The Effect of Graded Forced Expiration on Intraocular Pressure

Intraocular pressure (IOP) is a key physiological parameter and the primary modifiable risk factor for glaucoma. Its dynamic nature is well-documented, with fluctuations known to occur due to a variety of factors, including posture, time of day, and bodily maneuvers. The Valsalva maneuver-forced exhalation against a closed glottis-is a classic example of a physiological stressor that can cause a transient, sharp increase in IOP. This occurs due to a rise in intrathoracic and episcleral venous pressure, impeding the outflow of aqueous humor.

While the effect of a maximal Valsalva is recognized, the quantitative relationship between graded levels of expiratory force and IOP remains poorly characterized. Previous studies have been limited by the inability to precisely control and measure respiratory effort, often relying on voluntary maneuvers that lack standardization and reproducibility.

The recent advent of portable respiratory muscle trainers, such as the Airofit device, offers a novel solution to this methodological challenge. This device enables the precise application of controlled, graded resistance to expiration across multiple predefined levels.

Therefore, the primary objective of this study is to utilize the Airofit device to systematically measure and characterize the changes in intraocular pressure across its six different levels of forced expiration. This investigation will provide crucial quantitative data on the IOP-respiratory effort relationship, enhancing our understanding of IOP dynamics during controlled respiratory stress and establishing a new, standardized paradigm for such research.

Methods

Study Design: A prospective, cross-sectional, single-visit study designed to measure the acute effect of a standardized respiratory exercise session on intraocular pressure (IOP).

Participants and Recruitment

A convenience sample of 60 adult participants will be recruited from outpatient clinics of physical medicine and rehabilitation of Usak university

Participants will be provided with a full information sheet and will sign a written informed consent form prior to any study procedures.

Inclusion criteria

• Aged 18 years or older.
• Willing and able to provide informed consent.
• Have a best-corrected visual acuity of 6/12 or better.
• Able to understand and follow instructions for using the Airofit device.
• Have an optic nerve cup/disc ratio not exceeding 0.5, and have a c/d difference between both eyes not exceeding 0.2.
• Did not have taken any anticholinergic medication, systemic beta-blockers, or corticosteroids within the last 3 months that could affect intraocular pressure levels.

Exclusion criteria

• a history of intraocular surgery,
• a history of uveitis,
• a spherical refractive error exceeding 3D,
• a history of regular topical treatment other than artificial tears