National Sleep Foundation

Chapter 5: Circadian Rhythm Sleep Disorders

Prevalence

Who is affected by Non-24 Hour Sleep Wake Disorder?

Non-24 is primarily observed in completely blind individuals (i.e., those without any light perception), as their inability to perceive any light prevents them from synchronizing their internal body clock to the day-night cycle. About 10 percent of blind people in the United States lack light perception; of these individuals, as many as one-half to three-quarters are considered to have Non-24 — a total of about 65,000 to 95,000 Americans.54

The number of sighted persons who have the disorder is not known, although there are case reports of Non-24 in sighted individuals.

References 

54. National Sleep Foundation (NSF), Non-24 in Sighted vs. Blind, Arlington, VA: NSF, no date. Online at:  http://sleepfoundation.org/non-24/content/sighted-vs-blind.