Types of Hearing Loss

Hearing loss is generally categorized by two main types: sensorineural and conductive. There are certain instances where both types occur simultaneously, and this type is termed mixed hearing loss.

Sensorineural hearing loss

Sensorineural hearing loss results from dysfunction within the inner ear known as the cochlear (sensory) or with the nerves (neural) sending sound to the brain. Causes of this type of hearing loss include:

Congential factors

• Prenatal infections - toxoplasmosis, rubella, cytomegalovirus, herpes, or syphilis
• Maternal diabetes
• Genetic factors and syndromes the child has at birth
• Low birth weight and prematurely
• Hereditary - in the family 

Acquired

• Loud noise exposure
• Injury/trauma
• Infections
• Tumors affecting the hearing nerves
• Certain medications that cause damage to the ears

Conductive hearing loss

Conductive hearing loss occurs when there is a problem in the outer or middle ear which limits the sound waves from being sent to the inner ear correctly. In children, conductive hearing loss is typically the most common type. Factors that may cause this type of hearing loss are:

Congenital factors

• Anomalies of the pinna (the outside of the ear)
• Anomalies of the tympanic membrane (eardrum)
• Anomalies of the external ear canal
• Anomalies of the ossicles (the three tint bones that deliver the sound waves to the middle ear)

Acquired

• Excessive wax
• Ear infections such as otitis media
• Chronic ear infections with fluid in the middle ear
• Perforation of the ear drum
• Problems with the eustachian tube
• Foreign bodies in the ear canal, such as beads or popcorn kernels
• Tumors of the middle ear

Degree of hearing sensitivity

With diagnostic hearing tests, the objective is to determine the softest level that the patient can hear at across a range of different frequencies (pitches) and speech. Based on the determined levels, hearing is then categorized into degrees:

• Within normal limits ≤ 20dB
• Mild 25-35 dB
• Moderate 40-50 dB
• Moderately-Severe 55-65 dB
• Severe 70-85 dB
• Profound ≥ 90 dB