Canaloplasty

Canaloplasty is a minimally invasive surgical technique used to lower intraocular pressure, or pressure inside the eye, in individuals affected with glaucoma. The technique utilizes a microcatheter to perform a 360-degree cannulation of Schlemm’s canal to enlarge the drainage canal and alleviate pressure inside the eye.

Canaloplasty involves circumferential dilation and stenting of Schlemm's canal with a viscoelastic agent and a Prolene suture. Schlemm's canal is the drainage channel into which intraocular fluid drains after passing through the pores of the trabecular meshwork. It is a circular microscopic canal that lies within the eye tissues at the junction of the cornea and the sclera. Canaloplasty lowers intraocular pressure by restoring the trabeculocanalicular outflow pathway. It increases the flow of aqueous humor from the anterior chamber, through the trabecular meshwork and Descemet's window, into and around Schlemm's canal, and out through the collector channels.

Indications

Canaloplasty is indicated for the treatment of open-angle glaucoma - the most common form of glaucoma.

Glaucoma is an eye disease that adversely affects the optic nerve – the nerve that supplies visual information from your eyes to your brain. With glaucoma, damage to the optic nerve can occur due to an abnormally high intraocular pressure. This pressure is due to too much aqueous humor, the clear liquid inside the front part of the eye that helps nourish the eye. When this fluid does not properly drain from your eye, it builds up and exerts pressure on the optic nerve, which can lead to nerve damage and vision problems.

Aqueous humor usually drains through tissue located at the angle where the iris and cornea meet. This tissue, known as the trabecular meshwork, is a network of small canals that aid in draining the aqueous humor from the eye. Open-angle glaucoma occurs when the drainage angle formed by the cornea and iris remains open, but other areas of the drainage system do not drain properly, leading to a slow, gradual increase in eye pressure. Open-angle glaucoma typically affects people over 50, often in both eyes, but usually more pronounced in one.

Contraindications

Canaloplasty is contraindicated in individuals with angle recession, angle-closure glaucoma, neovascular glaucoma, narrow angle glaucoma, narrow inlets with plateau iris, and in individuals with previous surgery which would prevent 360-degree catheterization of Schlemm's canal.

Preparation

In general, preparation for canaloplasty surgery will involve the following:

• A review of your medical history
• An eye exam to check the pressure of your eye, look for an open angle, measure the thickness of your cornea, and assess the overall health of your eye
• Providing your physician with a list of medications and supplements you are taking
• Adjusting the dose of medications you are on, or stopping certain medications, such as blood thinners or supplements such as Vitamin E and/or Fish Oil? Omega 3 for at least a week prior to surgery
• Informing your doctor of any recent illnesses or other medical conditions you have, such as heart or kidney disease
• Refraining from eating or drinking at least 6 hours before the procedure. If you are on regular medication for conditions, such as high blood pressure, diabetes, or heart disease, you may take it with a sip of water.
• Avoiding wearing any eye make-up
• Arranging for someone to take you home after the procedure
• Signing an informed consent form

Surgical procedure

Canaloplasty surgery is usually performed in the operating room under local anesthesia with intravenous sedation. In general, the procedure will involve the following steps:

• The surgery eye is cleaned and numbed with anesthetic eye drops.
• An eyelid holder is placed over the eye to prevent the eye from blinking.
• Your surgeon creates a half-thickness triangular or parabolic scleral flap, followed by a deep scleral flap that exposes and unroofs Schlemm’s canal and creates a Descemet’s window. The deep flap is excised and removed.
•  A catheter with a fiber optic light and lumen (for injection of the viscoelastic) on its end is then inserted into Schlemm’s canal.
• The catheter is gently passed around the circle until the tip emerges on the other side. Passing the probe through Schlemm’s canal helps to break the septa inside the canal, and the viscodilation expands the canal.
• A suture is then tied to the catheter. As the catheter’s direction is reversed and it is withdrawn from the canal, the suture replaces it. The suture is then tied tightly enough to stent the canal open.
• Finally, the superficial scleral flap and conjunctiva are closed so as to be watertight.

Postoperative Care

Your surgeon will provide a series of postoperative instructions to be followed for a defined period. These include:

• The use of steroid and antibiotic eye drops to minimize the risk of infection and inflammation
• Wearing an eye shield to protect the eye and prevent rubbing it in your sleep
• Taking time off work for a few days to rest the eye and promote healing
• Avoiding sports activities or exercises that may stress the eye
• Avoiding getting soap in your eye
• Avoiding hot tubs or swimming
• Avoiding cream, lotions, or make-up around the eye
• Refraining from driving until your vision is restored
• Wearing sunglasses to protect the eye outdoors

Risks and Complications

The risks and complications of canaloplasty may include:

• Bleeding
• Infection
• Discomfort
• Bleb formation (a blister-like bulging of fluid)
• Suture extrusion
• Insufficient drop in pressure
• Hyphema – a collection or pooling of blood at the front of the eye

Summary

Canaloplasty is an innovative, highly effective, and non-perforating surgical technique that takes advantage of the conventional drainage system of the eye to safely treat elevated pressure in patients with glaucoma. It aims to restore the physiological outflow pathways of the aqueous humor and is independent of external wound healing. Several studies have demonstrated that canaloplasty is effective in reducing intraocular pressure and has a low rate of complications and several advantages, especially when compared with trabeculectomy, the gold standard for glaucoma surgery.