Filtration Surgery and Antimetabolites in Glaucoma

Prof. Dr. R. K. Mishra.
(Rajendra Eye Hospital, Jabalpur)

Glaucoma Filtering surgery and role of Antimetabolites.

As a foreword, first, few words about the present status of Glaucoma Filtering procedures and use of Antimetabolites.

Cairn's trabeculectomy is still the most popular and durable amongst the filtering procedures.

Pressure-lowering effect of trabeculectomy is based on aqueous flow through the loosely closed edges of the scleral flap into the subconjunctival space and drained there after.

Causes and site of Failure in surgery

First, Scleral Fluid gate between the AC and bleb is closed. Reasons-iris block, lens block, inflammatory / fibroblastic membrane formation.
Second, sclerostomy created at the time of surgery is too small.
Third, Scaring in the filtration bed, Conjunctival suture line and the scleral flap gap

Identification of high risk failure cases

{a} Inflammatory condition.
{b} Neo visualization in the Anterior segment.
{c} Young age.
{d} Aphacik glaucoma.
{e} Previously failed filtration surgery.
Those at high risk include
{f} Some races of African origin.
{g} Uveitic glaucoma.
{h} Combined cataract and glaucoma surgery.
{i} Childhood glaucomas.

How this menace is to be tackled?

[1] Surgical planning for adequate filtration
[2] Use of drugs to prevent Undue Fibroblastic Response

Surgical planning

History of Keloid or Pemphigus, Trachoma, xerosis, operative scars and re-operations - extra care in planning for anti-inflammatory drug,
Select site carefully topical steroids to be planed in advance.
Iridectomy
Full thickness iridectomy extending beyond width of scleral window is crucial .In smaller iridectomy the iris root may block the scleral window.
Limbal based conjunctival flap - conjunctival and the tennon margins are sutured separately and meticulously in watertight manner.
Testing the passage
Through a pre made corneal paracentesis track inject BSS note fluid travel through the scleral gate to subconjunctival space. Watch the watertight ness of the conjunctival suture line.

Medical planning

[a] Steroids. Steroids work well within limits.
[b] Antimetabolites like 5.Flurourecil or Mitomycin C

Antimetabolites

To increase success rates of filtration surgery use of antimetabolites - help prevent growth of fibroblasts during the time the aqueous humor contains the stimulatory properties.

Antimetabolites are nonspecific. And not targeted solely at proliferating fibroblasts, they are equally effective against the normally replicating cells involved in ocular metabolism also.

5.Fluourocil

5-FU is more toxic to replicating cells than to non proliferating cells;

Route of Application

Subconj. Injection of 5-FU post operatively significantly improves success rate even in Aphakik patients for almost a year.

Dose & frequency

The optimal dose and frequency of 5-FU administration is yet to be determined. As of now 5mg a day for 7 days then 5,mg alternate days a total of 50mg in 10 injections.

Injection site

Injecting 5FU --The site for injection be placed in a healthy unscarred area well away from the site of surgery.
P.O.5.F.U. Injection

1st. Post operative Wk.5.mg daily 2nd. P.O.Week 5 mg alternate day. Total of 50. Mgs. in 10 injections.
Post5.F.U injection

A careful eye examination is necessary before each 5-FU dose including vision and Fundus

Mitomycin-C

MMC an antibiotic isolated from Streptomyces. Is used as adjunctive therapy to reduce fibrosis in trabeculectomy.

MMC Toxicity

Like 5-FU, Mitomycin is toxic to replicating cells and interferes with fibroblast proliferation. MMC is highly toxic to corneal endothelium but less so to the corneal epithelium.

Method to use MMC.

In books the dose recommended be 0.2 to 0.5mg per Ml. solution applied for 2 to 5 minutes. This concentration and contact time is not safe.

Books mention two options for placing the MMC. soaked sponge.[1] On the sclera after dissecting the conjunctiva and draping it over [2] on the floor of the scleral flap .

I use 0.133mg/ml sol .for 1 min. and on the floor of the flap rather than on the scleral surface it self.

Complication of 5FU injection

Epithelial toxicity. This can range from superficial punctuate keratopathy to large epithelial defects of the cornea, Corneal filaments may develop.

5FU. Toxicity

Epithelial defects created by 5-FU, with topical steroid in use, may be slow to heal and (rarely) can develop secondary infection

5.FU Toxicity

Shallow or flat anterior chamber, choroidal effusion hypotony with decreased vision has been reported after the use of 5- FU.

MMC. Complications

1. Wound leak
2. Thin bleb
3. Hypotony
4. CME.
5. Corneal ulceration
6. Scleral ulceration
7. Scleromalacia
8. Scleral calcification
9. Symblepharon.

MMC as the bad guy!

The bad name to MMC is more due to procedure followed than the drug toxicity. Between 5.F U and MMC my preference is for MMC. If the rules of the game are followed MMC is quite safe.