YAG laser peripheral iridotomy

Glaucoma can be divided into the open and closed angle forms. The angle is the part of the eye through which fluid drains away. If it is ‘narrow’ then the pressure in the eye can rise and cause damage to the optic nerve and then to the vision. Angles can be examined clinically by looking directly at them using a gonioscope and/or by OCT scan. If deemed to be narrow then it may be necessary to open the angle to prevent or treat a rise in eye pressure. A sustained rise in pressure can cause a permanent loss of peripheral (side) and central vision and to treat a narrow angles, there are two ways to open the angles.

First, the YAG laser peripheral iridotomy (YAG PI) is something that has been performed for many years and bypasses the normal pathway of fluid flow around the eye by creating an ‘overflow valve.’ This helps the fluid to circulate freely within the eye minimising the risk of a sight-threatening pressure rise.

Second, lens extraction/cataract surgery can also have the same effect and has been advocated in an important study published recently in the Lancet. This is usually reserved for patients over 55 years with a high ocular pressure (over 30mmHg).

The advantage of the iridotomy is that it can be done easily in the outpatient clinic on both eyes at the same time and as it does not involve cutting into the eye, there is no risk of infection getting inside the eye. The laser uses the transparent properties of the ocular surfaces to penetrate the eye and make a small hole or ‘iridotomy’ in the iris. Fluid can drain from the back of the eye through to the front and through the drainage angle unimpeded by obstruction between the iris and lens. The procedure is performed sitting-up at a machine similar to that used when the eye is examined in the eye clinic, with your forehead resting at a headpiece and chin on the chin rest. Eye drops are used as anaesthetic to numb the surface of the eye and a contact lens will be placed on the eye. This prevents you from blinking and is used to focus the laser light. You will see some bright flashes of light and hear some clicking noises. The procedure usually takes a few minutes.

Risks of YAG laser iridotomy include:

• Rise in eye pressure
• Inflammation
• Bleeding in the front of the eye
• Clouding of the cornea
• Cataract
• Ghosting/doubling of image

The eye may be a little pink and a little sore and vision may be disturbed for the remainder of the day. You will be supplied with eye drops to help settle the inflammation.

Lens extraction by contrast is an operation, effectively the same as cataract surgery. By removing the natural lens and implanting a thin silicone lens, it creates more space for fluid to get from the back to the front part of the eye without obstruction. It is effective and in selected cases may offer more long-lasting benefits to the narrow angle patient, particularly with raised ocular pressure. If there is a cataract present then this operation will also treat this and improve the vision. If not, as patients with narrow angles are often long-sighted or ‘hypermetropic,’ this surgery will also potentially reduce the need for wearing glasses or contact lenses.

Both YAG laser peripheral iridotomy and lens extraction will:

• Prevent an attack of acute glaucoma
• Treat an attack of acute glaucoma
• Treat chromic glaucoma where the drainage channel is very narrow

Neither procedure usually needs to be repeated but ongoing follow up may be required even after these procedures.