosomal dominant, autosomal recessive or X-linked which is related to the sex chromosome. In autosomal dominant hearing loss, one parent who carries the gene for hearing loss passes it onto the child. In such a case there is a 50% probability that the child will have hearing loss. The probability increases if both parents have the dominant gene. In autosomal recessive hearing loss, both parents who have normal hearing, carry a recessive gene. Because the gene is recessive the child’s probability of hearing loss drops to 25%. In X-linked hearing loss, the mother carries the recessive gene for hearing loss on the sex chromosome and passes it on to only males.
-Sarah Rohler
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