Canaloplasty is a new, advanced, minimally invasive and non-penetrative surgical procedure used to treat open-angle glaucoma. The technique aids in the drainage of aqueous humor by dilating Schlemm's canal. This helps in safely and effectively lowering high intraocular pressure (IOP).
Aqueous humor is a clear liquid found in the anterior eye and is responsible for maintaining IOP. It is produced by ciliary processes and drains via the trabecular meshwork into the structure called the Schlemm's canal. When there is a blockage of the canal, causing build-up and inadequate drainage of aqueous humor, the patient experiences high IOP. In turn, elevated IOP causes glaucoma. Glaucoma can cause irreversible vision loss and is one of the leading causes of blindness in people over 60 years of age.
Canaloplasty uses a microcatheter/tube placed in Schlemm's canal (responsible for draining aqueous humor), thus widening/opening the canal. This helps improve drainage of the aqueous humor, relieving intraocular pressure. Canaloplasty can be performed alone or together with cataract surgery (PhacoCanaloplasty).
The following are the indications for canaloplasty:
- Primary open-angle glaucoma
- Pigmentary glaucoma - More common in young male myopes
- Children with congenital glaucoma
- Pseudoexfoliation glaucoma
It is safe for patients who:
- Are undergoing cataract surgery
- Are contact lens users
- Have gone through medical therapy
- Have had trabeculectomy surgery before, without a lot of scarring
- Have active lifestyles and need a short recovery time
- Are at a high risk of suffering hemorrhage or complications
Situations where canaloplasty shouldn't be done include:
- Narrow angles
- Angle recession
- Chronic angle-closure
- Neovascular glaucoma
- Patient has a surgery history that hinders Schlemm's canal cannulation
Since the procedure doesn't need operating on the anterior chamber, it is believed to be a safer option compared to traditional glaucoma surgeries such as trabeculectomy. Trabeculectomy is still considered the best glaucoma surgery, but it comes with several severe risks like infection, leakage, and irritation.
Other advantages of canaloplasty include:
- Long-term reduction of IOP
- Doesn't require a subconjunctival bleb
- Doesn't need the creation of a permanent fistula in the eye
- Lowers the use of glaucoma eye drops/medication
- Uses the eye's conventional drainage system
- Fewer postoperative complications
Some disadvantages include:
- A technical, steep surgical learning curve
- Technical surgical instruments
- Insufficient postoperative drop in IOP when compared to traditional glaucoma surgery
Before the Procedure
A few days to the surgery, the eye doctor will conduct a comprehensive eye exam. During the exam, s/he will check pupillary and visual field defects by conducting tests such as gonioscopy and slit lamp. The doctor will also perform routine blood tests, chest x-rays, and ECG to determine the heart and lung function.
The patient is advised to stop taking blood thinners and stop smoking (if applicable) for a few days before the surgery. Patients suffering from underlying conditions such as diabetes and high blood pressure will receive specific instructions on how to control their medication intake. Local anesthesia is administered during the surgery; therefore, the patient is requested to have a very light breakfast the morning of the operation.
The patient should also bring someone to take them home or arrange for transport, as their vision will be affected for a few days.
After arriving at the hospital, the patient will receive the appropriate wear and be requested to lie down on a specially designed table. The doctor will conduct an ultrasound to see Schlemm's canal for accuracy and precision. The eye specialist will then administer anesthetic in the form of eye drops or injection to the eyeball's tissue.
After the anesthesia begins to take effect, the eye specialist will make a conjunctival opening to expose the sclera. S/he then dissects and raises a triangular or parabolic scleral flap, about half the sclera's thickness. S/he then makes another incision that gives access to the Schlemm's canal, which is removed after decompressing the eye. After exposing the Schlemm's canal, a flexible microcatheter with a light at one end is inserted and pushed forward through the canal.
After the microcatheter has gone through the canal's entire 360 degrees, a suture is fixed to the other end of the microcatheter. This 'tying down' results in tension on the canal's inner walls, keeping the walls stretched open over a long period. As the suture is being tied, the microcatheter is slowly removed from the canal in the opposite direction, with the suture replacing it. A little amount of viscoelastic agent is introduced to the Schlemm's canal every two or three hours.
Once the suture comes out of the canal, it is knotted to distend the trabecular meshwork inwardly and keep the Schlemm's canal open. The suture now replaces the microcatheter. The superficial scleral flap is repositioned and closed tightly to close the sclera and conjunctiva. The eye is dressed and an eye shield is given to prevent injury.
The patient will be held for a few hours for monitoring of his/her vitals and discharged afterwards.
Risks & Complications
During surgery, one complication that can arise is IOP spikes. This may continue for a few days post-surgery but tends to go away. After the surgery, the patient will experience pain, inflammation, and sensitivity to light.
Although canaloplasty has significantly fewer risks than traditional glaucoma surgeries, it still has some potential risks and complications. These include:
- Hyphema - This is bleeding of the eye which normalizes on its own.
- Descemet’s membrane detachment - This occurs if the Schlemm's canal is too tight and the viscoelastic agent is introduced. Without treatment, this may lead to vision loss. To relieve this, the eye specialist injects a gas bubble into the eye that pushes the Descemet's membrane against the cornea.
- Suture extrusion
- Hypotony/Low IOP - This is a rare complication where the IOP drops to less than 5 mmHg, and it affects vision.
- 'Bleb' formation - Whereas this is a requirement during trabeculectomy, it is a complication for canaloplasty. However, it does not lower the effectiveness of the canaloplasty.
- Endophthalmitis - Infection of the eye
- Surgery failure - This is a rare complication seen in less than 1 out of 20 canaloplasty surgeries. When this happens, the patient may need traditional glaucoma surgery.
Aftercare & Recovery
The patient will be required to wear the eye patch for a few days to prevent injury to the eye. S/he will be given antibiotic eye drops to use for one week and topical corticosteroids for two to four weeks to help reduce the inflammation. Driving can be resumed after a week.
The patient should avoid getting any water into the eye, using eye make-up, and contact sports for a month. In case the patient has to engage in strenuous exercise or sports, s/he should wear protective eyewear that doesn't apply any pressure to the eyeball.
After a few weeks, the patient will be required to go back to the doctor's office for a review check-up. There are no dietary instructions that the patient will be required to follow after the surgery.
The procedure is considered successful when IOP is reduced by up to 40% and significantly lowers or eliminates the need to use glaucoma eye drops.