Fluctuations in intraocular pressure (IOP) during sleep are affected by a complex network of physiological changes, said JoAnn Giaconi, MD, at Glaucoma Subspecialty Day. This intricate web of circadian factors may influence glaucoma progression.
Although IOP is often assumed to rise at night due to postural changes, some people—including about half of those with normal-tension glaucoma—experience their lowest IOP at night. Scientists are teasing out the roles of circadian factors in nighttime IOP to understand how these changes contribute to glaucoma.
Many factors affect sleep physiology and IOP. “Sleep physiology is very complex. IOP at night may be more complex than it first seems,” said Dr. Giaconi. “And the way the two interact is going to be even more complex.”
Rather than waking patients during the night to measure IOP, which may distort data, some researchers are using contact lens sensors (such as Triggerfish) that are worn continuously. This approach reveals wide variations in nocturnal IOP from person to person, despite relatively predictable changes in brain waves, blood pressure, breathing patterns, and other physiological factors.
Blood pressure. Dr. Giaconi reviewed the current understanding of how these circadian factors and underlying health conditions influence IOP. Among these is blood pressure. On average, most people experience a 10% drop in blood pressure during sleep. This shift in blood pressure can interact with IOP to alter a person’s ocular perfusion pressure. “If blood pressure and IOP go in opposite directions, this can negatively affect perfusion of the nerve,” she said.
Intracranial pressure. Dr. Giaconi noted that intracranial pressure also interacts with IOP but does so in a less predictable way. A supine position decreases intracranial pressure, while slowed breathing increases it. A shift in either direction can interact with IOP to modulate translaminar pressure.
Sleep apnea and nocturnal IOP. Obstructive sleep apnea has been linked to glaucoma. Studies suggest a possible reason: Pharynx obstruction during periods of apnea can induce hypoxemia, stimulate the sympathetic response, and alter IOP.
Further study needed. Although IOP fluctuations normally occur during sleep, future work should explore whether such IOP changes affect optic nerves in general, or only those that are susceptible to glaucoma. Or perhaps abnormal nighttime physiology is to blame for optic nerve issues, said Dr. Giaconi, adding, “There are many things we still don’t know about IOP at night.”—Anni Griswold
Financial disclosures. New World Medical Inc: C.
Disclosure key. C = Consultant/Advisor; E = Employee; L = Speakers bureau; O = Equity owner; P = Patents/Royalty; S = Grant support.