Abstract: The update of this review found two additional studies, totaling 11 studies that randomised 2159 participants (3580 eyes) and followed them up to two years, of which six studies (1454 participants) included people with one eye randomised to treatment and one to control. Studies were conducted in Australia, Europe and North America. Overall, the risk of bias in the included studies was low, particularly for the larger studies and for the primary outcome development of CNV. Photocoagulation did not reduce the development of CNV at two years' follow-up (odds ratio (OR) 1.07, 95% confidence interval (CI) 0.79 to 1.46, 11 studies, 2159 participants (3580 eyes), high quality evidence). This estimate means that, given an overall occurrence of CNV of 8.3% in the control group, we estimated an absolute risk reduction by no more than 1.4% in the laser group, according to the lower CI limit. Only two studies investigated the effect on the development of geographic atrophy and could not show a difference, but estimates were imprecise (OR 1.30, 95% CI 0.38 to 4.51, two studies, 148 participants (148 eyes), low quality evidence). Among secondary outcomes, photocoagulation led to drusen reduction (OR 9.16, 95% CI 6.28 to 13.4, three studies, 570 participants (944 eyes), high quality evidence) but was not shown to limit loss of 3 or more lines of visual acuity (OR 0.99, 95% CI 0.81 to 1.22, nine studies, 2002 participants (2386 eyes), moderate quality evidence). In a subgroup analysis, no difference could be shown for conventional visible (eight studies) versus subthreshold invisible (four studies) photocoagulation for the primary outcomes (P value = 0.29). The effect in the subthreshold group did not suggest a relevant benefit (OR 1.27, 95% CI 0.82 to 1.98). No study used micropulse subthreshold photocoagulation. No other adverse effects (apart from development of CNV, geographic atrophy or visual loss) were reported. The trials included in this review confirm the clinical observation that laser photocoagulation of drusen leads to their disappearance. However, treatment does not result in a reduction in the risk of developing CNV, and was not shown to limit the occurrence of geographic atrophy or visual acuity loss. Ongoing studies are being conducted to assess whether the use of extremely short laser pulses (i.e. nanosecond laser treatment) cannot only lead to drusen regression but also prevent neovascular AMD.

Plain-language summary: This review included data from 11 trials conducted in Australia, Europe and North America. The studies followed up 2159 participants with drusen (3580 eyes) to two years, of which six studies (1454 participants) included people with one eye randomised to treatment and one to control. Four studies (850 eyes) used subthreshold photocoagulation. Three out of four studies using laser subthreshold photocoagulation were sponsored by the laser producer. These studies showed that laser photocoagulation of drusen leads to their disappearance. However, laser photocoagulation of drusen did not reduce the risk of developing CNV, which was about 10% at three years in untreated participants. A smaller number of studies reported on the development of geographic atrophy, that is, atrophy in the centre of the macula, but these studies were inconclusive and the effect of laser treatment of drusen on the development of geographic atrophy was uncertain. The risk of visual loss was similar in treated and untreated groups. There was no suggestion that a benefit may exist with subthreshold photocoagulation. The overall quality of the evidence was high regarding failure to prevent CNV, but it was low for prevention of atrophy due to the small number of participants for whom this outcome was assessed.