This is a prospective, multicentre, sham-controlled, participant- and assessor-masked superiority trial with two parallel treatment arms which aims to investigate the safety and efficacy of subthreshold nanosecond laser (SNL) in a series of adults with sub-retinal fluid secondary to non-resolving central serous chorioretinopathy (CSCR) by visual and anatomical outcomes. The study population will be individuals with adults (aged 18-70 years inclusive) with non-resolving CSCR (defined as CSCR present for a duration of more than 3 months presenting with either focal or diffuse leakage) who meet all eligibility criteria. 60 subjects total will be enrolled into the study - 40 randomized to receive SNL treatment and 20 to receive sham treatment as per a 2:1 randomization schedule and stratified by type of CSCR (focal vs diffuse). The study has a 24-week study period with five scheduled visits: screening, randomisation (first treatment), 6-week follow up (with second treatment where eligible), 12-week follow-up , 18-week follow-up, and 24-week follow-up. The primary outcome is the proportion of laser-treated study eyes that show resolution of sub-retinal fluid (SRF) as observed on optical coherence tomography (OCT) compared to sham-treated study eyes at 24 weeks. The safety endpoint will be proportion of laser-treated eyes that lose ≥10 letters of of vision (measured on a standard vision chart) compared to sham-treated study eyes and fellow eyes over 24 weeks.