There has been a rapid proliferation in the number of surgical options for the treatment of glaucoma. Surgical options can be broadly divided into traditional incision surgery that includes trabeculectomy, deep sclerectomy and glaucoma drainage device surgery. The traditional surgeries share the characteristics of strong efficacy with a moderate risk of complications.
Modern surgeries are often referred to as MIGS (minimally invasive glaucoma surgery) these surgeries all share the common characteristic of being somewhat less effective than traditional surgery but are safer. MIGS can be characterised into procedures that augment the eye’s natural internal drainage pathways and those that create a small controlled flow to the external surface of the eye. The internal augmentation surgeries are generally undertaken in conjunction with cataract surgery.
Before I go any further, I need to make a very important point. Cataract surgery is probably the best glaucoma surgery. At the recent European Glaucoma Society conference in Florence the room was asked to vote on the best glaucoma surgery and cataract surgery was the hands down winner. If you have a cataract and someone is suggesting traditional surgery, you need to ask why not cataract surgery first?
What makes cataract surgery so good? It is very safe, improves your vision, gets you out of glasses. 98 or 99% of people end up with perfect vision and there is little in the way of post-operative discomfort. Cataract surgery in Australia can currently be combined with an iStent or a Hydrus to provide increased efficacy without noticeably increasing the risk or discomfort from the surgery.
Cataract surgery is the treatment of choice for angle closure glaucoma, which is one of the major sub-types of glaucoma. Patients with the other sub-type of glaucoma, open angle glaucoma, can also benefit from cataract surgery. The mechanism by which cataract surgery lowers the eye pressure is not completely understood but most studies suggest that on average patients’ pressure will drop by 5 after cataract surgery and an additional 2 or 3 if a stent or hydrus is also used. In many cases the pressure drop will be enough for patients to stop one eye-drop.
The iStent inject is the world’s smallest medical prosthesis at about 0.3 mm in size. It is approved for us in conjunction with cataract surgery. At the end of the cataract operation after the cataract has been removed and the artificial lens has been correctly positioned a special contact lens is used to allow the surgeon to visualise the internal drainage pathway, called the trabecular meshwork. The surgeon then injects the stent. through the trabecular meshwork, a structure that is about 0.3 mm wide. The stent should end in a natural drainage pathway called Schlem’s canal and facilitate the egress of fluid from the eye to Schlems canal and thus aid in the reduction of eye pressure.
The hydrus is a much larger device, at 12 mm, than the iStent. Similar to the iStent it is injected into Schlem’s canal with the surgeon utilising a special contact lens to visualise the trabecular meshwork. The canal is entered with a canula and the stent is slowly progressed into the canal with a small section remaining in the eye. The stent keeps the canal open and allows fluid to flow into the canal, again facilitating drainage of fluid and helping to reduce eye pressure.
Xen is considered a MIG but rather than enhancing the internal drainage pathway it creates a path from inside the eye to a bleb, or blister, of fluid under the conjunctiva, or clear skin over the white of the eye. Xan can be done in conjunction with cataract surgery but is more commonly performed as a stand-alone procedure.
It is probably not as effective as traditional drainage surgery but is probably much safer. The Xen is a small polymer tube that is inserted from the inside of the eye so that it lies just under the conjunctiva and sits under the upper lid. Fluid passes from inside the eye to the small bleb where it is absorbed by the body.
The Xen is most commonly used in patients who have previously had cataract surgery and who either don’t need as much pressure reduction as would be obtained with traditional surgery or in whom the risk of traditional surgery is considered too high.
Xen gel implant is used to create a pathway for fluid to travel from inside the eye to a small bleb under the conjunctiva.
Traditional surgery involves making a pathway for fluid to travel from the inside of the eye to the outside of the eye. The two main types of traditional or incisional surgery are trabeculectomy or tube surgery. The majority of traditional surgery is still trabeculectomy but there has been a trend towards more tube surgery as this may be a safer option that may provide better long-term success.
Trabeculectomy involves creating a flap in the sclera that allows fluid to pass out from the inside of the eye. The flap is carefully secured to allow a controlled amount of fluid to leave the eye, otherwise the pressure can drop too low. The fluid then pools within a bleb, or blister, under the conjunctiva and is absorbed by the body. Trabeculectomy is the best method to obtain very low pressures.
However, it often requires a lot of work in the post-operative period to adjust the rate of flow through the drainage flap. The bleb is prone to scarring and this will stop the fluid flowing into it and reduce the effectiveness of the procedure. In order to prevent scarring and medication is used at the time of surgery that prevent scarring.
Sometimes further injection must be injected next to the bleb after surgery if the bleb looks like it is scarring too much. If the flap is too loose and too much fluid leaves the eye, then the pressure can go too low and the vision becomes quite blurry. If the situation is not rectified, then permanent damage to the vision can occur.
Trabeculectomy is a delicate balance between allowing enough fluid but not too much to pass through the flap and into the bleb. This requires as much surgical skill after the procedure as it does during the surgery itself.
A flap is created in the sclera allowing fluid to egress from the eye. A bleb or blister of fluid is created overlying the scleral flap.
Tube surgery or glaucoma drainage device requires the insertion of a small tube into the eye. This can either sit just in front of the iris, or in patients who have had cataract surgery behind the iris. Fluid flows though the tube to a plate that is situated on the surface of the eye under the upper eyelid. The plate is covered by conjunctiva the clear skin overlying the white of the eye. The fluid forms a reservoir between the plate and the overlying skin and fluid is slowly absorbed from the reservoir. The size of the plate has been calculated so that the reservoir allows enough fluid to be drained to create a low pressure inside the eye.
Tube surgery was long thought to be riskier than trabeculectomy, however, with modern techniques it has actually been shown to be safer in several recent large studies. While tube surgery probably provides better long-term pressure control than trabeculectomy it is generally not able to achieve the very low pressures that some patients might need and may be better obtained with trabeculectomy.
Fluid exits the eye through a tube and is spread over a plate. The skin overlying the plate absorbs the fluid.
What should I expect after my surgery?
The post-operative course that you will expect after glaucoma surgery depends on the type of operation. If you have a hydrus or iStent inject performed at the time of cataract surgery you will have a similar post-operative course to a routine cataract. Most patients will expect to have not pain during surgery and only minimal discomfort after the operation. The eye may feel gritty for a few weeks to a few months and vision should be excellent on the morning after surgery, or within a week or two. Most surgeons advise patients to take it easy for the first week and refrain from strenuous exercise for a month after surgery.
The iStent and hydrus are placed within the eye and patient are unaware that they are there. They do not cause any sensation and cannot be seen except with the use of a microscope and special contact lens. Both products are safe for MRI scanning and will too small to raise concerns at airport security.
Patients who have a Xen gel implant should also experience no pain or discomfort during surgery. The eye may be a little irritated for a few days to a week after surgery and there can sometimes be some bleeding at the surgical site that will make the eye look red. The Xen Gel implants relies on the formation of a bleb, blister of fluid under the skin of the eye. Your surgeon will want to review you regularly to monitor the bleb and you may need to take a prolonged course of post-operative drops to help the bleb form correctly.
In as many as 50% of cases the surgeon may need to modify the bleb by using a small needle to enlarge it, this procedure is often done in the rooms but sometimes may require a trip back to the operating theatre.
Patient who have a trabeculectomy should experience no discomfort during surgery, but the eye is often quite uncomfortable for a few weeks to months after surgery. The post-operative course following trabeculectomy is notoriously turbulent during the first few months and it often takes 3 months to settle down. The eye can be painful if the pressure goes too high and can become blurry, often with a dull ache if the pressure is too low.
Many patients will need some sort of manipulation of the bleb to get it the right size so that the pressure in the eye reaches the appropriate target. Because the bleb is an external to the eye to will need long term monitoring by your surgeon and the life span of the operation is often 5- 10 years. Patients who have not had cataract surgery prior to having a trabeculectomy are likely to develop a cataract within a few years of the surgery.
Unfortunately, having cataract surgery after successful trabeculectomy is a common cause for the bleb to fail and the pressure in the eye to increase. This is one of the reasons that most surgeons will elect for a cataract-based operation if cataract surgery has not already been done.
Tube surgery is mainly done on patients who have already had cataract surgery but can be done on patients who have their natural lens in place, however, this is generally reserved for extreme cases of secondary glaucoma. Patients who have tube surgery should not experience any discomfort during surgery.
The post-operative course depends on if the conjunctiva is closed using glue or sutures. If sutures are used the eye can be quite painful for up to a month. If the surgeon uses glue to close the conjunctiva there is normally minimal pain. The tube is generally tied off with a suture so that the skin over the plate can heal. About 6 or 7 weeks after the surgery the suture is either removed, cut with a laser or dissolves allowing fluid to flow through the tube. The skin having healed over the plate will form a reservoir that should control the flow of fluid so that it does not go too low. There is much less post-operative work required in tube surgery than with trabeculectomy.
In summary, there are a growing number of surgical options to help lower your eye pressure and protect you from glaucoma. The decision as to which surgery is best for you will take into account a lot of factors and you should make sure you take the time to discuss what might be the best surgery for you with your surgeon.