BLINDNESS AND SLEEP

AND SLEEP

HOW INABILITY TO SEE CAN AFFECT SLEEP/WAKE CYCLES

W R I T T E N B Y S E T H W A L L A C E , M D

PATIENT SCENARIO

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S C H E D U L E . It seems like it takes longer and longer for him to fall asleep with each night that passes, and he feels like he needs to sleep in later and later. His sleep/wake periods will become progressively more delayed, such that after nearly a month, his sleep schedule will have delayed hour by hour until he is right back where he started.

DISCUSSION

Question: Is blindness the culprit in this patient? Why does this happen?

Blindness is the cause of the progressive delay in the patient’ s sleep schedule. To get an idea of what is going on, let’ s first look at some basics with the internal clock in the brain. It is often referred to as the circadian clock. The prefix “ circa ” means around, and the suffix “dian ” means day, so circadian literally means around the day. Our circadian clock isn ’t exactly 24 hours; it is a bit longer, closer to 25 hours. If you had a watch that ran fast, you would have to set it back occasionally to keep it on schedule. Because our internal clocks “ run fast, ” we have to have a way to synchronize our clocks as the earth rotates once every 24 hours.

Can you think of a good cue that tells our brains when a new day begins a particular location on earth? How about the rising of the sun? Is it possible that somehow our internal clocks can be synchronized by the rising of the sun? Here is what normally happens. Light enters the eye and causes a photochemical reaction in pigments in the retina. This reaction is kind of like flipping a switch, and electrical signals are passed down the optic nerve and on to the back of the brain, where they are processed.

There is a tiny part of the brain behind the eyes that sits next to the optic nerves called the suprachiasmotic nucleus (SCN). The SCN monitors how much traffic is going through the optic nerves. At night, there is little activity going through the optic nerves. With morning, electric impulses start cruising down in the optic nerves, and the SCN figures it must be daytime and synchronizes itself.

In our patient, the SCN isn ’t getting the signals through the optic nerves that synchronize it with the world around it, so the patient’ s clock tells him to wake up about an hour later each day.

Question: Does this daily sleep delay happen to all blind people?

Let’ s pose some scenarios and see what we can determine. Let’ s say that the patient has horrible focus and can ’t make out any detail because everything is so blurry. Would there be the same progressively delayed sleep schedule? No, because light is still causing activity in the optic nerve. How about if a person had a stroke which wiped out vision processing at the back of the brain resulting in blindness? If the eyes are working and the optic nerve is transmitting, the SCN still gets the word that there is light and synchronization occurs, even though that person may not be able to see.

TREATMENT

Stimulating melatonin receptors is another way to signal the body that time for sleep is approaching. Melatonin is produced by the pineal gland which sits near the SCN. Melatonin production is suppressed by light, but as light decreases, levels of melatonin in the bloodstream rise. The melatonin helps regulate the circadian clock. Oral melatonin, or a new prescription medication (tasimelteon), stimulate melatonin receptors and help regulate the sleep/wake cycle.

Problems related to the circadian clock are fascinating. If you desire to learn more, you might want to research some other disorders related to the circadian clock, including delayed sleep phase disorder, advanced sleep phase disorder, shiftwork sleep disorder, and jet-lag.

S&W

Dr. Seth Wallace is a native of Utah. He earned an undergraduate degree from Weber State University and received his MD from Tulane University in New Orleans. He is board-certified in sleep medicine and family medicine. Dr. Wallace is also interested in aviation and aviation medicine. He is an FAA-designated aviation medical examiner and an instrument-rated private pilot. Dr. Wallace resides in South Jordan, Utah.