As a specialist in the field of circadian rhythm disorders, I can provide an in-depth explanation of Non-24-Hour Sleep-Wake Disorder (Non-24) and its impact on both blind and sighted individuals.

Non-24 is a rare circadian rhythm disorder characterized by a disrupted sleep-wake cycle that does not align with the conventional 24-hour day. This misalignment can lead to difficulty falling asleep and waking up at the same times each day, resulting in a pattern of delayed sleep onset and wake times that progressively shift later each day, known as a "free-running" circadian rhythm.

### Prevalence and Risk Factors

While Non-24 is more commonly associated with individuals who are totally blind, it is not exclusive to them. The prevalence of Non-24 among the blind population is estimated to be over 50% due to the absence of light perception, which is a critical factor in entraining (synchronizing) the circadian rhythm with the environment. However, sighted individuals can also suffer from Non-24, albeit less frequently. The underlying causes in sighted individuals are often different and can include genetic predispositions, certain medical conditions, or the use of certain medications that affect the circadian rhythm.

### Clinical Presentation

The clinical presentation of Non-24 in sighted individuals is similar to that in the blind. Affected individuals may experience:

- Insomnia: Difficulty falling asleep due to the misalignment of the sleep-wake cycle with societal norms.
- Excessive Daytime Sleepiness (EDS): Feeling overly tired during the day, which can impact daily functioning.
- Social Rhythm Disruption: The inability to maintain regular social and work schedules due to the shifting sleep-wake times.
- Mood Disorders: The chronic sleep disruption can lead to increased risk of depression and anxiety.

### Diagnosis

Diagnosing Non-24 in sighted individuals involves a thorough medical history, sleep diary analysis, and possibly actigraphy—a method that uses a device to monitor rest-activity patterns over time. Additionally, a polysomnogram (a sleep study) may be conducted to rule out other sleep disorders.

### Treatment

Treatment for Non-24 in both blind and sighted individuals aims to align the circadian rhythm with the 24-hour day. Strategies include:

- Light Therapy: While light therapy is a cornerstone treatment for blind individuals, sighted individuals can benefit from controlled exposure to bright light at specific times to help reset their circadian rhythm.
- Melatonin: The timing of melatonin administration can be adjusted to help shift the sleep-wake cycle.
- Social Rhythm Therapy: This involves maintaining a regular schedule for sleep, meals, and social activities to reinforce a consistent circadian rhythm.
- **Cognitive Behavioral Therapy for Insomnia** (CBT-I): A structured program that addresses behaviors and thoughts that contribute to sleep problems.

### Conclusion

Non-24 is a complex disorder that can affect both blind and sighted individuals, although the prevalence and underlying causes may differ. A multidisciplinary approach involving sleep specialists, ophthalmologists, and mental health professionals is often necessary to manage the condition effectively. It is crucial for individuals experiencing symptoms of Non-24 to seek medical advice for proper diagnosis and treatment.

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No. While Non-24 is believed to affect over half of all totally blind individuals, it does affect some sighted people as well. However, the underlying causes are different, and these should be seen as two distinct disorders: Blind Non-24 and Sighted Non-24.Jul 15, 2017read more >>