Ahmed Glaucoma Valve Pf.박찬기/R2 유가영

Glaucoma drainage devices Tube + Reservoir plate Fibrous capsule forms filtering bleb around the plate Tube End plate

Glaucoma drainage devices 1907 Rollet Implant a horse’s hair Maintain patency of a drainage fistula Hair, wire, threads….. Fail because of excessive scar formation near the limbus

Glaucoma drainage devices 1969 Dr. Anthony Molteno Using large surface area to disperse aqueous near the limbus 1973 Drained the aqueous 8-10mm away from the limbus Molteno device

Implant Design Open-tube drainage devices Baerveldt, Molteno, Schocket implant Flow-restricted drainage devices Ahmed valve, Krupin valve implants Krupin Baerveldt Ahmed Molteno

Implant material Materials that prevent fibroblast adherence Polypropylene(may produce more inflammation) Some Ahmed, Molteno implants Silicone Baeveldt, Krupin, Ahmed device

Basic principles Goal ! Non-valved implants resulting hypotony !!! Remove aqueous out of the AC without causing hypotony Maintain long-term lower IOP Non-valved implants resulting hypotony !!!

Ahemd valve mechanism (1) Two silicone thin elastomer membranes 8mm long, 7mm wide Sandwiched and stretched by plates Elastomer: 탄성중합체

Ahemd valve mechanism (1) Self-regulated resistance One-way regulation of the flow when IOP is above 8~10mmHg Lowest rate of hypotony

Ahemd valve mechanism (2) Venturi design Overcome internal resistance in valve system helps in evacuating aqueous from the valve, thereby helping to reduce valve friction. Elastomer: 탄성중합체

Ahmed Glaucoma Valve Models Material Model Size Polypropylene S2 184mm² B1 364mm² S3(pediatric) 96mm² Silicone FP7 FX1 FP8(pediatric) FP-7 may lower IOP at 1yr more than S2

Prototype : model S2 Silicone tube Large polypropylene plate Plate Thickness : 1.9mm Width : 13.00mm Length : 16.00mm Surface area : 184mm² Tube Length : 25.00mm Inner diameter : 0.305mm Outer diameter : 0.635mm

Different biomaterials : model FP7 Silicone tube + Silicone plate Good biocompatibility 60% edge thickness Facilitate closure of conjunctiva Three holes Tissue growth through through the hole Increasing the effective area available for drainage Silicone may reduce inflammation and scarring during encapsulation of the device

Bi-plate : model B1 and FX1 Second plate(180mm²) Increase the size of end plate & surface area Greater aqueous drainage → lower IOP

Pediatric : model S3, FP8 Smaller in size Polypropylene Plate Width : 9.60mm Length : 10.00mm Surface area : 96.00mm² Tube Length : 25.00mm Inner diameter : 0.305mm Outer diameter : 0.635mm Polypropylene Silicone

Pars plana clip : model PC and PS Enter posterior chamber at sharp angle → kinking

Indications Young patients Failed trabeculectomy Neovascular glaucoma Uveitic glaucoma Severe conjunctival scarring Refractory pediatric glaucoma Aniridia

Contraindications There are no known absolute contraindications Borderline corneal endothelial function may worsen

Surgical technique Position Tube priming Superotemporal quadrant Superonasal quadrant Post. edge of the plate may be close to the optic nerve with further posterior placement of the plate Tube priming BSS must be irrigated through the tube using 27G cannula During sterilization process, membranes may adhere to each other → Ensure valve opens Air removal

Surgical technique “No touch zone” Creation of subconjunctival space in the superotemporal quadrant Fornix based Wet-field cautery in used sparingly(esp. around the tube insertion site) Insertion of plate into subconjunctival space using nontoothed forceps Avoid holding device over the valve body → May damage valve and fibrovascular ingrowth Ant. edge of valve : 8-10mm posterior to the limbus Suture with #8-0 or #9-0 nylon “No touch zone”

Surgical technique Cutting the tube to the appropriate length Bevel upward toward cornea Tube tip extend 2~4mm into AC Entering the AC through the limbal area with a 23G or 22G needle parallel to the iris plane Approximately 0.5mm posterior to the limbus

Surgical technique Tube insertion into the AC via the needle track using nontoothed forceps Should not touch cornea, iris, lens Posterior to schwalbe’s line and anterior to the iris plane Loosely secured to sclera, avoiding constriction of the tube Suturing of donor sclera or other patch material(pericardial tissue, fascia lata…) over the tube area at the limbus Prevent tube erosion

Surgical technique : modifications Viscoelastic Through paracentesis, temporally Maintain AC at normal depth SO filled eye Plate positions : inferotemporal Minimize SO loss through the tube Limbal based scleral flap Post vitrectomized eye Pars plana insertion prefered Eliminate tube-cornea touch Model PC and PS

Complications Hypotony Choroidal effustion Less common with Ahmed Glaucoma vlave

Complications All glaucoma drainage implants Obstruction of tube by fibrin, blood, iris, vitreous Tube retraction and erosion Tube kink Motility disturbance Corneal decompensation and graft failure Endophthalmitis Retinal detachment

Complications Elevated IOP Hypotensive phase(7-10days) low IOP, conj/corneal edema, conj. vessel cong. Hypertensive phase(1-4weeks) IOP elevation, capsule formation The incidence of the hypertensive phase may be lower after silicone plate(FP7) than polypropylene plate(S2) Stabilization(3-6month) Early IOP increase Tube obstruction by fibrin, blood, iris, vitreous membrane, silicone oil

Complications Failure of priming Fibrovascular ingrowth Uncommon Late failure Gap between valve chamber and plate during manipulation of the valve

Reference Shields textbook of GLAUCOMA 6th edition, ALLINGHAM Shaarawy GLAUCOMA surgical management, SAUNDERS Chen, Teresa C., Glaucoma surgery, SAUNDERS

감사합니다