How Sleep Apnea May Contribute to Normal-Tension Glaucoma Risk

People with obstructive sleep apnea syndrome (OSAS), a disorder characterized by repetitive episodes of paused and shallow breathing during sleep, are approximately ten times more likely to develop glaucoma. This is a well-known and well-documented relationship, but the underlying cause of this correlation has remained a mystery. Is there an increase in intraocular pressure (IOP) during these episodes of paused breathing, or is it something else altogether? May further research be a jumping off point for more potential explanations of normal-tension glaucoma?

OSAS correlates with various disorders, such as heart attack and ischemic stroke, causing researchers to wonder what, if anything, are the commonalities between these very different disorders. They hope that through better understanding of what occurs over the course of apnea episodes they can potentially translate this knowledge into glaucoma treatment. To continue to investigate this connection, researchers need to take numerous factors into account and use innovative, new technology to determine the real connection.

Creating Innovative Technology

Because increased IOP is most often associated with glaucoma, it is the first thing that researchers investigate when they see correlations with other disorders, such as OSAS. In the past, night-time data collection to search for the connection between OSAS and glaucoma was hampered, since it’s challenging and uncomfortable to collect data related to shifts in IOP while the patient is sleeping, and constant waking affects the accuracy of measurements of IOP flux over the course of the night.

Researchers recently developed an innovative contact lens to track intraocular pressure. The contact lens sensor (CLS) allows for round-the-clock monitoring of IOP without needing to wake you up or interrupt your daily/nightly routine. The lens shifts and responds to changes in corneal curvature and circumference, which relate to changes in IOP. As the curvature and circumference changes, there is an electrical change in the CLS, which is interpreted as an upward or downward shift in pressure. By using this new contact lens technology, researchers are hoping to gain new insight into obstructive sleep apnea by continuously monitoring the eye pressure even during sleep cycles.

Assessing the Connection Between Eye Pressure and Apnea Events

Using the contact lens sensor in conjunction with polysomnography—equipment used to track multiple factors of sleep—researchers are able to measure both apnea events and IOP simultaneously. Researchers hope to demonstrate that during apnea events there is spike in IOP, as pressure in the chest rises when people stop exhaling. The results, however, are quite the opposite of what they anticipated: apnea episodes are associated with a drop in IOP.

OSAS is still associated with glaucoma, but researchers have now realized that it isn’t due to an IOP increase or changes in chest pressure. Instead, it might be due to a drop in oxygen levels in the blood, which happens when you stop breathing. Routine low oxygen concentration in the blood may contribute to degradation of the optic nerve, potentially leading to glaucoma. As this appears to occur in apnea patients with glaucoma in the absence of a change in IOP, this revelation may provide insight into those with normal-tension glaucoma (NTG). This also could explain the correlation between OSAS, heart attacks and strokes: in all three cases, there is a prolonged period of oxygen deprivation.

Potential Normal-Tension Link

The causes of normal-tension glaucoma remain unknown, but new theories are emerging. Much like primary open-angle glaucoma, without regular trips to the eye doctor to check the optic nerve for signs of damage, it may go unnoticed until significant vision loss has occurred. Earlier diagnosis and better understanding of this form of glaucoma may help preserve sight.

With novel discoveries and new technology to implement in studies of this disease, researchers may be able to uncover the underlying triggers of all varieties of glaucoma. The more that researchers understand about this challenging disease, the more likely they are to find a cure.

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