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If an individual has a hearing loss, and Usher syndrome is suspected, there are several tests used to determine whether that individual has retinitis pigmentosa (RP). Some types of screening can be completed by a parent, teacher or other interested adult.
Some tests can be completed by most eye specialists during a regular exam:
Visual Field Test
Measures side vision using a machine called a Goldman Perimeter. It will indicate the field of vision (normal field=180 degrees).
Psycho-Physical Test
Indicates which colors, if any, an individual can distinguish and the amount of contrast needed to see.
Dark Adaptation Test
Determines an individual's ability to see in the dark and how long it takes to adjust to the dark.
Elctroretinogram (ERG)
The definitive test for RP, however, is the the electroretinogram (ERG), which has been found to be 95 percent accurate. The test must be administered by an opthalmologist. An ERG measures the elecricity given off by nerve impulses in the retina of the eye. The patient sits in a dark room until the eyes adjust to the darkness. One eye is then patched and the other fitted wtih a special contact lens. The test, which is painless, measures the elecrtical response of the uncovered eye as it is exposed to a flashing light.
Electronystagmography (ENG)
This test is considered the “gold standard” for diagnosing ear disorders affecting one ear at a time. This test is used to determine whether or not an individual’s dizziness or vertigo is caused by inner ear disease. This test involves carefully measuring the eye’s involuntary movements while the individual’s balance is stimulated in a variety of ways. The test is composed of four separate parts: (1) the calibration test, which will assess rapid eye movements, (2) the tracking test, which will assess the eye’s movements as it tracks a visual target, (3) the positional test, which will measure dizziness depending on the posture of the head, and (4) the caloric test, which will measure the ear’s response to varying temperatures of water run through the ear in small tubes.
USMChip
Dr. Kimberling at the Boys Town National Research Hospital has developed a microchip that will test saliva for all known types of Usher Syndrome. The microchip checks for 420 known DNA mutations and has a success rate of approximately 65-75%. The testing involves purchasing the microchip and sending a saliva sample by mail. Test results can take up to four months to be returned. The price of the test is approximately $200. For more information contact: Dr. Kimberling at National Center for the Study and Treatment of Usher Syndrome * Boys Town National Research Hospital * 555 N. 30th St. * Omaha, NE 68313 or call (402) 498-6713 or email him at kimber@boystown.org.
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