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Review
. 1998 Sep;82(9):1083-9.
doi: 10.1136/bjo.82.9.1083.

Glaucoma drainage devices; past, present, and future

K S Lim  1 , B D Allan, A W Lloyd, A Muir, P T Khaw
Affiliations
Review

Glaucoma drainage devices; past, present, and future

K S Lim et al. Br J Ophthalmol. 1998 Sep.
No abstract available

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Figures

Figure 1
Figure 1
(A) Single plate Molteno implant (scale bar = 1 cm). (B) Dual chamber double plate Molteno implant (scale bar = 1 cm). (C) Schematic drawing of the resistance mechanism of a dual chamber single plate Molteno implant. The thin V-shaped ridge (see B) has the same height as the circumferential rim of the polypropylene plate. The top surface of the plate is divided into one smaller and one larger chamber by the apposition of the overlying conjunctival and Tenon's layers (dotted line). Aqueous flows (black arrow) into the smaller proximal chamber until sufficient pressure is achieved within the chamber to lift (white arrow) the overlying conjunctival layer to allow free drainage.
Figure 2
Figure 2
(A) The Krupin valve with disc, slit valve is situated at the plate end of the tube (scale bar = 1 cm). (B) A schematic drawing of the Krupin slit valve, showing the crossed slit elements.
Figure 3
Figure 3
(A) The Baerveldt implant (scale bar = 1 cm). (B) Schematic drawing of the appositional resistance mechanism included in some embodiments of the Baerveldt GDD. An annular ridge projecting from the underside of the plate element provides a temporary seal against the sclera. Absorbable sutures are used to hold the plate in apposition. As the sutures degrade, the plate element lifts clear, allowing free aqueous drainage.
Figure 4
Figure 4
(A) The Ahmed glaucoma valve implant (scale bar = 1 cm). (B) Schematic drawing of the resistance mechanism of the Ahmed valve. Aqueous flows (black arrow) through the tube into a chamber within the plate element. This chamber is formed by a folded over silicone membrane (black line) with its free edges forming a one way valve. Manufacturers claim that the two halves of the polypropylene body of the plate element pre-tension the valve to open at a specific level of intraocular pressure. They also claim that the venturi effect produced by the tapering trapezoidal shape of the space enclosed by the folded silicone membrane acts to improve flow regulation (increasing fluid velocity as the chamber tapers acts to reduce internal pressure proximal to the slit opening in accordance with the inverse relation between fluid velocity and pressure expressed in the Bernoulli's theorem). Neither of these claims is supported by the published experimental evidence.
Figure 5
Figure 5
(A) The OptiMed implant is made up of a silicone tube with a PMMA plate. The "flow restricting" element of this device is housed within the rectangular box situated at the end of the tube within the plate (scale bar = 1 cm). (B) Schematic drawing of the OptiMed implant's "flow restricting" unit which is made up of multiple microtubules providing a pressure gradient governed by Poiseuille's formula.
See this image and copyright information in PMC

Comment in

  • Ex-PRESS implant.
    Mermoud A. Mermoud A. Br J Ophthalmol. 2005 Apr;89(4):396-7. doi: 10.1136/bjo.2004.061689. Br J Ophthalmol. 2005. PMID: 15774910 Free PMC article. No abstract available.

References

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    1. Eye (Lond). 1992;6 ( Pt 4):346-7 - PubMed

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