23.12.2025 It doesn’t hurt, it doesn’t sting, and most of the time it shows no warning signs at all. Yet, it can quietly impair vision. Intraocular pressure (IOP) is one of those parameters that seem insignificant – until you truly understand it. A new international publication explains that behind the simple number displayed by a tonometer lies a much more complex story.
One of the key parts of “Roadmap on advances in visual and physiological optics,” published in the Journal of Optics, is a chapter dedicated to intraocular pressure (IOP). This section was written by Dr. Karol Karnowski, head of the Image-guided Devices for Ophthalmic Care (IDoc) division at the International Centre for Translational Eye Research (ICTER), in collaboration with Bartłomiej J. Kałużny and Ireneusz Grulkowski from Nicolaus Copernicus University.
“Roadmap” papers are prestigious, authoritative reviews authored by researchers invited to define the current status and future directions of their field. The contribution from the ICTER team highlights one of the most fundamental yet overlooked parameters of the human eye.
The pressure that keeps the eye in shape
Intraocular pressure acts like an internal scaffold for the eye. It maintains the spherical shape of the eyeball, stabilizes the curvature of the cornea and sclera, and allows the optical system of the eye to function as it should. Under normal conditions, IOP typically ranges between 10 and 21 mmHg and results from a delicate balance between the production and outflow of aqueous humor.
When that balance is disturbed, the consequences are severe. Elevated IOP is the primary risk factor for glaucoma – a disease that often progresses silently, and it is still one of the leading causes of irreversible blindness worldwide. Pressure that is too low is also harmful; the eye loses its mechanical support, the cornea may become irregular, and the retinal image can be distorted.
Re-thinking the “Fixed Number”
One of the strongest messages in Dr. Karnowski’s chapter is the rejection of the idea that IOP is a fixed value. In reality, intraocular pressure is constantly changing to some extent, with every blink, every rapid eye movement, and every heartbeat. Besides the moment to moment variations, there are diurnal fluctuations, changes related to body position, and responses to physical effort.
A healthy eye can accommodate these fluctuations. The cornea-sclera-limbus system functions as an adaptive, self-regulating structure that protects visual quality despite momentary pressure changes. Problems arise when these mechanisms fail – under chronically elevated IOP, or in cases of significant hypotony. Consequently, mechanical changes begin to affect ocular optics, image quality, and ultimately the optic nerve itself.
Measuring IOP: still an imperfect art
Although intraocular pressure is routinely measured in ophthalmology clinics, the authors note that it remains an indirect measurement influenced by many variables. Corneal thickness and curvature, hydration, biomechanical properties, and even the phase of the cardiac cycle can all affect the result.
Goldmann applanation, Pascal dynamic contour tonometry, rebound tonometry, air-puff devices are all used to assess IOP; however, each of these tools measures something slightly different as a surrogate of IOP. It is therefore no surprise that the different instruments can yield different values for the same patient. This ambiguity complicates everyday clinical practice, long-term disease monitoring, and comparisons among centers.
Instead of isolated single time-point measurements, the future increasingly portends approaches that would capture multiple determinations of IOP over time; such as, home self-tonometry, smart contact lenses, and implantable microsensors. These technologies could reveal what single clinic visits may miss; e.g., night-time pressure spikes or short-lived mechanical overloads of the eye.
In addition, advanced eye models are being developed that combine biomechanics with optics. They incorporate not only pressure itself, but also tissue compliance, blood flow, and the optical consequences of mechanical changes. This approach is particularly important in refractive surgery and myopia research, where subtle biomechanical differences can have long-term effects.
More than a number on a chart
The chapter authored by Dr. Karnowski and his colleagues shows that documenting intraocular pressure is no longer just a box to tick during an eye exam. IOP is a dynamic component of a complex system that connects physics, biology, and medicine. And this is exactly how it is now being studied and described – broadly, yet with great precision – in the most influential international publications.
This publication also marks another milestone in the long-standing collaboration between ICTER and Nicolaus Copernicus University. By effectively bridging the gap between advanced optical engineering and clinical ophthalmology, this partnership continues to deliver critical insights into how the eye truly functions.
