This document is intended to help patients understand more about Ahmed tube implantation for glaucoma. If you have any questions, please ask your surgeon.
One purpose of glaucoma surgery is to lower the eye pressure to protect the vision from further glaucoma damage. This is specifically important in patients with uncontrolled pressures despite maximal medical therapy who are at risk for further vision loss.
The additional benefit of glaucoma surgery is to reduce one’s dependence on eye drops. After implantation, the tube shunt is very effective in lowering the eye pressure; this allows the eye pressure to be controlled with much fewer eye drops (in some cases, no eye drops at all). This is specifically helpful in patients with significant eye drop intolerances/allergies or those who have difficulty keeping up with instilling eye drops on a daily basis. By reducing one’s need to use eye drops on a daily basis, glaucoma surgery can help improve one’s quality of life.
Most glaucoma tube shunts consist of a flexible tube connected to an external reservoir (similar to the shape of a computer mouse). The reservoir is fixated to the outside surface of the eye; the tube enters the eye to drain the intraocular fluid. The fluid collects in the reservoir and then is distributed to the outside of the eye, where it is absorbed by the eye’s own veins and transported out of the eye cavity. The tube shunt and the flow of fluid are underneath the eye’s external covering (called the conjunctiva), so it is typically not visible or noticeable to the naked eye.
Diagram of placement of glaucoma tube shunt implantation (Courtesy of www.aao.org)
There are several glaucoma tube shunt implants available on the market. These implants are typically made of synthetic polymers (often silicone or polypropylene). Each device type has their own advantages and disadvantages. The implant device used is selected based on the patient needs, the specific eye condition, and surgeon preference.
The Ahmed glaucoma tube implant is a ‘valved’ implant, with a mechanism to limit the flow of intraocular fluid exiting the eye. This helps prevent the eye pressure from dropping too low (a condition called hypotony). Often, patients may need to use supplement eye drops (eg, a single eye drop twice a day) after implantation surgery to help keep the eye pressure at a goal level.
The Ahmed glaucoma valve, made by New World Medical (https://www.newworldmedical.com/ahmed-glaucoma-valve/)
The eye tends to create scar tissue over these implants, which can block the flow of fluid. This can reduce the implant’s functionality or even cause it to fail completely; this can occur quickly after surgery, or slowly over a long period of time. Sometimes, tube shunt implantation surgeries are supplemented with off-label use of antifibrotic medications – medications to prevent scar tissue formation – to help keep the implant working well for a longer period of time. A common medication used for this purpose is called ‘mitomycin C’; it is used in a micro-dose amount to limit scar tissue formation over the implant.
The surgery will take place in an operating room; it is outpatient surgery, meaning you can return home after the surgery is done. You will be asked to not eat and drink anything several hours prior to the surgery. Due to the risk of bleeding complications after device implantation, you may be asked to stop taking blood thinners prior to surgery (if it is safe for you to do so – this is based on a discussion between your surgeon and medical doctor). You should continue any eye medications prior to the surgery unless specifically told to you by your surgeon.
The surgery is typically done under monitored anesthesia care, which involves local or regional anesthesia around the eye and light sedation through an IV. All forms of anesthesia carry risks, with complications including respiratory and cardiac problems and in rare cases, death. Your anesthesiologist can discuss with you the benefits and risks of anesthesia.
The surgery itself typically takes 60 to 90 minutes depending on the complexity. After the surgery is done, the eye is patched shut, and you can return home after you recover from the sedation. The eye remains patched shut for the remainder of the day until the next day; no eye drops are needed after the surgery in the operative eye (including your glaucoma medications).
Patients are typically seen several times in the post-operative period, including day 1, week 1, and month 1. Some patients may be asked to come in more frequently if there are issues in the post-operative course. During this time, patients will use several eye drops to help the eye heal and to prevent infection; these drops may include some, all or none of your usual glaucoma medications (depending on your course).
Every patient heals at different rates. but most require 2-3 weeks for vision to stabilize and 6-8 weeks for irritation and redness to improve. This depends on how the eye is healing and if any issues occur during the post-operative course.
These complications occur very rarely and are typically addressable with medications, or in rare instances additional surgeries. Your surgeon and eye doctor will continue to monitor your eye health after surgery to ensure your eye remains safe and stable after surgery.
Glaucoma tube shunt implantation (eg, Ahmed tube implantation) is an effective surgery to help control glaucoma, reduce dependence on eye drops, and overall help stabilize and improve quality of life. Please speak with your glaucoma specialist/surgeon if you have any further questions regarding this option.
