Usher syndrome refers to a deaf-blindness condition. Patients with Usher syndrome have hearing loss and retinitis pigmentosa. RP is characterized by difficulty in balance, loss of peripheral vision, night blindness, retinal degeneration, and finally “tunnel vision”.Usher syndrome accounts for fifty percent of deafness and blindness cases. It occurs in 1 of 23,000 births in the US (Boughman, Vernon, & Shaver, 1983), and 1 in 12,500 in Germany (Otterstedde, Spandau, Blankenagel, Kimberling, & Reisser, 2001). Other countries have reported prevalence within this range. Usher syndrome is an inherited autosomal recessive disorder; symptoms of the syndrome may not be observable in a parent if he or she carries only a single copy of the gene. However, if both parents carry a copy of the gene, then there is a one in four chance that a child will get Usher syndrome. Nine genes have already been identified to cause Usher syndrome, although it is thought that many other genes could be responsible (Ebermann, et al., 2010).
These genes are responsible for encoding proteins that are involved in muscle function, cell adhesion, receptor function, synaptic shaping and scaffold formation (Williams, 2008). Clinically and genetically, the syndrome is heterogeneous resulting in three types of based on the onset and extent of deafness (National Institutes of Health, 2011). Type 1 individuals are deaf from birth and have poor sense of balance. Children with type 1 do not benefit from hearing aids, and efforts should be made to find the best means of communicating with them. It will become more difficult when blindness sets in. In Type 2 Usher syndrome, deafness is less severe, and motor skills are normal. Retinitis pigmentosa sets in during the teen years. Type 3 patients have mild but progressive deafness, with 50% of patients having dysfunctional balance or vestibular dysfunction. Progression of the disease varies, but blindness sets in during puberty and is complete by mid-adulthood (Williams, 2008; National Institutes of Health, 2011). Usher syndrome is diagnosed by evaluating vision, balance and hearing (National Institutes of Health, 2011). Vision is tested by conducting a field test to check the patient’s peripheral vision. An electroretinography is performed to test if the rods, cones and ganglions in the retina are still sensitive to light. In this procedure, an electrode is placed at the front of the eye to measure the response of the retinal cells to a light source. A light is flashed, and the response of the retina can be viewed on a computer screen. The pattern of the response is recorded in waves. Readings are taken under normal light and in the dark. Balance is tested with an electronystagmogram that measures involuntary eye movements (nystagmus). The latter test is conducted to check if connections among the nerves, ear and brain are working. Vertigo, dizziness, and loss of balance are symptoms that there are problems with these connections. In an electronystagmogram, electrodes are placed around the eyes (below, above and to the side). Another electrode is taped to the forehead. Cold water is then delivered to the ear canal, which should result in rapid side-to-side movement of the eyes. Then warm water is added, which should result in the eyes moving slowly towards the warm water and also slowly away. The electrode will measure the length and speed of the eye movements. Values below and above normal will indicate problems with the nerve connections. Hearing is tested by an aerologic test that measures the range that loud sounds at different frequencies can still be heard. The first step is to see if an audiogram is necessary by blocking one ear and checking the ability to hear different sounds. Tuning forks are also used. The fork is tapped and held at the side of the ear to test the ability to hear through conduction. Alternatively, earphones that are connected to an audiometer are worn by the patient. Tones are then delivered and the patient