Total Blindness and Non-24 Sleep Disorder
Eye On the Cure Research News
Non-24 is a very rare condition affecting many (but not all) people who are totally blind and have absolutely no light perception. Their circadian clocks become out of sync as a result.
Recently, you may have been hearing and seeing commercials for a blindness-related sleep disorder called Non-24. In the radio ads I've heard, the narrator says he's totally blind and suffers from the condition. The media spots are sponsored by Vanda Pharmaceuticals, which recently received approval from the U.S. Food and Drug Administration for a drug called Hetlioz to treat Non-24.
The ads have piqued our curiosity at the Foundation Fighting Blindness. We've been wondering what Non-24 is, and who it affects. As an organization that funds research for retinal degenerative diseases — e.g., retinitis pigmentosa, Leber congenital amaurosis, Stargardt disease, age-related macular degeneration and choroideremia — we were especially interested to know if Non-24 affects people with these conditions.
So I spoke with sleep-disorder experts Steven W. Lockley, Ph.D., at Harvard, and Helene Emsellem, M.D., medical director at The Center for Sleep Disorders in Chevy Chase, Maryland. What they told me is that Non-24 is not likely to affect most people with retinal degenerative diseases. Here's more information on what I learned.
What is Non-24?
Our bodies (and brains) operate on a circadian clock, which regulates many biological systems, including sleeping and waking. For most people, the clock is approximately 24 hours and reset everyday by the first perception of light.
Dr. Emsellem says that Non-24 is a very rare condition affecting many (but not all) people who are totally blind and have absolutely no light perception. Their circadian clocks become out of sync as a result. Furthermore, their sleep-wake cycles often drift day to day by varying degrees. For example, if their cycle is drifting by 30 minutes, they may feel like going to sleep at midnight one day, 12:30 a.m. the next, and so on.
People with Non-24 have trouble going to sleep at night and staying awake during the day. The condition can wreak havoc on their lives, especially those in school, working or caring for a family. As if being totally blind in the sighted world wasn't difficult enough!
Why Most People with Retinal Degenerations are not at Risk
While many people with retinal degenerative diseases have severe vision loss and use accommodations such as navigational canes, guide dogs, talking computers and other high-tech gadgets, a vast majority maintain some level of light perception and are, therefore, not at risk for Non-24.
Even people who have lost all of their rods and cones to a retinal degenerative disease may not get Non-24. That's because the cells in the retina that regulate the circadian clock — photosensitive ganglion cells — usually survive after photoreceptors are gone. Even though a person with a retinal degeneration does not experience light perception, there is a good chance his or her photosensitive ganglion cells are still functioning and sending signals back to the brain to synchronize the person's circadian clock.
Who is at Risk of Non-24?
Researchers have found that people more likely to have Non-24 are those who have advanced conditions or diseases which affect retinal ganglion cells, and/or the optic nerve, which is the cable that sends signals from the retina back to the brain. As reported in the journal Sleep, these individuals can include people with: traumatic optic neuropathy, advanced retinopathy of prematurity, severe retinal detachment and retinoblastoma, a cancer of the retina which is sometimes treated by removal of the eyes.
Dr. Emsellem says that people with normal vision can have Non-24, but those cases are extremely rare, and scientists aren't sure why these individuals are affected.
Managing Sleep Disorders
Just because a blind or visually impaired person doesn't have Non-24 doesn't mean he or she doesn't have another sleep disorder that is or isn't related to vision loss. Lifestyle habits, such as diet, exercise and stress management, can all be affected by vision loss, and they significantly impact the quality and duration of sleep.
Dr. Emsellem reports that more than 50 million people in the United States have sleep disorders or are not satisfied with their alertness during the day. She provides helpful information on sleep disorders and getting a good night's rest on her website. She strongly encourages people to seek help from a sleep specialist for treatment of persistent sleep-alertness issues.