GONIOTOMY

 

INTRODUCTION:

Goniotomy (Gk. gonio—angle and tomein—to cut) is a procedure to open the angle of the anterior chamber by an ab interno technique. The operation was popularized by Otto Barkan in 1938, following development of the gonioscope. The procedure did not do well in adults as it led to scarring of the angle and subsequent failure of the surgery. Barkan utilized it for congenital glaucoma, where it proved relatively successful, compared to the bleak prognosis conventionally associated with this group of diseases.

The steps of the procedure have largely remained unchanged, a testament to the success of the technique.

Barkan surmised that an abnormal membrane (Barkan membrane) obstructed the angle. And goniotomy opens a route for aqueous humor to egress out of the eye through the Schlemm’s canal by removing the tissue obstructing the angle. However, it is now believed that the incision is not through a membrane, but rather through the inner portion of the trabecular meshwork. This presumably relieves the compressive traction of the anterior uvea on the meshwork and eliminates any resistance imposed by incompletely developed inner meshwork. In any case, successful goniotomy does appear, however, to reduce the IOP by improving facility of aqueous outflow.

In cases of corneal opacification, endoscopic visualization has been utilized to open up the angle.

Recently, goniotomy techniques in adults have gained traction with the development of gonioscopy assisted transluminal trabeculotomy and the Kahook Dual Blade.  

https://ourgsc.blogspot.com/search?q=kahook 

INDICATIONS:

Goniotomy is most successful in the treatment of primary congenital glaucoma presenting between 3 and 12 months of age, but it may also be used in other primary developmental and secondary glaucomas, although with reduced success  rates.

Examples of these other primary glaucomas include juvenile open-angle glaucoma and early-onset glaucomas associated with Sturge-Weber syndrome, neurofibromatosis, and Lowe syndrome. Several secondary glaucomas may respond favorably to goniotomy in some cases, including glaucoma complicating chronic anterior uveitis and selected cases of aphakic glaucoma presenting early after congenital cataract surgery.

PRE-OPERATIVE PREPARATION:

Pharmacological therapy is given for a few days to reduce IOP, this may help in clearing the cornea. Medications include oral acetazolamide, topical dorzolamide, apraclonidine 0.5% and beta-blockers. Just prior to surgery the pupil is miosed to prevent inadvertent injury to the lens. This can be done by topical pilocarpine or intra-cameral miochol (Acetylcholine chloride 1:100).  Apraclonidine 0.5%, may be applied to the eye just before surgery and may help decrease intraoperative bleeding.

Topical hypertonic saline (Sodium chloride 5%) helps in clearing the corneal edema and improves visualization.

STEPS OF SURGERY:

1. A low profile wire speculum is preferred to avoid pressure on the globe.
2. The goniotomy lens (Barkan, Lister, Swan-Jacob, Hill or Khaw) is placed on a mound of viscoelastic on the cornea. The microscope is tilted approximately 45-degrees from the vertical. And the child’s head turned towards the surgical side. The patient's head is tilted 30-degrees away from the surgeon to have a proper view of the angle.
3. The globe is stabilized using locking forceps on the insertion of Tenon’s capsule.
4. The eye is entered through peripheral clear cornea 1 mm from the limbus, using a 25-gauge, 1.5-inch needle (goniotomy needle or knife). The knife/needle is kept parallel to the iris. Keeping the knife/needle above the iris, the anterior trabecular meshwork is entered.
5. An effective trabecular meshwork incision is made by keeping the incision superficial and into anterior trabecular meshwork, passing first in one direction, then the other; the assistant rotates the globe while the needle is not engaged in the meshwork.
6. Care should be taken to incise only the anterior third of the trabecular meshwork, just posterior to the Schwalbe’s line.
7. A circumferential incision is made for about 4 to 5 clock-hours.
8. A deeper cleft, with exposure of whiter tissue may be noted in the wake of the incision, with a widening of the angle, and a posterior movement of peripheral iris in some cases.
9. Remove the needle carefully over the iris and have the assistant “relax” any pull on locking forceps at this time.
10. The entry site should be quickly compressed with a cotton bud to minimize chamber collapse.
11. The anterior chamber is refilled with balanced salt and filtered air bubble.
12. The wound is closed with an absorbable 10-0 suture.

POST-OPEARTIVE TREATMENT:

Postoperative treatment includes the use of topical antibiotic, steroid, and miotic agents. (Miotics are often omitted, however, in cases of uveitic glaucoma.) The baby's head should be kept elevated (a car seat works well for this), and the eye should be shielded for 1 to 2 nights, until any hyphema has settled.

COMPLICATIONS:

Mild to moderate hyphemas commonly occur after goniotomy, but they almost always clear rapidly without sequelae over several days.

Other complications after goniotomy are rare and include iridodialysis, cyclodialysis, appearance of small peripheral anterior synechiae in the incised angle, damage to the crystalline lens, and retinal detachment in eyes with high myopia.

Occasionally, a significant amount of blood will reflux into the anterior chamber during the first 72 hours after surgery; when this becomes complicated by an elevated IOP, washout of the blood should be considered.

RESULTS:

The success of goniotomy in controlling glaucoma varies with the cause of the glaucoma. The best results—70% to more than 90% success after one to two procedures—are achieved in infants with primary congenital glaucoma presenting between 3 months and 1 year of age.

Success rates with goniotomy (and angle surgery in general) are much lower for cases of primary congenital-infantile glaucoma presenting at birth or after 12 months of age (success in these groups is usually about 30% to 50%).

Both immaturity of the juxtacanalicular meshwork and/or underdevelopment of Schlemm’s canal or collector channels could explain the failure of goniotomy.

CONCLUSION:

Goniotomy can prove an effective procedure for control of IOP in selected cases. The appeal of this conjunctiva sparing procedure makes it a worthwhile approach in the management of pediatric glaucoma, and is becoming increasingly popular for adult glaucomas.