• Reference Number: HEY1544/2025
• Departments: Ophthalmology Department
• Last Updated: 31 August 2024

Introduction

This leaflet has been produced to give you general information. Most of your questions should be answered by this leaflet. It is not intended to replace the discussion between you and the healthcare team but may act as a starting point for discussion. If after reading it you have any concerns or require further explanation, please discuss this with a member of the healthcare team.

Intraocular Pressure

For our eye to function normally, it must maintain a certain eye pressure. Eye pressure: also called intra-ocular pressure, is a measurement of the fluid pressure inside the eye. A normal eye pressure is necessary to inflate the eye and maintain the correct shape and optical properties of the eyeball.

A person with an elevated eye pressure is at risk of developing an eye condition called glaucoma. Glaucoma is a progressive multifactorial eye disease characterised by damage to the optic nerve (the part of the eye that connects the eye to the brain) and cause progressive visual loss. If left untreated, glaucoma can lead to irreversible blindness. Raised intraocular pressure without optic nerve damage is termed ocular hypertension, which, in some patients if not lowered, can progress to the development of glaucoma.

There are many risk factors for developing glaucoma. However, the only known modifiable risk factor is eye pressure. Consequently, lowering eye pressure reduces this risk of developing glaucoma or the possible worsening of a patient’s current glaucomatous eye disease.

Increased eye pressure is commonly treated successfully with topical ocular medication (eye drops); which can lower the pressure inside the eye to a satisfactory level. If the use of ocular medication fails to achieve the desired reduction in eye pressure or their use is not a practical option, alternative treatments may be indicated, such as laser. Selective laser trabeculoplasty (SLT) is a safe method to aid lowering eye pressure and can be used in conjunction with eye drops or alternatively, as a first-line treatment.

The Anatomy

For the eye to retain a normal eye pressure, a clear, watery fluid called aqueous humour is produced. Both the formation and reabsorption of aqueous humour are physiologically important processes for maintaining normal eye pressure and ocular function. Aqueous humour is produced by a structure in the eye called the ciliary body (situated in the back part of the eye); it flows into the front part of the eye and out of this space through a spongy tissue called the trabecular meshwork and into a drainage canal.

The inner pressure of the eye depends on the balance between how much fluid is made and how much fluid drains out of the eye. If your eye’s drainage system is working properly, then fluid can drain freely out to prevent pressure build-up but impairment in fluid outflow results in the elevation of the eye pressure. In certain patient the drainage area (trabecular meshwork) can become ‘clogged up’ over time, resulting in increased resistance which gradually increases eye pressure.

What is SLT?

SLT is a form of laser treatment that is used to reduce eye pressure. The laser treatment targets the drainage area of the eye, known as the trabecular meshwork. The laser modulates the trabecular meshwork, improving the outflow of fluid and as a result, reducing the resistance.

Who is a good candidate for SLT?

Patients suitable for SLT are those who have a diagnosis of either:

• Primary open-angle glaucoma
• Secondary open-angle glaucoma
• Ocular hypertension

In all these ocular conditions, the drainage system in the front part of the eye is open. Patients with closed angle glaucoma or narrow anterior chamber structures are unable to undergo SLT, as the procedure can increase their eye pressure.

How does SLT work?

Laser energy is applied to the drainage tissue in front of the eye (the trabecular meshwork). This causes both a chemical and biological change to occur, which results in better drainage of fluid through the trabecular meshwork and out of the eye. This eventually results in lowering of eye pressure. However, it may take up to 3 months for the full treatment effect to occur.

SLT is performed to protect a patient’s sight, and it will not restore any sight you may have already lost or improve your sight. It is successful in about three out of four patients (about 75% of patient). The effect will generally last between 1-5 years or in some cases longer. SLT may be repeated multiple times so long as there is an initial pressure-lowering response to the first treatment.

If SLT fails to lower the eye pressure, other treatments such as medications or surgery may be required. Having SLT does not affect the success of these other types of treatment.

What happens on the day of the SLT procedure?

You will attend the outpatient department (for approx. 2 hours) on the day of the laser procedure and this will be carried out in the laser treatment room. Initially, your vision will be checked, so please remember to bring your glasses with you.

Eye pressure might be measured before the laser procedure. Anaesthetic drops together with a drop to prevent a post-laser pressure rise will be instilled. It is important that you use your regular eye medication as normal on the day of your laser treatment.

Usually, an eye drop to make the pupil smaller is also instilled – this can sometimes give you an ache around the eye or a headache, which starts to wear off in an hour or two.

You will then sit at a machine similar to the one used to examine your eyes at the eye clinic, but with a special laser attached to it. A lens will be put on your eye before applying the laser beam. This lens allows a clear view and helps apply the laser to the drainage channels. During the laser treatment, you might see some flashes of light and hear clicking noises, but these are normal. Most patients tolerate the laser treatment well, but some might feel slight discomfort probably due to the lens but no pain as the anaesthetic drops are used to numb your eye which have been given beforehand. The laser procedure takes about 10 to 15 minutes per eye to complete.

You may be asked to return to the waiting area if the clinician needs to re-check the eye pressure about an hour after the laser. You will be sent home with relevant advice. Keep in mind your vision may be a little blurred, but this usually settles within a few hours following treatment.

When will I have a follow up appointment?

You will be reviewed in the outpatient department about 4 to 6 weeks after your laser treatment.

In a small number of patients, eye pressure might be elevated after the laser procedure. If this is the case, clinician will decide if you need to be booked for a sooner follow-up appointment.

Complications of SLT

SLT is essentially a very safe laser treatment, with only a few transient side effects:

• Elevated eye pressure:

The main risk of SLT is a spike in eye pressure, but this tends to occur during the first few hours after the procedure. Obviously, when the main goal is to lower the pressure, this is undesirable. Fortunately, these elevations in pressure are generally short-lived. Rarely, the eye pressure can remain elevated which then requires additional treatment for control.

• Ocular inflammation (uveitis)

Postoperative inflammation following SLT usually occurs 2 to 3 days following the procedure. The inflammation is usually transient and resolves within a few days.

Patient with a history of ocular inflammation, are not good candidate for SLT as the procedure can cause a flare-up,

• Corneal Oedema

Occasionally, vision may be a little blurry after the laser due to your cornea (the clear window in the front of your eye) swelling.  This is usually temporary but, in a few cases, can require additional treatment.

You will be given drops to help prevent these problems. If your eye pressure rises immediately after the treatment, you may require some additional eye drops or tablets before you can go home.

Uncommon complications:

• Macular Oedema

Retinal side effects are possible following SLT, but they tend to occur in patients with pre-existing retinal problems or underlying systemic conditions, making them more prone these changes occurring.

Post-Laser problems

If you experience any of the following symptoms after your laser treatment, please contact the eye clinic for advice immediately:

• Increasing redness of your eye
• Excessive or worsening pain
• Loss of vision

Please contact the Eye Clinic if you need any further advice on telephone tel: 01482 816658 or tel: 01482 608788 (8.30 am to 5.00 pm) or

Out-of-Hours tel: 01482 604346 (Please listen to full voice message on how to access emergency out of hours service).

Should you require further advice on the issues contained in this leaflet, please do not hesitate to contact the Ophthalmology Department on tel: 01482 816658.