What is the ideal conjunctival bleb? Learning from minimally invasive glaucoma filtration surgery


Dao-Yi Yu

Stephen J. Cringle

William H. Morgan

Er-Ning Su

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Purpose: We ask the question: what is the ideal conjunctival bleb following glaucoma filtration surgery? We
reviewed our data from preclinical and clinical studies which used a new form of minimally invasive glaucoma surgery, a modified form of which (the Xen Gel Stent) is now in widespread clinical use.
Methods: The preclinical studies involved the implantation of gelatin microfistula tubes into 168 rabbits
and 34 monkeys. The follow-up periods extended out to more than two years in rabbits and six years in monkeys. Drainage from the blebs was monitored following anterior chamber injection of fluorescein. Clinical data from the subsequent clinical trial was also reviewed. Our new form of minimally invasive glaucoma surgery provides a great opportunity to study on the mechanisms by which aqueous humor drains from the bleb after glaucoma filtration surgery (GFS).
Results: Long-term drainage was monitored experimentally in both rabbits and monkeys. Essentially, aqueous
humor enters the subconjunctival tissue, joins the interstitial fluid, and forms the conjunctival bleb. In the bleb, there are close communications between aqueous humor and the structural molecules of the interstitial or the extracellular matrix, the blood and lymphatic vessels and parenchymal cells. The presence of conjunctival lymphatic drainage was a key determinant of drainage longevity. We have identified in long term of aqueous drainage (more than 6 years for monkeys and 2.4 years for rabbits), the initial lymphatic vessels are very close to the aqueous exiting point outside of the sclera. The clinical studies suggest that a diffuse flat bleb produced the optimum outcome. The mechanisms to re-establish balance of interstitial fluid in the subconjunctival tissue by which aqueous humor drains from the bleb after GFS have not been fully elucidated.
Conclusions: It is proposed that efficient conjunctival lymphatic drainage of aqueous from the bleb is a
key parameter for longevity of bleb drainage. Minimal disruption of the conjunctiva and the formation of a flat diffuse bleb appears to be optimal. Non-invasive methods of examining the conjunctival lymphatics are proposed.

Glaucoma Research 2018-2020, pp. 313-321 #22
Edited by: John R. Samples and Paul A. Knepper
© Kugler Publications, Amsterdam, The Netherlands

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