What is Usher syndrome?
Usher syndrome is a genetic condition that causes partial or total hearing loss and vision loss that worsens over time. Abnormalities in the ear fall under the classification of sensorineural. The loss of vision in Usher syndrome is caused by retinitis pigmentosa (RP), which affects the layer of light-sensitive tissue of the retina (the back of the eye). Vision loss happens as the light-sensing cells of the retina gradually deteriorate. An individual will typically find their night vision is lost, followed by blind spots that develop in their side vision. Over time, these blind spots enlarge and merge to produce tunnel vision. In some cases, clouding of the lens of the eye (cataracts) are formed. However, it's not uncommon for many to keep their central vision.
There are three major types of Usher syndrome; types I, II, and III. The types are further subtyped based on genetic causes. These types are distinguished by their severity and the age when signs and symptoms appear. The types are further divided into subtypes based on their genetic cause.
Most individuals with Usher syndrome type I are born with severe to profound hearing loss with vision loss identified in early childhood. Balance issues are a problem and children with Usher syndrome walk later than others.
Individuals with Usher syndrome type II have hearing loss from birth and progressive vision loss that begins later in life (adolescence or adulthood). Individuals with type II will complain that they can't hear soft sounds (like found in the letters t and d) and high sounds. Balance is typically not an issue with Usher syndrome type II.
People with Usher syndrome type III experience hearing loss and vision loss beginning somewhat later in life. Hearing loss typically begins during late childhood or adolescence, after the development of speech, and becomes more severe over time. By middle age, most affected individuals have significant hearing loss. Vision loss develops in late childhood or adolescence. Some people with Usher syndrome type III have vestibular abnormalities that cause problems with balance.