A group of researchers, primarily from Lithuania, have provided further evidence indicating that intracranial pressure is a significant factor in normal-tension glaucoma, a form of glaucoma that constitutes up to half of all cases. The results of a recent clinical study show that reduced intracranial pressure is associated with decreased visibility in patients, particularly in the nasal area.
Glaucoma is a common cause of blindness for those over the age of 60, and it is characterized by damage to the optic nerve. Typically, glaucoma patients exhibit heightened pressure inside the eye, also known as intraocular pressure (IOP). However, not everyone with high IOP develops glaucoma. Conversely, glaucoma can also occur in individuals with normal IOP, a condition referred to as normal tension glaucoma (NTG). Studies suggest that NTG may affect between 30 and 90 percent of patients globally.
"Contemporary medicine has methods to treat elevated eye pressure and to slow or even stop the damage to the optic nerve. However, these methods do not work in the case of normal tension glaucoma. There is a growing awareness among the scientific community, that glaucoma is a condition caused by two pressures—inside the eye and the skull," says professor Arminas Ragauskas from Kaunas University of Technology (KTU), Lithuania.
Ragauskas, the Head of the Health Telematics Science Institute at KTU, is the inventor of the non-invasive intracranial pressure measurement technology, used in the study described below.
According to him, the optic nerve is connected to the brain and surrounded by cerebrospinal fluid, which can be affected by both intracranial pressure (ICT) and intraocular pressure (IOP). Researchers have recently examined the relationship between these pressures and the development of glaucoma, focusing on the balance between the two pressures, known as the translaminar pressure difference (TPD).
A group of researchers from universities in Lithuania, Israel, and the United States conducted a recent study involving 80 patients with early-stage normal tension glaucoma (NTG). The participants were chosen from the 300 NTG patients referred to the Eye Clinic at the Lithuanian University of Health Sciences between January and October 2018.
During the study, several measurements were taken, including intraocular pressure (IOP), intracranial pressure (ICP), and visual field perimetry. The translaminar pressure difference (TPD) was calculated using the formula TPD = IOP - ICP. The visual field was divided into five zones: nasal, temporal, peripheral, central, and paracentral.
The study found significant correlations between intracranial pressure, translaminar pressure difference (TPD), and changes in visual field among the 80 early-stage normal tension glaucoma patients. Higher TPD values were associated with more significant damage to the visual field, with the nasal zone being the most affected area. These correlations were statistically significant.
"Visual field loss means only one thing—a person is becoming blind. That's why it is so important to understand the causes of this condition and to reverse it. We are all aware of the dire outcome," says Prof Ragauskas.
Based on the study's findings, researchers have concluded that a higher translaminar pressure difference (TPD) may be considered a risk factor for negative development in normal tension glaucoma. Since TPD is calculated by subtracting intracranial pressure (ICP) from intraocular pressure (IOP), a lower measure of ICP leads to a higher TPD. Therefore, reduced intracranial pressure could potentially be a risk factor for normal tension glaucoma.
"The idea that brain pressure is related to the visual field is not new. Several years ago, we conducted a series of experiments studying the links between visual field and intracranial pressure, using the non-invasive technology developed here, at KTU. In the conferences that followed, I saw how our new idea was met with excitement by the international community of ophthalmologists," says Prof Ragauskas.
The correlation between intracranial pressure and glaucoma provides new opportunities for medical professionals to explore the causes and potential treatments for the disease. Research groups around the world have contributed evidence supporting this hypothesis in recent years. Professor Ragauskas, the inventor of the non-invasive intracranial pressure measurement technology, has directly and indirectly contributed to this growing body of data.
In the recent study, the team used a non-invasive intracranial pressure measurement device developed by Professor Ragauskas' team at Kaunas University of Technology. The device, called a two-depth Transcranial Doppler (Vittamed UAB, Lithuania), measures brain pressure through the eye using ultrasound, unlike the traditional method, which involves drilling a small hole in the patient's skull. The invention has been patented for various industrial applications in the United States and Europe.
"We are not competing with invasive methods, but heading towards an entirely new direction. At the moment, I see that ophthalmology is the field where our technology is needed most, and we are using it for research purposes. However, we are constantly developing our invention and have recently patented a couple of new applications, which might be used in other contexts where measuring intracranial pressure is crucial. For example, in long-term space missions," says KTU professor Ragauskas.
The findings are published in the journal Diagnostics.
Akvile Stoskuviene et al, The Relationship between Intracranial Pressure and Visual Field Zones in Normal-Tension Glaucoma Patients, Diagnostics (2023). DOI: 10.3390/diagnostics13020174