• Hirotaka Tanabe, Shunsuke Nakakura, and Hitoshi Tabuchi.
• Department of Ophthalmology, Tsukazaki Hospital, Himeji, Hyogo.
• Medicine (Baltimore). 2021 Jul 9; 100 (27): e26603e26603.

RationaleThe amount of aqueous humor that is constantly produced by the ciliary processes and the equal amount that flows out through the trabecular meshwork via the drainage angle or through the uveoscleral route is very small (2-3 μg/min each), representing approximately 1% of the content of the anterior chamber; therefore, it is challenging to visualize its flow.Patient ConcernsA 69-year-old man who had high intraocular pressure (IOP) (>20 mm Hg) with the maximum glaucoma eyedrop dose and presented with severe visual field loss (Humphrey Field Analyzer 30-2: -26.32 dB) had been implanted with a 350-mm2 Baerveldt tube of the aqueous chamber type for refractory open-angle glaucoma. The IOP ultimately decreased (<15 mm Hg) with no need for glaucoma eyedrops.DiagnosesAfter the procedures, a fibrin membrane repeatedly formed on the anterior surface of the intraocular lens.InterventionsThis issue was resolved by two rounds of neodymium-doped yttrium aluminum granet (Nd:YAG) laser surgery and prescription steroidal eyedrops.OutcomesDuring the laser surgery, an unusual and unintended fibrin flap appeared at the opening of the Baerveldt tube; this flap moved synchronously with the heartbeat, as verified by checking the pulse at the radial artery of the wrist. The fibrin flap mimicked the behavior of a cardiac valve, and the aqueous humor and stray fibrin particles mimicked the blood in the chambers of the heart. Although the Baerveldt tube itself is an artificial instrument that is not present in normal human eyes, we hypothesize that our observation shows the fundamental mechanism of aqueous humor drainage.LessonsThis novel, vividly descriptive observation highlights the important role of the heartbeat as a drainage pump in aqueous humor flow dynamics and IOP homeostasis, which are treatment targets for glaucoma, the leading cause of blindness.Copyright © 2021 the Author(s). Published by Wolters Kluwer Health, Inc.

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