An international team of researchers lead by Lithuanian experts adds to the growing body of data that intracranial pressure is important in normal-tension glaucoma, which accounts for up to 50% of all glaucoma cases. A recent clinical study discovered that low intracranial pressure is linked to impaired patient vision, particularly in the nose zone.
Optic nerve degeneration produces glaucoma, one of the main causes of blindness in persons over the age of 60. In glaucoma patients, increased pressure inside the eye (called intraocular pressure or IOP) is frequently noted. However, not everyone who has ocular hypertension develops glaucoma. Furthermore, glaucoma can develop in the presence of normal IOP.
According to several research, the prevalence of so-called normal tension glaucoma (NTG) among patients in the global population ranges from 30 to 90%. “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 KTU’s Health Telematics Science Institute, invented the non-invasive intracranial pressure measuring method employed in the study.
He goes on to explain that the optic nerve is anatomically connected to the brain and is surrounded by cerebrospinal fluid. Intracranial pressure (ICT), which is pressure within our skull measured in cerebrospinal fluid, and intraocular pressure (IOP) can both impact the optic nerve’s health. Recently, researchers have focused on the balance between the two pressures, known as translaminar pressure differential (TPD), and its relationship to the development of glaucoma.
A new study including 80 patients with early-stage normal tension glaucoma (NTG) was done by researchers from Lithuanian, Israeli, and American universities. Between January and October 2018, 300 NTG patients were sent to the Eye Clinic at the Lithuanian University of Health Sciences.
Several measures were taken throughout the investigation, including intraocular pressure (IOP), intracranial pressure (ICP), and visual field perimetry. TPD = IOP – ICP was used to compute the translaminar pressure differential (TPD). There were five zones in the visual field: nasal, temporal, peripheral, central, and paracentral.
The study found multiple statistically significant associations between intracranial pressure, TPD, and changes in visual field. The greater the TPD, the more substantial the impairment to the patient’s visual field. The nasal zone had the most substantial visual field reductions.
“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.
According to the researchers, greater TPD might be considered a risk factor for the detrimental development of normal tension glaucoma. Because TPD is computed by subtracting ICP from IOP, the lower the intracranial pressure reading, the greater the TPD. Thus, decreased intracranial pressure may be a risk factor in 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 link between intracranial pressure and glaucoma opens up new possibilities for medical practitioners to investigate the cause and potential therapy of this condition. In addition, data supporting this concept has come in from research organisations operating all around the world in recent years. Prof Ragauskas claims that his study has contributed to the expanding amount of data on the subject, both directly and indirectly.
The intracranial pressure was measured in the above-mentioned study using a two-depth Transcranial Doppler (Vittamed UAB, Lithuania) created by Prof Ragauskas’ team at the Kaunas University of Technology laboratories. Unlike the traditional method of monitoring intracranial pressure, which entails drilling a tiny hole into the patient’s skull, Prof Ragauskas’ innovation uses ultrasound to measure brain pressure non-invasively through the eye. The invention’s industrial uses were patented 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.
