A goniotomy is a surgery used to treat some forms of infantile/congenital glaucoma. The surgery was first portrayed in 1938. The surgery helps lower intraocular pressure (IOP) by making incisions into the trabecular meshwork to create a new opening that eases aqueous humour drainage into the Schlemm's canal.
Goniotomy is the most common surgery performed to treat congenital glaucoma. Congenital glaucoma is caused when there is a birth defect in the development of some structures in the anterior eye. One of these structures is the ciliary body, which is responsible for producing the aqueous humour. Instead, the structures overlap and block the trabecular meshwork responsible for the outflow of aqueous humour. Thus, the trabecular meshwork hardens, and it's drainage holes narrow, obstructing the aqueous outflow. This means that there's excess aqueous humour, which results in high IOP, causing glaucoma.
Since congenital glaucoma is found in children, parents are the ones who will notice the signs. The child will have teary eyes (epiphora), sensitivity to light (photophobia) and tends to shut their eyes for long periods (blepharospasm). At the eye specialist's office, the doctor conducts a full eye examination with the child under sedation, to ascertain its presence.
The earlier the procedure is done, the higher the success rate. When the child is less than two years of age, the success rate is between 90-94%. If the procedure is done on a newborn younger than one month old, the success rate is 25%.
Goniotomy is often done when there is no corneal clouding. In case the cornea is hazy, goniotomy is not recommended as the surgeon will not be able to clearly see the anterior structures. In this case, the following alternative glaucoma surgeries may be performed:
- Trabeculotomy - Here, the surgeon uses a probe to tear a hole in the trabecular meshwork.
- Placement of a filtering shunt to help with the outflow of aqueous humor. It is considered a good alternative when Schlemm's canal cannot be easily located, like in infants.
- Cyclodestructive techniques such as cyclophotocoagulation and cyclocryotherapy. These techniques use lasers or freezing temperatures to destroy the ciliary body. It is used when all other glaucoma surgeries have failed. They have a low success rate and high chances of developing complications.
Apart from treating congenital glaucoma, the procedure can also be used in the treatment of the following eye disorders:
- Maternal rubella syndrome
- Aniridia - A condition where the patient doesn't have a visible iris
- Uveitic glaucoma associated with juvenile rheumatoid arthritis
There are two ways goniotomy can be carried out:
- Surgical goniotomy
- Laser goniotomy (gonio photoablation)
Before the Procedure
A few days before the surgery, the child will be required to take medication that will lower the IOP and increase the cornea's clarity. The child will also take antibiotics for several days before the surgery.
Before the procedure is done, the parents or legal guardians are required to give their consent.
In the beginning, the patient is given miotics, which work by tightening the trabecular meshwork causing the pupil to contract. This allows the ophthalmologist to see and access the trabecular meshwork. The surgeon then administers medication that helps lower the patient's IOP. The patient is then anesthetized.
The ophthalmologist stabilizes the eye by using forceps and rotates the head away to see into the eye's interior structures easily. Using a goniotomy knife, the surgeon makes an opening in the cornea. To carefully do this, s/he looks into the interior eye through a microscope. As the specialist leads the technique, an assistant introduces fluid into the anterior chamber.
A gonioscope is positioned on the eye. The surgeon then moves the blade through 90–120 degrees of the eye's arc. As s/he is doing this, s/he will be opening the anterior trabecular meshwork, without interfering with the posterior trabecular meshwork, reducing the possibility of harm to the iris and lens.
The surgeon then removes the knife and passes a saline solution through the new opening and then closes it with sutures. S/he then applies corticosteroids and antibiotics to help manage inflammation and stop any possible infection. The patient's head is rotated away from the incision site to prevent blood accumulation. This procedure takes 20 minutes to complete.
If the other eye also needs a goniotomy, it can be operated on right after.
Risks & Complications
Due to the use of anesthesia, the patient can develop a reaction to it. Infants can react to anesthesia and develop cardiorespiratory arrest. However, this is rare (2% of goniotomies) and non life-threatening. Some side effects that the patient may experience include excessive tearing, sensitivity to light, and involuntary eye twitching. These will naturally disappear on their own.
Possible postoperative complications include:
- Hyphema - This is the most common complication arising from goniotomies. It is the bleeding and blood clot formation in the anterior chamber. This complication goes away in a few days.
- Hypotony - This a low IOP of 5mm/Hg and below caused when the eye's integrity is compromised, and there is insufficient aqueous humor.
- Lens dislocation - This complication increases if the patient is aniridic.
- Retinal detachment
- Cornea scarring
- Cataract formation
- Inflammation of the anterior chamber
Aftercare & Recovery
The patient will be given corticosteroids and antibiotics to use for a week or two after the surgery. The eye specialist might also prescribe medication to help lower IOP.
The patient will need periodic eye exams for the rest of their lives.
After three to six weeks, the patient will be anesthetized again for the reevaluation of the anterior chamber. The surgery is considered successful when:
- The measured IOP is below 21 mm/Hg
- There is no increase in corneal diameter. The ideal corneal diameter is 14mm and below. Since conducting a visual field test on a young child is difficult, the doctor measures the cornea's diameter to assess whether the glaucoma is progressing.
- Damage to the optic nerve is reversed or stabilized.
As the child gets older, this reevaluation can be done as a follow-up procedure that does not require sedation.
The child may require eyeglasses, which they should start using as early as possible to reduce the probability of developing amblyopia, a common disorder in pediatric glaucoma patients. Medicine that controls glaucoma may still be needed after goniotomy to control pressure in the eyes.
In about 10% of the patients, the condition recurs in the same eye or the unaffected one. This could be due to complications arising from goniotomy. When this happens, the procedure may be repeated. However, if it is not successful after three attempts, the surgeon will opt to perform a trabeculotomy.