Eye pressure is an important risk factor for glaucoma, but scientists still do not fully understand what causes it to fluctuate throughout the day and night. Researchers at the University of South Florida (USF) have developed a wireless monitoring system that provides continuous measurements of eye pressure in rats, revealing previously difficult-to-observe links between pressure, the body's circadian rhythm and exposure to light.
The latest research, led by USF professor Christopher Passaglia with alumna Alexandra Zamitalo as lead author, was published in Investigative Ophthalmology & Visual Science. The work forms part of a series of three studies examining the biological mechanisms involved in regulating pressure inside the eye.
Monitoring pressure around the clock
In clinical practice, eye pressure is generally measured at a particular moment during an eye examination. However, intraocular pressure is not constant. It changes over a 24-hour period, including during sleep, when measurements are rarely performed. "No one was continuously measuring eye pressure until we figured out a way," Passaglia said. According to him, continuous monitoring has revealed patterns that were largely invisible with conventional measurements.
The system developed by the researchers uses a miniature pressure sensor connected to the eye of a rat through a small tube. It records pressure continuously while the animal carries out its normal activities. Rats were used because their daily eye-pressure rhythms show similarities to those observed in humans.
Measurements showed that eye pressure followed a daily rhythm and increased at night. The researchers found that this nighttime rise was driven by neural signals travelling from the brain to the eye. This suggests that intraocular pressure is partly regulated by the body's biological timing system rather than exclusively by mechanisms within the eye itself. The animals did not develop glaucoma despite experiencing nighttime pressure levels that, if continuously sustained, are associated with the disease. Why this occurs remains unclear.
Light disrupts the pressure rhythm
The researchers also investigated whether changes in the light-dark cycle could affect intraocular pressure. To disrupt the animals' normal circadian rhythm, they exposed them to constant light. The effect was stronger than expected. The normal daily rhythm in eye pressure disappeared, while average pressure began to increase.
The findings do not mean that ordinary exposure to artificial light causes glaucoma. The experiments were conducted in rats, and their results cannot be directly translated to humans. They do, however, provide further evidence of a connection between eye-pressure regulation and the body's circadian clock. This raises additional research questions about how disrupted biological rhythms may influence eye health over longer periods.
Glaucoma research
Elevated intraocular pressure is a major risk factor for glaucoma, a group of eye diseases that can progressively damage the optic nerve and lead to vision loss. Understanding how and why pressure changes over a 24-hour period could therefore provide additional insight into disease development and progression.
The USF research is focused primarily on understanding the underlying biology rather than introducing a new clinical diagnostic or treatment method. By identifying the neural pathways, chemical signals and tissues involved in controlling eye pressure, researchers hope to build a more complete picture of communication between the brain and the eye.
The findings could eventually also support research into whether the timing of glaucoma treatment influences its effectiveness. If eye pressure and the mechanisms controlling it vary throughout the day, some therapies could potentially have different effects depending on when they are administered.
For now, however, the work remains preclinical. Further research will be required to determine whether the mechanisms identified in rats also play comparable roles in humans and whether continuous monitoring can ultimately contribute to improved glaucoma prevention or treatment.
References
Investigative Ophthalmology & Visual Science (Research)
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