Computed tomography of aqueous humour outflow pathways

Area of Science:

• Ophthalmology
• Comparative Anatomy
• Medical Imaging

Background:

• The conventional and uveoscleral pathways are known routes for aqueous humor outflow.
• Understanding the dynamics of aqueous humor drainage is crucial for managing intraocular pressure (IOP).

Purpose of the Study:

• To investigate the distribution and clearance of a radio-opaque contrast medium perfused into the anterior chamber of Rhesus monkeys.
• To explore the role of ocular and orbital tissues in fluid dynamics and drainage.

Main Methods:

• Perfusion of the anterior chamber with Amipaque (a radio-opaque contrast medium) in adult Rhesus monkeys at controlled intraocular pressure (IOP).
• Utilizing computed tomography (CT) to examine the distribution of the contrast medium in vivo and post-mortem.
• Maintaining artificial IOP post-mortem to observe diffusion patterns.

Main Results:

• In living monkeys, the contrast medium remained confined to the anterior chamber even after 8 hours of perfusion.
• Post-mortem, with IOP artificially maintained, the contrast medium rapidly diffused into the anterior segment, orbital tissues, globe wall, and extraocular muscles.
• No contrast medium entered the vitreous body, and diffusion posterior to the extraocular muscles was limited.
• Elevated IOP did not appear to increase posterior diffusion rates.

Conclusions:

• In vivo, contrast medium entering posterior aqueous drainage pathways is likely cleared rapidly by blood circulation in the uvea and extraocular muscles.
• Tenon's capsule may act as a barrier, limiting further intra-orbital diffusion of substances from the anterior segment.