Imaging of the aqueous outflow with contrast-agend-based optical coherence tomography

Background

The eye continuously produces aqueous humor, wich delivers nutrients to the intraocular tissue and builts up a certain intraocular pressure to maintain good optical properties of the eye. Regulation of the intraocular pressure mainly occurs through the outflow resistance at the site of aqueous drainage in the chamber angle.  Dysfunction of the aqueous outflow regulation is considered the main factor leading to elevated intraocular pressure, which in turn is a major risk factor for the development of glaucoma. All established treatment strategies of glaucoma aim at reducing the intraocular pressure.

While the first site of outflow resistance called trabecular meshwork is relatively well characterised, the further downstream located drainage system of collector channels and intrasceleral aqueous veins remains a rather elusive part of the eye. Due to its complex structure, which is hidden deep in the scleral tissue little is known about its morphology and even less about its functional properties. However, with the recent trend towards novel microinvasive glaucoma surgery techniques targeting the trabecular meshwork, our lack of understanding the distal outflow pathway becomes increasingly relevant: In a significant number of cases opening the trabecular meshwork does not lead to a sustained drop of intraocular pressure. The currently available data suggests that a better knowledge about the distal outflow pathway would enable us to better target microincisional surgery and might, thus, increase the success rates of these surgical procedures.

Optical coherence tomography (OCT) provides high resolution cross sectional images of tissue and has become one of the most important diagnostic procedures in ophthalmology. OCT angiography (OCT-A) is a further development of OCT technology, which allows to selectively detect a signal derived from moving blood in blood vessels. Due to the monophasic nature of aqueous humor OCT-A does not per se work for aqueous veins.