Glaucoma Drainage

Devices

Dr. Meenank

M. S. Ophthalmology ( Post- Graduate)

ASRAM

Introduction

Glaucoma – Multifactorial progressive optic neuropathy associated with visual field loss and characteristic structural changes, including thinning of the retinal nerve fibre layer and excavation of the optic nerve head Elevated IOP is clearly the most frequent causative risk factor.

Choice of treatment is mainly Medical Therapy LASER Treatment Filtering Surgeries

Choice of treatment in Refractory Glaucoma's isGlaucoma Drainage Devices (GDD)

Glaucoma Drainage Devices

Glaucoma drainage devices create an alternate aqueous pathway from the anterior chamber to the sub-conjunctival bleb or the supra-choroidal space by channeling aqueous out through a tube Drainage Devices

Setons (Bristle) - Refers to solid shaft prevents wound apposition

Stunt (Tubular structure) - Fluid passes passively

Valve - Tubular structure for unidirectional flow

Setons may be thread, wire, hair place in the wound to drain aq. Along side the inserted material

Setons were unsuccessful as they were unable to maintain fistula patency

Indications

GDD were designed mainly to enhance trabeculectomy surgeries

Indication Trab. With adjuvant therapy failed

Young patients

NVG, uveitic glaucoma, refractive pediatric glaucoma, glaucoma in Aphakia, PPK, VRS, PRP

Sever conjunctival scarring

Hi

st

or

y 1912: The first translimbal glaucoma drainage device implanted by Zorab ;

device used silk thread to drain fluid

1969: Molteno announced that a large surface area is needed to disperse the aqueous beneath the conjunctiva.

He inserted a short acrylic tube attached to a thin acrylic plate. Most of the operations failed after the first 3-6 months because of plate exposure, tube erosion, and scar formation.

1976: First Molteno implant was introduced consisting of a long silicone tube attached to a large end plate placed 9-10 mm posterior to the limbus .

The implant, which offered no resistance to the outflow, often resulted in hypotony , flat ACs , and choroidal effusions.

1992: George Baerveldt discovered that increasing the surface area of the end plate(s) results in lower IOPs .

Baerveldt non-valved silicone tube attached to a large silicone plate with a surface area of 250 mm², 350 mm², 500 mm²

1993: Ahmed glaucoma valve (AGV) introduced by Mateen Ahmed

1997: Introduction of the Helies drainage device which uses an artificial meshwork of PTFE fibers

1998: Glaucoma Drainage Devices have been implanted in 2,980 patients

2001: FDA approved the AquaFlow ™ Collagen Glaucoma Drainage Device as an alternative treatment for open-angle glaucoma

Physiology

Basic design of drainage implant device shows Fibrous capsule around effects the formation of bleb Granulation leads to collagen capsule @ 1month and stable at

6mnth all over Show microcystic spaces for aq. Drainage

Silicon tube from A.C to disc/plate

Ridge- where tube is inserted.Dec. risk of obs. due to fibrous capsule

Large surface area for formation of bleb

Implants

Implants can be studied under 1. Type of plate2. Type of material3. Type of opening

Type of plate – of the available rigid and flexible plates the later causes less inflammation

Type of material

Most commonly used materials are Silicon

Baerveldt, Krupin, Ahmed Polypropylene

Ahmed, Molteno Hydroxylapatite Expandable polytetrafluoroethylene

Medical grade silicone Biocompatibility

Low tissue response to implantationOdourless Tasteless Resistant to bacterial growthDoes not stain or corrode other materials

High tensile strength (1500psi), good elongation (to 1250%) and flexibility

Temperature Resistant Stable at a temperature range of 75-500oC

Chemical Resistant Resists water, oxidizing chemicals, ammonia, and isopropyl

alcohol

Polypropylene High flexibility and dimensional stability Low thrombogenicity Poor abrasion resistance Non-toxic High tensile and compression strength Chemically resistant to most alkalis and acids, organic

solvents, degreasing agents, and electrolytic attack Degrades in presence of UV light

Polytetrafluoroethylene or PTFE Chemically inert to most chemicals including nitric, sulfuric,

and phosphoric acids Hydrophobic Highly crystalline and stable Low friction Low wear resistance Inflammation caused by PTFE wear particles

Type of opening

Based on the type of opening implants can be classified into 1. Non- valved

Rely on resistance formed by fibrous capsule or bleb Bleb grows around the implant and creates a space for fluid

to drain and be absorbed by surrounding tissue Eg – Molteno, Baerveldt, Schocket

1. ValvedOnly drains fluid at a certain IOPValve opens and fluid is drained into a reservoir where it is

absorbed by surrounding tissues Eg – krupin, Ahmed

Non- valved devices

Baerveldt Implant Plate features

barium impregnated

Large surface area – 250 mm², 350 mm²(less complication), 500mm²(not available)

Location Superior- temporal quadrant under the sup. rectus muscle

inserted thgh one quadrant conjunctival insertion

Fenestration seen on the plate to allow fibrous capsule formation and dec.ht. of bleb and diplopia

Indication – failed Trabeculectomy, cataract Sx Side effects – restricted ocular movements @ 7yrs

Uncontrolled, complicated glaucoma

Molteno (1969) Original design –

Single acrylic thin plate ( 13 mm diameter & 135 mm² S.A)

Silicon tube (outer-0.62 mm , inner-0.30 mm) connected to upper end of plate

Thickened rim facilitating suturing to sclera adjacent to limbus

With subsequent modification came Single plate

Moved to a position a few millimetres away from limbus to allow for better drainage.

Aphakia, PPK, failed filters, NVG, < 3yr – 25% to 40%

Double plate Inc. S.A. 270 mm,

Better control but inc. complication – hypotony

Dual chamber In view to combat hypotony

Single implant ‘V’ shaped pressure ridge on upper surface of plate – inc. S.A. –10.5mm

Molteno 3 ( 175mm² & 230 mm²) Shows a bowel shaped structure on the implant plate at the tube opening

Acts a biological valve limiting aq. Flow during low aq. production

Schocket Tube Anterior Chamber Tube Shunt To Encircling Band ( ACTSEB)

Contains a silastic tube used in nasolacrimal intubation encircling at the equator under the rectus band

Show max IOP effect when coupled with krapin

Flow-Restricted Drainage Devices / Valved

Ahmed Glaucoma Valve (AGV)

Most commonly used valved implant

Implant design – silicon tube connected to silicon sheathed valve held by a polypropylene body

Material Surface Area Type

SiliconFP7 1.9mm² Single valve plateFP8 96 mm² Small valve plate FX1 180mm² 2 plates

PolypropyleneS2 189mm² Single valve plateS3 96 mm² Small valve plate B1 180mm² 2 plates

Valve related obstruction may cause hypertensive phase @ 4th – 8th P.O weeks

Hypertensive Phase : elevated IOP in the weeks to months after implantation as a result of capsule formation around the implant plate. This is frequently termed the hypertensive phase

Hypertensive phase is a result of holding the implant at no touch zone

No touch zone : area on the implant covering the silicon leaflet which when grasped with forceps separated the valve from implant – definitive closure –early P.O hypotony, fibro-vascular ingrowth b/w leaflet and implant failure

Krupin Implants (1976) Krupin and associates developed a concept of a valve that opens at a

predetermined IOP to dec. early P.O. complication Krupin Denver valve ( Original)

Internal supramid tube cemented to external silastic tube

Valve effect – by making a slit at closed ext. end of silastic which open opens at 9 – 10 mmHg IOP

Failure – no ext plate, and fibrosis eventually closed the valve

Krupin eye valve with disc Longer version of Denver and attached to Schocket 180 implant which open at 10 – 12

mmHg IOP and valve @ in side the rim of plate

Other Drainage Devices

Ex-PRESS Miniature non-valved device without an external plate

Made of rigid 316LVM stainless steel – same as cardiac stents

< 3mm long

Internal lumen size – 50µm/200µm

Biocompatible

Allows for the development of a delimited potential space and the formation of a fibrous capsule to create the resistance to outflow

Implanted under a traditional trabeculectomy flap

The Solx Gold Shunt Made from 24-karat gold and works to connect the anterior chamber and

suprachoroidal space

Pressure in the suprachoroidal space serves as a natural counter pressure to prevent severe postoperative hypotony

Implanted by using an ab external approach so, no bleb

iStent trabecular microbypass stent Stainless-steel stent with a lumen that is implanted from an ab interno approach

Traverses the trabecular meshwork and drains aqueous from the anterior chamber into the Schlemms canal, enhancing aqueous drainage

SURGICAL TECHNIQUES

Basic Principal

1) Proper Traction – achieved by 6-0 vicryl / silk through superficial cornea at superior limbus

2) Exposure Of Scleral Bed – a fornix based conjunctival flap is created and elevated by a blunt dissection b/w tenons and episcleral with blunt Westcott scissors exposing the scleral bed which is supported by relaxing incision for surgical exposure In case of large / double plate avoid superior-nasal ?

Can cause strabismus & close to optic nerve

3) Isolation Of Recti – muscle hooks are used to isolate the 2 recti on either side of the surgical site

Implant External implant is tucked under sub-tenons and sutured to sclera with 9-0 Proline

thgh the holes in the implant with the ant. Border 8-10 mm from limbus

2 stage implantation for non-valved Ext plate is inserted sub-conj without inserting the tube, which is done 6-8 wks after

fibrous capsule formation

(Or)

Occluding the tube with ligature before inserting it and checking with BSS for occlusion ( prevents P.O hypotony)

Entering into A.C.

With hemostasis achieved a pracentisis ia done @ for placement of visco-elastic

Tube is cut beveled up and to a distance of 2-3cm into A.C

Closure Autologous scleral graft of 5*7mm is used to cover the limbus and conjunctiva is

sutured followed by sub conj. Steroid and Antibiotic

COMPLICATIONS

Hypotony m.c complication with non- valved in early P.O days until fibrous capsule

formation

Rx – temporary obs of lumen

Basic tech – suture ligation of tube

Valve implants

Hypotony + flat A.C – Inject visco elastic – observe for 24hrs – no change – reposition device to prevent corneal decompensation

Late hypotony – Rx permenet occlusion of proximal tube and replacement of implant

Elevated IOP ( early / late ) Early – Before the ligature around the suture dissolves – transient ↑ IOP

Rx – medically / combine trab. Without MMC to control IOP

htn phase (7 – 8 days ) –↓ IOP conj & corneal oedema, cong⁺ around implant

HTN phase – IOP ass with fibrous capsule formation and ↓ oedema – bleb formation

1 – 4 wks – bleb cong⁺ ↑IOP - cong⁺ ↓IOP – stabiles

↑IOP due to tube obs – fibrin, blood, iris, vitreous membranes, or silicone oil Rx – reopening tube with – Iridectomy / NdYAG membrenctomy

Distal tube occlusion – scleral buckling Rx – BSS irrigation / intra-cameral Tissue Plasminogen Activator to dissolve fibrin clot

Late ↑IOP Seen with patent tube in thickened fibrous capsule

Rx – needle revision ;

complication – endophthalmitis

Migration, Extrusion, and Erosion If not adequately secured

Migrate post. In to A.C – Rx)- reposition and re suture with 9-0 Proline

Ant Migration is due to dislocation

Extrusion – m.c in pediatric cases due to the development of eye ball

Can cause erosion of cornea

Avulsion – causes corneal melting and requires explantation of the implant and possibly corneal grafting

Endophthalmitis commonly seen after needling procedure

Cause – Propionibacterium acnes endophthalmitis

Rx – vancomycin (poor response)

Explantation with new devise instillation is a must

Corneal Decompensation Related to the retrograde flow from the encapsulated reservoir to the

anterior chamber & Tube-cornea touch

Diplopia and Ocular Motility devices with larger plates, implanted in the superonasal quadrant, can

interrupt extraocular muscle function and cause strabismus and diplopia (exotropia, hypertropia, or limitation of ocular rotations )

Rx)- repositioning the device to superior-nasal

Other complication

Epidermal down growth With tube inserted at limbus –

implant failure, corneal decompensation

Sterile hypopyon After removal of suture stents in

eyes with silicon oil

Irregular pupil Root of iris adherent to tube

Globe penetration during suturing Cause – RD, Vit Hx

Retinal Complications RD, choroidal effusion,

suprachoroidal Hx ( old age, HTN, C. effusion, atherosclerosis)

Vision loss Hypotony, shallow A.C., RD, Vit

Hx, CME