When eye drops, pills, laser surgery, or other less invasive glaucoma surgeries (MIGS) fail to adequately control your eye pressure, your doctor may recommend a more aggressive filtration surgery called a glaucoma drainage implant or tube. It is often performed subsequently to a previously failed filtration surgery such as a trabeculectomy or Xen®. In addition, it might be the best option in particular types of glaucoma such as neovascular or uveitic, as well as eyes that have significant scarring from previous surgeries or injury. Tubes tend to be more resistant to scar formation than other filtration surgeries making them a good choice in these scenarios.
A glaucoma drainage implant or tube is a small prosthetic device that is implanted in the eye, bypassing the trabecular meshwork (traditional outflow drain), allowing fluid to drain from the eye resulting in a lower intraocular pressure. There are a few different drainage implant options and can be grouped into valved (Ahmed) and nonvalved implants (Baerveldt and ClearPath). The valved implants start working immediately when placed in the eye and the non-valved implants are generally tied off or obstructed with a suture, restricting flow initially and allowing the eye to heal prior to the tube opening. Once the suture dissolves or is removed/cut, the tube will begin to drain. Which implant is best for you is a complex decision and is based on multiple factors including the patient, type of glaucoma, and surgeon preference.
Regardless of the implant type, a silicone tube is inserted into the eye, generally in the anterior chamber (space between the iris and cornea). Other locations can also be used. The tube is connected to a plate and acts as a drain, allowing fluid to exit the eye. The plate is anchored to the eye underneath the conjunctiva. The fluid drains into a space between the plate and the conjunctiva and like a trabeculectomy can be referred to as a bleb. It is then reabsorbed into the body resulting in a lower eye pressure. The tube is usually underneath the eyelid and unless the lid is pulled back it should not be noticeable to the patient or their family. You may also notice a small clear or white patch when the eyelid is pulled back. This is a patch the surgeon places over the tube to limit irritation and limit the risk of long term tube exposure through the tissue.
A glaucoma drainage implant is done in an ambulatory surgery center under light intravenous sedation (like cataract surgery) and usually a local eye block. Following this procedure your eye is generally covered with a patch and removed the next day at your appointment. You will then be using post-operative medications and may be using some of your glaucoma drops depending on the implant type and your eye pressure at that visit. Following the initial appointment the day after your surgery, your surgeon will examine you closely for the first few weeks adjusting your eye drops as needed, particularly with the non-valved implants prior to them opening as discussed above.