Glaucoma Laser, Filtering Surgery and Aqueous Shunt Devices
Glaucoma is condition characterized by progressive optic nerve damage and is very often due an increase in intraocular pressure (IOP). It cannot be cured but early detection and treatment can help to prevent vision loss and blindness, primarily by reducing the intraocular pressure (IOP). Medication in the form of eye drops or oral drugs are the first line of treatment. If these cannot be used or fail to give the desired results, the various surgical methods may be considered.
Laser treatment can be considered for both types of glaucoma – open angle glaucoma and angle-closure glaucoma. If glaucoma affects both eyes, then laser surgery is usually done one eye at a time, with an interval of a few weeks between the sessions. The type of laser surgery will depend upon the form and severity of the glaucoma.
Laser trabeculoplasty helps to open the fluid outflow channels so that fluid can drain easily out of the eye and decrease the IOP. A high-intensity beam of light is used to treat the drainage angle of the eye. Laser trabeculoplasty is usually done as an outpatient procedure for patients suffering from open angle glaucoma. This procedure is not suitable for treating angle-closure glaucoma.
There are 2 types of laser trabeculoplasty :
- Argon laser trabeculoplasty (ALT) – a high-intensity beam of light (laser) is used to open the drainage angle of the eye.
- Selective laser trabeculoplasty (SLT) – a lower level laser is used to open the drainage angle of the eye.
Laser trabeculoplasty is a painless procedure but a sensation of heat may be felt in the eye during the surgery. Anesthetic drops are applied to the eye before starting the procedure. During laser therapy, the patient sits facing the laser machine, with the doctor holding a special lens (goniolens) to the eye. A special microscope (slit-lamp) and goniolens help to guide the laser beams to the canals (trabecular meshwork) where fluid drains from the eye. A few small burns are made on the trabecular meshwork by the laser beam, which stretch the drainage holes, thus effecting easier outflow of fluid from the eye. Eye drops are instilled in the patient’s eye before or after the procedure to decrease the fluid in the eye and prevent an increase in IOP immediately after laser therapy.
Long Term Effects and Complications
The effect of laser surgery may wear off over time and conventional surgery may need to be done later. Even after undergoing laser surgery, the patient may need to continue taking medication for glaucoma. Some of the complications that may arise with laser surgery include :
- Eye inflammation
- Increased IOP
- Cloudiness of the cornea
- Excessive scar tissue formation
- Decreased vision, which may be temporary
- Permanent loss of vision
Laser Peripheral Iridotomy
This is conducted for angle-closure glaucoma and involves opening a new channel in the iris. It may be done as an emergency procedure to relieve pressure within the eye, or as a means of preventing an acute attack. A small hole is created in the iris, which makes it fall back from the fluid channel, thus helping the fluid drain.
Laser cyclo-photocoagulation or cyclo-ablation uses different types of lasers to destroy and thus hamper the ciliary body’s ability to make fluid thereby reducing the intraocular pressure (IOP). The procedure may need to be repeated in some cases to permanently control glaucoma. It is more often used in end-stage glaucoma or where all other methods fail, since there is a risk of vision loss with this technique.
Conventional Surgery or Filtering Surgery (Trabeculectomy)
In conventional surgery, which is usually done when medication and laser treatment have failed to give the desired results, a new opening is made for the fluid to drain out of the eye. Conventional surgery is also known as filtering microsurgery or cutting surgery. Trabeculectomy is the most common type of glaucoma surgery.
The surgery is painless since it is usually done under local anesthesia with intravenous sedation. It is usually done as an outpatient procedure and does not need overnight hospital stay.
In filtering microsurgery, a tiny drainage hole is made in the sclera (sclerostomy), which allows fluid to leave the eye, thus reducing IOP. A flap is created so that fluid can leave the eye without deflating the eyeball. A tiny piece of the iris may be removed (iridectomy), to allow the fluid to flow backward into the eye. A small bubble, known as a bleb, may form over the opening. This is a sign that fluid is draining out. Although the perfect surgery should not have a bleb, a thick bleb is preferred over a thin bleb since there is less risk of leakage in the former type.
The complications and risks of filtration surgery may include :
- Bleb leaks and infection.
- Scarring around the incision may close the drainage channels.
- Increased risk of cataract formation.
Aqueous Shunt Devices
Drainage implants (tube shunts) may be used to drain fluid in special cases like when :
- the glaucoma does not show good response to standard procedures.
- glaucoma is caused by swelling of the iris.
- glaucoma is caused by abnormal vessel formation.
- there is iridocorneal endothelial (ICE) syndrome.
The procedure involves inserting an implant, usually a ½ inch silicone tube, into the anterior chamber of the eye. The fluid is drained through the implant onto a tiny plate under the conjunctiva. The collected fluid gets absorbed by the tissues in the eye.
The complications may include :
- Very low IOP or hypotony
- Detached retina (retinal detachment)
- Corneal breakdown
- Strabismus (squint)
- Diplopia (double vision)
Non-Penetrating Surgical Techniques
Viscocanalostomy and deep sclerectomy are less invasive procedures than filtering surgery. In these techniques, the anterior chamber of the eye is left intact and bleb formation is avoided. A flap is created in the outer part of the sclera, while a thick piece of sclera is removed beneath it. These procedures are less effective than conventional surgery in lowering IOP.