In addition to intraocular pressure blood perfusion pressure in the optic nerve is an important factor determing the cause of glaucoma. Increasing evidence suggests that in glaucoma patients retinal blood may be decreased.

According to the World Health Organization (WHO) glaucoma is the second leading cause of blindness. Glaucoma is a global problem, which is becoming even more important as the human life expectancy increases. Although the causes of glaucoma are uncertain, mainly intraocular pression (IOP), genetics, and ocular blood perfusion pressure in the optic nerve determine the cause of the disease. Increasing evidence suggests that in glaucoma patients retinal blood flow is decreased leading to progression and to damage of the optic nerve.

In order to measure the peripapillary blood flow a variety of devices using different techniques of flowmetry have been developed. In this study, the reproducibility of the retinal flowmetry measured with the LSFG-NAVI device from Nidek will be investigated. A high reproducibility is crucial for the clinical value of any measuring device.

Inclusion Criteria:

• signed Patient Informed Consent form
• Be at least 18 years old
• Diagnosis of primary or secondary open-angle glaucoma or normal tension glaucoma or healthy controls

Exclusion Criteria:

• Age < 18 years
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc. of the participant.
• No vulnerable participants will be included in this study.

3 groups as described above will be recruted from the outpatient department of the Ophthalmology Department at the UniversityHospital Zurich, Zurich, Switzerland and the Ophthalmology Department at the Cantonal Hospital Aarau, Aarau, Switzerland