Glaucoma is not all the same
Glaucoma is an umbrella term, which describes diseases that affect the optic nerve at the back of the eye. The optic nerve is the pathway of vision from the eye to the brain, and is not repairable once damaged. Protecting the nerve from injury is important.
There are other diseases that affect the optic nerve, which are not glaucoma, and so the common thread in glaucoma is intraocular pressure, or eye pressure, which is elevated. The problem is that people’s sensitivity to eye pressure varies so one person’s elevated pressure might not be a problem for another.
Intraocular pressure can rise above normal for that eye for all sorts of reasons, and may do so only intermittently. In general we describe glaucoma in terms of open angle, or closed angle.
Open Angle Glaucoma
Open angle means that there is nothing in front of the drain plug, the angle, which we can see. It may mean that things have deposited into the drain plug and obstructed it, or that it has become inflamed, or that is has become non-porous over
Angle Closure Glaucoma
Closed angle means that the iris has obstructed in front of the drain plug.
In general we try to prevent the angle closure from developing, but we wait until we are clear that open angle glaucoma is occurring.
There are many other types of glaucomas, including inflammatory, trauma, lens induced, pigmentary, in relation to other eye surgery, steroid induced and more.
Glaucoma is all about prevention of change. Some people have an eye examination, which has features that could be glaucoma. It may not be possible to say ‘yes’ or ‘no’ at one visit, and often it is better to consider glaucoma in terms of risk management.
The principle risk is that of loss of vision so the aim is to understand a rate of change. Detecting rates of change requires objective measurements. All measurements have a degree of “noise” in them and the more accurate they are, the better they will tell change.
Lasers for glaucoma
Lasers have a large role to play in ophthalmology as the clarity of the front of the eye allows laser light to enter the eye. There are many different types of laser, both in ophthalmology and in glaucoma, so one person’s experience of laser may well be quite different from another, as in may in fact be different laser.
The common types of laser are:
Laser Peripheral Iridotomy
• Peripheral iridotomy is performed for angle closure mechanism, or where the iris maybe occluding, or there is a risk of occlusion of, the angle. This is angle closure, and laser iridotomy is remarkably successful at reducing the risk. Laser iridotomy does not change the focus or appearance of the eye and is invisible to the patient. It does, however, markedly reduce the risk in patients who have risk of angle closure.
• Laser trabeculoplasty has been a therapeutic modality since 1982, but in the early 2000s the laser changed to a non-heating laser, which is able to be repeated and is as effective as, or more effective than, the original argon laser trabeculoplasty. SLT, or selective laser trabeculoplasty, can be done in the rooms, causes minimal discomfort, and can be very effective in lowering intraocular pressure without drops. a recent NH&MRC study, partly performed through Melbourne Eye Specialists, is aimed at identifying whether or not SLT is better as first line instead of our current paradigm where we would tend to use drops as first line.
Other lasers include:
• Cyclodiode laser, which is done in a hospital. This reduces the amount of fluid production in the eye and can decrease the intraocular pressure that way; and
• Iridoplasty, which can change the form of the iris, particularly if the iris is becoming entrapped in the angle in spite of peripheral iridotomy.
Laser is sometimes used postoperatively, either for suture lysis or for goniopuncture after non-penetrating glaucoma surgery.
Trabeculectomy remains the mainstay of glaucoma surgery. Trabeculectomy was so named for the removal of the trabecular meshwork, but in fact the major way trabeculectomy works is by filtration of fluid from the inside of the eye into the tissue around the eye. This is all performed underneath the upper lid, and this procedure has evolved markedly over the last 40 years.
It is done in a hospital, under local anesthetic usually, and usually as a day case. It involves making a small hole in the wall of the eye, which is covered then by a partial thickness flap. Resistance to fluid flow is achieved by releasable stitches, the area is soaked in an anti-inflammatory material and then the tissue closed in a watertight fashion. Trabeculectomy has different variations and some of these are valuable at improving outcome or decreasing complications in particular types of eyes.
Trabeculectomy is an imperfect operation, but it is dramatically better than it used to be and it is employed when it is unsafe to allow the eye to continue with medical treatment only for the glaucoma.
It is rare for the glaucoma operation to fail early, but it can, and then may well need further intervention by the surgeon.
One of the big advances in glaucoma surgery over the last 20 years has been the increasing success of fixing the problems that arise in glaucoma surgery. In general these will be where the glaucoma operation fails to lower the pressure satisfactorily, where the pressure is too low, or where the operation produced an unintended side effect.
All of these issues are resolved by revision of the trabeculectomy, which involves a number of different types of operations, which are performed less commonly but now with much greater success.
Revision trabeculectomy is a subspecialty area and can be very successful in quickly resolving problems that develop.
A/Prof Michael Coote has written and talked extensively on revision trabeculectomy and is considered a world expert in this area. Revision trabeculectomy may not be the appropriate solution where a previous operation has failed, but its role and success has expanded markedly and it has offered, for a great number of patients, a simple and effective solution to their problems
Non-penetrating Glaucoma surgery
Non-penetrating glaucoma surgery is a newer advance in the history of glaucoma filtration surgery. As the name suggests, it differs from standard trabeculectomy by not completely entering the eye. The intent is to make the eye wall more porous and lower the pressure at a more regulated, gentle way, reduce the postoperative complications as well as the number of postoperative visits.
Non-penetrating glaucoma surgery has come a long way since its first iterations and has now a significant role to play. It is not for everyone and is not likely to completely supplant trabeculectomy. It does, however, have a role to play; it may be better for some patients facing glaucoma surgery. Please ask one of our doctors if you are appropriate for non-penetrating glaucoma surgery.
Deep sclerectomy is a version of non-penetrating glaucoma surgery. In this, the sclera is excised underneath the flap in order to make a porous chamber and allow fluid to exit the eye in a more controlled way. It does offer some advantages as well as some disadvantages and, as usual, the question of whether it is appropriate for you will be answered in consultation with your doctor. Non-penetrating glaucoma surgery and deep sclerostomy are two procedures that are only offered through Melbourne Eye Specialists.
Canaloplasty is an elegant technique, which involves opening of Schlemm’s canal. Schlemm’s canal is the main collecting duct for aqueous; dilating this and allowing higher levels of flow out of the eye without opening directly into the front of the eye offers advantages. Canaloplasty is evolving and it may have a role in certain types of glaucoma.
Melbourne Eye Specialists offers canaloplasty to its patients, but the decision about whether or not it is right for you, needs to made in consultation with a treating ophthalmologist.
Viscocanalostomy is an opening of Schlemm’s canal using a viscous substance, usually Helon, often used ta the time of cataract surgery. Viscous material is injected into Schlemm’s canal to dilate it, but nothing is left in place and is usually combined with deep sclerectomy or non-penetrating glaucoma surgery.
Its role in the treatment of your glaucoma needs to be discussed with your treating ophthalmologist. Melbourne Eye Specialists offers viscocanalostomy in context of deep sclerectomy and non-penetrating glaucoma surgery.
Glaucoma Drainage Devices (GDDs)
Glaucoma drainage devices is an umbrella term used to describe two main tube and plate devices, which have been available to patients for many years. These two are the Molteno implant and the Baerveldt implant. Both implants are structurally quite similar and involve the insertion of a very fine tube into the front part of the eye, allowing fluid, aqueous, to drain to a plate, which is placed around the outside of the eye but underneath the tissue, up underneath the upper lid.
The use of glaucoma drainage devices has, in the past, been restricted to more complicated situations, but the role of these devices is getting revisited and refined as new research emerges.
Melbourne Eye Specialists offers both a Molteno and Baerveldt implant for patients, but, as usual, the choice will be in consultation with your ophthalmologist.
Prof Tony Molteno, who designed the Molteno implant, did so whilst living and working in South Africa. Many years ago he emigrated to the south island of New Zealand where these implants are still made. The Molteno implant has gone through a number of revisions and the Molteno 3 implant, the one we now use, is a refined and highly tested device, which is used in a variety of circumstances, often where other forms of glaucoma surgery are less likely to be effective.
George Baerveldt designed this implant in the early 1980s and many of these implants have been used around the world. It is not structurally dissimilar to a Molteno implant and indeed both Baerveldt and Molteno both originate from South Africa where glaucoma in the black community has traditionally been very difficult to manage and no doubt stimulated this work. The Baerveldt implant is implanted in a very similar way to the Molteno implant and the choice between the two, the Molteno and the Baerveldt, is often not a critical one.
Melbourne Eye Specialists offers both Molteno and Baerveldt implants for their patients, and the choice and process will be discussed with your ophthalmologist.
Cyclodiode laser is a method of reducing aqueous production in the eye. It is a laser that is done under a local anaesthetic and relatively high-powered laser is passed across the wall of the eye in order to reduce the production of aqueous. Cyclodiode laser is usually performed where other treatment options have also been employed. It is most often used as an adjunct, but can be used as a primary treatment in uncommon circumstances. Cyclodiode laser is only offered through the Royal Victorian Eye and Ear Hospital, but all three of our glaucoma doctors have appointments at the Eye an Ear Hospital and can perform cyclodiode laser on Melbourne Eye Specialists patients in that facility.
Glaucoma is still the second most common cause of blindness in the world, and the most common avoidable one. Glaucoma can be a complicated disease to treat, but there is never a time when there is nothing more that can be done. But glaucoma treatment is about avoiding losing vision - so it must not be left too long.
Minimally Invasive Glaucoma Surgery (MIGS)
MIGS is a recent term which covers a variety of new devices: the classic MIGS devices are "trans-trabecular" - in other words the traverse the trabecular meshwork and seek to reinstate aqueous flow into the original canal (of Schlemm). The two available in Australia are the iStent and the Hydrus and they operate in a similar manner. There are reasons to be optimistic about them but in general they are used for less threatening glaucoma.
The CYPASS implant is newer and is placed inside the layers in the eye. It drains aqueous into the back of the eye. There are specific indications for this implant and for those it is a good alternative.
The XEN implant is more akin to standard filtration operations (such as the trabeculectomy and non-penetrating glaucoma surgery). The implant improves the reliability and speeds the recovery from the procedure and is becoming an attractive alternative to the larger glaucoma operations. (Assoc Prof Coote chairs the advisory committee for XEN through Allergan).