Glaucoma refers to a group of conditions that result in damage to the optic nerve. The optic nerve is a bundle of nerve fibres that carries visual images or signals from the eyes to the brain. Loss of nerve fibres in the optic nerve leads to irreversibly reduced vision with a small percentage of those effected progressing to severe vision loss or blindness.
Types of glaucoma
The different types of glaucoma include:
- Open Angle Glaucoma: In this type of glaucoma, the angle between the iris and cornea is wide and open. As a result, the eye’s drainage system (trabecular meshwork) remains free of obstruction although increased resistance to fluid leaving the eye may still occur. This type of glaucoma may either be primary or secondary to other conditions such as pigment dispersion syndrome or pseudo exfoliation syndrome.
- Angle Closure Glaucoma: In this type of glaucoma, the angle between the iris and the cornea comes into contact resulting in a blocked trabecular meshwork. This may happen either quickly (acute) or slowly (chronic) and can be either primary or secondary to other conditions such as uveitis, neovascularisation or iridocorneal endothelial syndrome (ICE).
- Congenital Glaucoma: This type of glaucoma occurs before the age of 2 years and often runs in the family. It is caused by improper development of eye’s drainage channels before birth.
The goal of glaucoma treatment is to maintain a patient’s quality of life by limiting the effect glaucoma has on vision and vision-related tasks. The main strategy is for achieving this reduction of intraocular pressure as this has been shown to slow or halt glaucoma progression. This can be achieved by using special eye-drops or medications or by treating the eye with a laser. Surgery is recommended if medications and/or laser don’t yield the desired result, or with an aim to prevent further vision loss or blindness. Depending on your particular situation, options include:
Laser treatment is usually recommended if the use of eye drops does not control your glaucoma adequately. However, there is an increasing trend towards offering some laser treatments as first line therapy because of its good efficacy and safety profile.
Depending on the type of laser surgery, your eye will be numbed with anaesthetic eye drops. Then, your doctor will place a special lens in front of your eye. Afterwards, a laser beam is aimed into your eye and you can see flashes of coloured light.
Types of laser surgery for glaucoma include:
- Laser trabeculoplasty : Laser trabeculoplasty is often used to treat open-angle glaucoma. The laser is aimed at the trabecular meshwork, where fluid drains from the eye. This surgery opens the clogged areas and makes it easier for fluid to flow out of the eye.Selective laser trabeculoplasty (SLT) : During SLT, a non-thermal laser is applied to the trabecular meshwork in the angle between the iris and cornea.
- Laser iridotomy: Laser iridotomy is normally performed to treat people with closed or occludable iridocorneal angles. During iridiotomy, the laser creates a small hole through the iris to improve the flow of fluid from the back of the eye to the trabecular meshwork. This opening drains out the fluid and helps lower eye pressure.
- Cyclophotocoagulation or laser cyclo-ablation: Laser cyclo-ablation may be helpful in treating people with severe glaucoma, which has not been manageable with medications or surgeries. In cyclophotocoagulation a laser is used to destroy the parts of the ciliary body, a part of the eye that produces eye fluid. This therapy decreases the production of fluid thus reducing the eye pressure.
Risks and Complications
You may have a slight burning sensation in the eye during laser surgery. Your eyes may feel irritated and have slightly blurred vision. Rarely a short term increase or an excessive drop of intraocular pressure can also occur after laser surgery. Both of these complications can be managed with medications. You may also have a small risk of cataract formation after some types of laser surgeries for glaucoma.
Penetrating Filtration Surgery
- Trabeculectomy: Trabeculectomy is the most commonly performed surgical procedure to reduce intraocular pressure in the eyes with glaucoma. It involves the creation of a new drainage channel that allows the fluid to drain from the inside of the eye to a space under the conjunctiva leading to the formation of a fluid filled space termed the “bleb”. The drainage site may scar over time leading to its closure and subsequent elevation in eye pressure. This scar formation can be prevented or minimised by using antimetabolites during and after surgery. These act by inhibiting the multiplication of cells that form scar tissue.
- Express Shunt: This is a modified version of a trabeculectomy. This procedure uses an extremely small metal shunt to divert intraocular fluid in the same manner described for trabeculectomy. To date, evidence suggests outcomes are very similar to trabeculectomy
Non-Penetrating Filtration Surgery
A number of surgical techniques are classified under this heading including deep sclerectomy, viscocanalostomy and canaloplasty. The common feature of all these types of surgery is the lack of full-thickness incision in the inside of the eye. Instead, they aim to open and expose a structure called Schlemm’s canal, a circular passage that travels for 360 degrees around the front of the eye near the junction between the cornea (clear front part of the eye) and sclera (the white part of the eye). They lower intra-ocular pressure by increasing the flow of aqueous through the natural pathways of the eye as well as via a mechanism very similar to trabeculectomy (described above). These surgeries are only likely to work if the angle between the iris and cornea is open. Therefore, glaucoma in which this angle is closed should not be treated with this type of surgery.
- Deep Sclerectomy: This technique is similar to a trabeculectomy, except no full thickness drainage channel is created. Instead the dissection opens into Schlemm’s canal, but leaves the trabecular meshwork intact. Fluid from within the eye then flows across the trabecular meshwork and is then dispersed along Schlemm’s canal, under the sclera and into the “bleb”. The intraocular pressure reduction achieved is slightly less than a trabeculectomy, however, the speed of recovery after surgery is often quicker and it has a different complication profile. For example, cataract and chronically low intraocular pressure (hypotony) are less frequent following deep sclerectomy.
- Viscocanalostomy: a clear jelly-like material called viscoelastic is injected into Schlemms canal in an attempt to dilate it and increase the rate of fluid flow along it. This can be performed as stand alone procedure or in combination with other techniques such as deep sclerectomy.
- Canaloplasty: a fine suture is threaded along the entire circumference of the Schlemm’s canal and pulled taught. This opens the Schlemm’s canal and aids in the flow of fluid along it.
Minimally – Invasive Glaucoma Surgery
Known as MIGS, minimally-invasive glaucoma surgery is a new and evolving area of glaucoma surgical treatment. It aims to lower intraocular pressure with a procedure or device that is minimally invasive and has little or no effect on the surface layers of the eye. All MIGS procedures have the following characteristics:
1) performed within the eye in the junction between iris and cornea (iridocorneal angle).
2) minimal tissue handling or destruction.
3) relatively quick.
4) very good safety profile.
5) multiple treatments are possible.
6) can be combined with cataract surgery.
MIGS is best suited for eyes with mild to moderate glaucoma or ocular hypertension with an open angle in whom an intraocular pressure in the mid to high teens is desirable. MIGS can also be helpful in reducing the need for topical glaucoma medication.
Two MIGS devices are currently approved for use in Australia:
- Hydrus: this device is approximately the size of an eyelash and is made of a metallic alloy called Nitinol. Via a small incision in the cornea it is inserted into Schlemm’s canal in the iridocorneal angle. There is an opening at one end through with fluid from the anterior chamber of the eye can flow into Schlemm’s canal then leave the eye via the natural outflow pathways.
- iStent: this device measures 1.0mm x 0.3mm, is made of titanium coated in heparin and has a similar shape to a snorkel. It is positioned via a small incision in the cornea into Schlemm’s canal in the iridocorneal angle. The opening at the end that lies within the anterior chamber allows fluid to flow directly into Schlemm’s canal and then leave the eye via the natural outflow pathways.