The study is a prospective randomised controlled intervention comparing the intraocular pressure outcomes following Selective Laser Trabeculoplasty (SLT) treatment of 180 degrees SLT compared to 360 degrees in treatment naive patients with bilateral ocular hypertension or primary open angle glaucoma . The right eye of each patient will be randomised to receive either 180 or 360 degrees SLT, while the fellow eye will receive the opposite treatment. That is, if the right eye is randomised to 180 degrees SLT, then the left eye will receive 360 degrees SLT.

The primary objective is to assess the mean difference in intraocular pressure between two eyes of each participant. The mean difference in IOP will be assessed at two weeks and at one, three and six months after treatment with SLT.

Secondary outcomes include assessing whether there are differences in visual acuity, anterior chamber inflammation, visual field progression and the rate of complications between the two eyes treated with either 180° or 360° of selective laser trabeculoplasty. The complications assessed are those published in the literature including: pain, blurred vision, anterior chamber inflammation, IOP spike, and hyphaema. Additionally, participants will be given the opportunity to report symptoms experienced through free text.

Potential patients will be identified by the Principal Investigator during a clinic visit. Pre-screening criteria is carried out by the co-investigator or the research co-ordinator. General eligibility criteria, inclusion and exclusion criteria are applied. The Research Co-ordinator approaches the patient and the SLT laser study is discussed with the patient. The patient is provided the Information Sheet and advised to contact the Research Coordinator if they wish to proceed. Informed consent is obtained if the patient wishes to proceed. Baseline data is collected and the right eye is randomised with the fellow eye to receive non randomised treatment.

SLT is performed in both eyes (180 degrees in 1 eye + 360 degrees in the fellow eye) during an office visit. IOP in both eyes is checked and recorded at one hour post treatment.

The patient returns for follow up at two weeks post SLT treatment visit. A complete ocular examination, including IOP, is undertaken. Complications and adverse events are assessed and recorded. Any change to eyedrops is recorded. Patients return at one, three and six months for review, and the same assessment as above is undertaken at each visit.

Enrolling is complete when 48 patients are enrolled. Patients are advised enrolling is complete.

Statistical analysis is undertaken to assess the mean change in IOP between the two treatments. Complications and adverse events are each treatment group are recorded. The study is submitted for publication and written communication is provided to each enrolled patient.

Inclusion Criteria:

• Age greater than 18 years
• IOP greater than 21mmHg (millimetres mercury)
• Glaucoma suspect
• Open angle glaucoma - primary or secondary
• Bilateral disease
• History of previous uncomplicated cataract surgery
• Willingness to be treated with selective laser trabeculoplasty
• Willingness to participate in the study, along with signed written consent

Exclusion Criteria:

• Age younger than 18 years
• Paediatric glaucoma
• Narrow or closed angles on gonioscopy
• History of ocular trauma
• Active or history of uveitis
• History of amblyopia
• History of, or, current steroid use - ocular, periocular or systemic
• History of any prior ocular laser - Argon laser trabeculoplasty (ALT), SLT or retinal laser
• Monocular patient
• Active proliferative diabetic retinopathy
• History of complicated cataract surgery
• Recent cataract surgery - within the last six months
• Unable to consent for treatment