How common are inherited retinal degenerations?
Retinal degenerations affect men and women of all ages, races, cultures, and ethnic backgrounds. The broad range of retinal degenerative diseases affects at least six million Americans.
Approximately 100,000 people in the United States are affected by retinitis pigmentosa or Usher syndrome, which is a variation of RP that also impairs hearing. It is estimated that one of every 80 people carries a recessive gene for RP, although this does not mean they or their children will necessarily have the disease. Approximately six million Americans are diagnosed with age related macular degeneration, a disease that causes a loss of central vision. In addition, there are a number of less common forms of retinal degeneration.
What are the odds that I will pass the RP gene on to my children?
“Deciding whether or not to have children is a personal decision that everyone with RP has to make, and it is not an easy one,” says Diane Ryan, who has RP. (She is also Tom Tarrant’s mother.) Although she did not know her own diagnosis until after her children were born, she has shared her sons’ struggles with the decision of whether to take the risk of passing an RP gene to their offspring.
You can get the best information about the likely inheritance pattern of the disease in your own family by consulting with a genetic counselor or eye care professional who specializes in hereditary retinal degenerations. They can help you learn how the disease is inherited in your family and the chance of passing it on to your children.
What are the symptoms of RP?
Tom Tarrant: “I don’t ever remember seeing in the dark. I just don’t know what that’s like. I remember Halloween when I was a little boy, walking into poles.”
RP symptoms can vary. In a person with classic or typical RP, night vision and peripheral (or side) vision will be affected initially. Night blindness is one of the earliest and most frequent symptoms of RP, and it refers to difficulty seeing not only at night but also in dimly lit places, such as restaurants and movie theaters. The loss of peripheral vision is often called “tunnel vision.” If you imagine peering down a tunnel, able only to see what is in front of you and nothing to the side, this is what it is like to lose peripheral vision. As vision loss progresses, the “tunnel” becomes more and more narrow. In the later stages, some patients may also lose central vision.
Some cases of RP do not follow the classic symptoms of the disease. These patients may instead first experience some loss of central vision and color perception followed by night blindness.
What is common to all cases of RP is the progressive nature of the disease. When symptoms first appear they may be virtually imperceptible, particularly in an individual who is not aware of a family history of RP and thus not as observant of symptoms as an individual who has watched the disease develop in other family members. But symptoms may progress at different rates even in members of the same family. Once one adjusts to low vision, further adjustments will likely be necessary as the progression continues.