LYCOS RETRIEVER 
Deafness: Loss
built 642 days ago
Deafness is the condition of not being able to hear. In the United States those with the disability of deafness are entitled to certain government programs to help them due to the limitations imposed upon them by their disability. The legal definition of deafness in America is not absolute loss of hearing, but an inability to hear up to an acceptable level even with corrective devices.
Source:
Deafness generally refers to a physical condition manifested by a lack of sensitivity to sound. Legally, deafness is defined by levels of hearing loss whose severity is measured by the degree of loudness (or decibels) a sound must attain before it is heard by an individual. Mild deafness ranges from 10 dB to 30 dB, moderate deafness ranges from 30 dB to 60 dB, severe deafness ranges from 60 dB to 90 dB, and profound (or total) deafness ranges from 90 dB to 120 dB or more. Both severe and moderate deafness are commonly referred to as partial deafness, while mild deafness is usually referred to as hard of hearing.
Source:
Deafness can ... result from environmental factors or a combination of genetic and environmental factors. Environmental causes of hearing loss include certain medications, specific infections before or after birth, and exposure to loud noise over an extended period.
Source:
Deafness refers to a physical condition of a lack of sensitivity to sound. In legal terms, deafness is defined by degree of hearing loss. For example, profound or total deafness is 90 dB - 120 dB or more of hearing loss, whereas a moderate hearing loss is a loss of 30 dB - 60 dB. Severe and moderate deafness can be referred to as partial deafness or as hard of hearing, but mild deafness is usually referred to as hard of hearing.
Source:
The causes of nonsyndromic deafness can be complex. Researchers have identified more than 30 genes that, when mutated, may cause nonsyndromic deafness; ... some of these genes have not been fully characterized. Many genes related to deafness are involved in the development and function of the inner ear. Gene mutations interfere with critical steps in processing sound, resulting in hearing loss. Different mutations in the same gene can cause different types of hearing loss, and some genes are associated with both syndromic and nonsyndromic deafness. In many families, the gene responsible for hearing loss has not been identified.
Source:
Congenital hereditary sensorineural deafness is usually seen in dog and cat breeds with white pigmentation. In the small number of canine breeds where it is not associated with white pigmentation (Doberman and other dog breeds not carrying piebald or merle genes),23 deafness results from the type of hair cell loss that is a primary event with unknown cause. In breeds of dogs carrying the piebald or merle genes and breeds of cats carrying the white gene, the hair cell loss is secondary to degeneration of the cochlear blood supply. Figure 1 shows a cross section of one turn of the cochlea, demonstrating the separation of the cochlea into three parallel ducts: the scala vestibuli, the scala media (or cochlear duct), and the scala tympani which joins at the apex of the cochlea with the scala vestibuli. The outer margin of the scala media is covered by a vascular bed, the stria vascularis. The stria is responsible for secretion of endocochlear fluid and maintenance of its high K+ concentration which is essential to sound transduction by the sensory hair cells.
Source:
MORE ABOUT
Loss