Assessment and monitoring of intracranial pressure (ICP) changes are important in the management of cerebral pathologies. In the eye, ICP increase and decrease both correlate with optic neuropathies, the former because of papilledema and the latter related to glaucoma. While the relationship between ICP elevation and papilledema is well established, the relationship between low ICP and glaucoma is still poorly understood. So far, ICP monitoring is performed invasively, but this entails risks including infection, spurring the study of non-invasive alternatives. While none of currently methods in use can fully replace invasive techniques, certain measures show great potential for specific applications. In this context, monitoring the intracranial pressure changes of normal tension glaucoma may lead to a better understanding of how intracranial pressure waves vary in normal tension glaucoma. Treatment of normal tension glaucoma as a two-pressure disease needs periodic intracranial dynamic monitoring sessions for evaluation of treatment effectiveness and for needed corrections of treatment methodology.

Project aim is to be able to monitor the "missing link" of intracranial dynamics of patients with normal tension glaucoma according to circadian rhythm: in the morning, during lunch and in the evening. The opportunity to monitor ICP waves non-invasively for patients with normal tension glaucoma will be implemented for the first time by using novel non-invasive intracranial pressure waves real-time monitoring system invented by KTU team in 2022 (patent applications are in the process of registration in the EU and USA).

Inclusion Criteria:

• 25-65 years of age.
• The patient, after reading the personal information form, confirms in writing his / her consent to participate in the study.
• The study group includes patients with a primary open-angle normal intraocular pressure glaucoma diagnosis confirmed by an ophthalmologist (typical glaucomatous changes in the optic nerve disc and eye area, open angle of the anterior chamber, intraocular pressure in the diurnal curve with/without anti-glaucoma medication ≤ 21 mmHg) and IOP ≤ 21mmHg on study day with/without anti-glaucoma medication.
• The control group includes healthy volunteers who do not suffer from glaucoma, acute or chronic uncompensated disease that may affect the results of the research, and according to age and anthropometric data correspond to the individuals of other research groups.

Exclusion Criteria:

• Patient's refusal to participate in biomedical research.
• Persons younger than 25 years or older than 65 years.
• A woman who may become pregnant, be pregnant or breastfeeding.
• The patient is allergic or sensitive to local anesthetics.
• Suffering from an eye disease that may distort the results of the study, if so decided by the examining physician.
• Patients who have had orbital or eye trauma.
• Patients who have undergone any eye surgery.
• Patients with acute or chronic, but currently aggravated, respiratory system disease.
• Patients with uncompensated cardiovascular diseases (II-III AV block or cardiogenic shock).
• Patients with uncompensated diabetes.
• Neurological diseases, mental illnesses identified in the anamnesis.

The study will include patients treated at the Clinic of Eye Diseases, Hospital of Lithuanian UHS.