Ocular blood flow has been consistently demonstrated to be altered in glaucoma patients when compared to otherwise healthy individuals. Numerous Doppler studies have shown a decrease in flow velocities in the retrobulbar arteries in what appears to be related to the degree of the glaucomatous disease.

The anatomic pathway of the several arteries into the eye is intricately complicate, with at least one of them (the central retina artery) penetrating the optic nerve before entering the eye and supplying the innermost structures of the globe. As the optic nerve is surrounded by a layer of cerebrospinal fluid (CSF) which is in continuity with the rest of the central nervous system, this central retinal artery has also to cross this CSF containing compartment. Because of the intrinsic pressure this CSF - corresponding to the intracranial pressure at the orbital level - the possibility exists that this pressure around the optic disc could affect the blood flow of the arteries that go through it.

The investigators will try to detect if a correlation exists between the optic nerve sheath diameter and the blood flow in the retrobulbar vessels of glaucoma patients.

1. Visual field testing will be performed.
2. Structural analysis of the retinal nerve fiber layer (through confocal microscopy)will be performed.
3. Color Doppler Imaging of the retrobulbar vessels will be performed. Peak and end diastolic velocities, resistivity index will be calculated from the Doppler waveform.
4. B-scan ultrasound of the optic nerve sheath diameter will be performed. the measure will take place at 3mm behind the globe.

Inclusion Criteria:

• individuals over 18 years old
• willing to sign an informed consent and able to comply with the requirements of the study
• having no other ocular diseases besides glaucoma

Exclusion Criteria:

• history of ocular trauma
• intraocular surgery (except for cataract surgery)
• eye disease (except glaucoma)
• systemic diseases with ocular involvement like diabetes

primary clinic care