Molecular Genetics of Retinal Degenerations

This multinational study will investigate the inheritance of genetic retinal degeneration in
families of different nationalities and ethnic backgrounds in order to identify the genes
that, when altered, cause retinal degeneration. The retina is a light-sensitive membrane
lining the back part of the eye. It relays vision signals to the brain, which the brain
interprets into sight. When the retina degenerates, vision is altered and possibly lost. The
findings of this study should help improve diagnosis and methods of treatment for these
disorders. Participating institutions include: the National Institutes for Health in
Bethesda, Maryland; the University of Miami in Florida; the Casey Eye Institute in Portland,
Oregon; the Byrd Health Sciences Center in Morgantown, West Virginia; the University of Texas
Southwestern Medical School in Dallas, Texas; the University of Tennessee Health Sciences
Center in Memphis; the Prasad Eye Institute in Hyderabad, India; National Center of
Excellence in Molecular Biology in Lahore, Pakistan; and the Jules Gonin Hospital in
Lausanne, Switzerland.

Patients with retinitis pigmentosa and closely related diseases such as Usher syndrome,
snowflake vitreoretinal dystrophy and Bietti crystalline dystrophy may be eligible for this
study. Participants undergo the following tests and procedures:

- Medical and surgical history, including family history of vision problems.

- Examination to clarify the type of retinal degeneration.

- Eye examination, including tests of color vision, field of vision and ability to see in
the dark

- Electroretinogram to test the function of visual cells. For this test, the patient sits
in a dark room for 30 minutes with his or her eyes patched. Then, a small electrode
(silver disk) is taped to the forehead and the eye patches are removed. The surface the
eyes is numbed with eye drops, and contact lenses are placed on the eyes. The patient
looks inside a large dark globe that emits a series of light flashes. Then a light is
turned on inside the globe and more lights flash. The contact lenses sense small
electrical signals generated by the retina when the light flashes.

- Hearing tests for patients with a personal or family history of deafness. Tests include
an audiogram, ear examination and test of middle ear function. For middle ear function
testing, the patient feels a little air pressure change for a moment and hears some
tones. Another test requires the patient to sit quietly with electrodes on the head,
forehead and earlobes.

- Balance testing, including walking in a straight line, standing with eyes closed in the
dark and other tests of coordination, and caloric testing. For the caloric testing, any
ear wax in the ear canal is removed before the test begins. Then, electrodes are placed
on the skin near the eyes and on the forehead. A small amount of cool (sometimes cold)
or warm water is instilled into each ear canal, first one and then the other.

- Blood sample collection for genetic testing.