The retina is the innermost coating of the eye, containing light-sensitive nerve cells and fibers connecting with the brain through the optic nerve. The retina is held in place by the pressure of a gel (vitreous) within the eye.
In order to understand how some retinal diseases are inherited, it is important to be aware of the following patterns of inheritance:
Inherited from one affected parent, with a 50% chance of each pregnancy being affected.
Inherited from both non-affected parents, with a 25% chance of each pregnancy being affected.
Inherited from a non-affected mother, with a 50% chance of each pregnancy being affected. Usually only sons are affected.
An ERG (electroretinogram) may be used to diagnose certain retinal diseases. Testing involved objective measurement of the retina’s response to a light stimulus under well-controlled environmental lighting circumstances. In most cases, testing takes place under normal lighting conditions as well as in the dark. In order to perform the ERG test, usually young infants need to be sedated.
The pupils of the eye will be dilated and eyelids propped open. Contact lenses are placed on the eyes in order to provide the flash stimulus. Recording electrodes are taped to the scalp. The test requires a couple of hours to be completed. the ERG provides information to establish the appropriate diagnosis. It does not provide measurements that necessarily predict visual function. When performed on an infant, test results may be inconclusive. requiring retesting when the child is older.
Additional information is available in the Blind Children’s Center Pediatric Visual Diagnosis Fact Sheets.