Does the blood-brain barrier play a role in Glaucoma?

Area of Science:

• Neuroscience
• Ophthalmology
• Vascular Biology

Background:

• The optic nerve head (ONH) lacks a classical blood-brain barrier (BBB).
• Elschnig's tissue incompletely separates the ONH from fenestrated choriocapillaries.
• ONH microvessels have regional BBB variations, with weaker barriers in the prelaminar region.

Purpose of the Study:

• To investigate the implications of the incomplete blood-brain barrier in the optic nerve head.
• To explore the role of circulating molecules, like endothelin-1 (ET-1), in ONH vascular dysfunction.
• To understand the mechanisms leading to optic disk hemorrhages.

Main Methods:

• The study focuses on the physiological and pathological characteristics of the ONH blood-brain barrier.
• It examines the access of circulating molecules to ONH vascular cells.
• It discusses the impact of ET-1 and matrix-metalloproteinase-9 (MMP-9) on barrier integrity.

Main Results:

• Incomplete BBB in the ONH allows direct access of circulating molecules (e.g., ET-1) to vascular smooth muscle cells and pericytes.
• This access can cause vasoconstriction in peripapillary retinal vessels, potentially leading to retinal vein occlusion.
• ET-1 and MMP-9 can degrade the ONH barrier, allowing macromolecules and red blood cells to cross, causing optic disk hemorrhages.

Conclusions:

• The optic nerve head's compromised blood-brain barrier is susceptible to circulating vasoactive substances.
• Glaucoma may exacerbate ONH BBB defects, contributing to vascular pathologies.
• ONH barrier breakdown can lead to significant clinical manifestations like optic disk hemorrhages.