There are three general types of Usher syndrome, each with varying degrees of severity in relation to hearing, vision, and balance:
|Type 1||Type 2||Type 3|
|Hearing||Severe deafness in both ears from birth||Moderate to severe hearing loss from birth usually in higher frequencies||No hearing loss at birth, but slow loss of hearing starting in childhood or teens|
|Vision||Slow vision loss starts with loss of night vision usually in childhood||Slow vision loss starts with loss of night vision in late childhood or teens||Timing and severity of vision loss vary, but most often night vision loss begins in teens|
|Balance||Balance problems from birth||No balance problems||Minimal to no balance problems at birth, symptoms may get worse with age|
Based on a table created by the US National Institute on Deafness and Other Communication Disorders (NIDCD).
In general, parents of children with Usher syndrome often notice signs of limited hearing first, usually in the first few years of life. At this stage, vision loss is likely not apparent, though it may be possible to detect subtle changes with vision testing. When vision loss beings to be apparent, the first signs are the same as those in other forms of RP: first, the loss of night vision, followed by compromised peripheral vision and a gradual narrowing of one’s visual field.
Early hearing loss can be detected and diagnosed with standard audiologic testing, which determines what frequencies of sound a child can hear, as well as how loud the sounds must be at these frequencies before they are audible. Children who are deaf or diagnosed with hearing loss can be screened for Usher syndrome in the following ways:
- ERG (electroretinography): this is a test that measures the electrical responses of the retina to light, evaluating responses of both rod and cone photoreceptors. The ERG test involves staying in a darkened room for 30 minutes, with drops put into the eye or eyes being tested. A special contact lens or gold-foil electrode is then placed on the eye or lower eyelid, and the eye is exposed to flashes of light.
- Visual field test: this exam is designed to detect, measure, and monitor blind spots in vision. It involves looking into a device that emits flashes of light, with the patient asked to indicate which flashes can be seen. The flashes that are not seen are recorded. This gives a measure of how much vision is affected.
- OCT (optical coherence tomography): this is an imaging technique that involves taking digital images of the various layers of the retina. The process uses light rather than sound or radio waves, which is why the images are in high resolution.
- Balance tests: these can be used to measure a child’s balance and clarify the diagnosis.
Genetic counselling: while not a test in the traditional diagnostic sense, genetic counselling is an important part of the diagnostic process. It can help determine the gene or genes that have been mutated, as well as the hereditary factors that are involved.