Trabeculectomy

Trabeculectomy
Trabeculectomy, first described by Carain in 1980 is
the most frequently performed partial thickness
filtering surgery till date.
Indications
1. Primary angle-closure glaucoma with peripheral
anterior synechial involving more than half of the
angle.
2. Primary open-angle glaucoma not controlled with
medical treatment.
3. Congenital and developmental glaucomas where
trabeculotomy and goniotomy fail.
4. Secondary glaucomas where medical therapy is
not effective.
Mechnanisms of filtration
1. A new channel (fistula) is created around the
margin of scleral flap, through which aqueous
flows from anterior chamber into the
subconjunctival space.
2. If the tissue is dissected posterior to the scleral
spur, a cyclodialysis may be produced leading to
increased uveoscleral outflow.
3. When trabeculectomy was introduced, it was
thought that aqueous flows through the cut ends
of Schlemm’s canal. However, now it is established
that this mechanism has a negligible role.
Sugical technique of trabeculectomy (Fig. 9.23)
1. Initial steps of anaesthesia, cleansing, draping,
exposure of eyeball and fixation with superior
rectus suture are similar to cataract operation
(see page 187).
2. Conjunctival flap (Fig. 9.23A). A fornix-based or
limbal-based conjunctival flap is fashioned and
the underlying sclera is exposed. The Tenon’s
capsule is cleared away using a Tooke’s knife,
and haemostasis is achieved with cautery.
3. Scleral flap (Fig. 9.23B). A partial thickness
(usually half) limbal-based scleral flap of 5 mm ×
5 mm size is reflected down towards the cornea.
4. Excision of trabecular tissue (Fig. 9.23B): A
narrow strip (4 mm × 2 mm) of the exposed deeper
sclera near the cornea containing the canal of
Schlemm and trabecular meshwork is excised.
5. Peripheral iridectomy (Fig. 9.23C). is performed
at 12 O’clock position with de Wecker’s scissors.
6. Closure. The scleral flap is replaced and 10-0
nylon sutures are applied. Then the conjunctival
flap is reposited and sutured with two interrupted
sutures (in case of fornix-based flap) or
continuous suture (in case of limbal-based flap)
(Fig. 9.23D).
7. Subconjunctival injections of dexamethasone and
gentamicin are given.
8. Patching. Eye is patched with a sterile eye pad
and sticking plaster or a bandage.Complications
A few common complications are postoperative
shallow anterior chamber, hyphaema, iritis, cataract
due to accidental injury to the lens, and
endophthalmitis (not very common).
Use of antimetabolites with trabeculectomy
It is recommended that antimetabolites should be used
for wound modulation, when any of the following
risk factors for the failure of conventional
trabeculectomy are present :
1. Previous failed filtration surgery.
2. Glaucoma-in-aphakia.
3. Certain secondary glaucomas e.g. inflammatory
glaucoma, post-traumatic angle recession
glaucoma, neovascular glaucoma and glaucomas
associated with ICE syndrome.
Fig. 9.23. Technique of trabeculectomy: A, fornix-based
conjunctival flap; B & C, partial thickness scleral flap and
excision of trabecular tissue; D, peripheral iridectomy and
closure of scleral flap; E, closure of conjunctival flap.
4. Patients treated with topical antiglaucoma
medications (particularly sympathomimetics) for
over three years.
5. Chronic cicatrizing conjunctival inflammation.
Antimetabolite agents. Either 5-fluorouracil (5-FU)
or mitomycin-C can be used. Mitomycin-C is only
used at the time of surgery. A sponge soaked in 0.02%
(2 mg in 10 ml) solution of mitomycin-C is placed at
the site of filtration between the scleral and Tenon’s
capsule for 2 minutes, followed by a thorough
irrigation with balanced salt solution.