Background: A diode laser can be used to create a subthreshold (invisible end point) lesion in patients with age-related macular degeneration (AMD). This has the potential benefit of localizing the treatment effect to the retinal pigment epithelium and sparing more of the overlying sensory retina. We performed a study to compare the safety and efficacy of argon laser and subthreshold infrared (810-nm) diode laser macular grid photocoagulation in reducing the number of drusen in patients with AMD.
Methods: We reviewed the charts of 144 patients with bilateral early-stage nonexudative AMD, characterized by soft drusen. One eye of each patient was treated, and the other eye served as a control. Seventy-eight eyes of 78 patients with a mean age of 67.5 (standard deviation [SD] 8.3) years underwent argon laser macular grid photocoagulation at a university-affiliated hospital in Bologna, Italy, and 66 eyes of 66 patients with a mean age of 66.4 (SD 6.3) years underwent subthreshold infrared (810-nm) diode laser macular grid photocoagulation at a private clinic in Bologna. Each group was classified into three subgroups based on the number of drusen (more than 20, 10 to 20, or less than 10). The patients underwent fluorescein angiography, fundus examination, measurement of far (Snellen chart) and near (Jaeger chart) best corrected visual acuity, and visual field and contrast sensitivity testing. The mean length of follow-up was 18 (SD 0.5) months.
Results: At 18 months, far and near best corrected visual acuity were statistically significantly improved in the treatment groups compared with the untreated group (p < 0.001, Mann-Whitney U test). There was no significant difference in visual acuity between the treatment groups. Compared with baseline, the number of drusen was significantly reduced in both treatment groups (p < 0.001). Evolution of the disease was observed in the untreated group. The visual field was slightly but significantly reduced after argon laser treatment (p < 0.001) but not diode laser treatment; the difference in visual field between the two groups was not significant. There was a slight reduction in contrast sensitivity, particularly with night vision, after argon laser treatment but not diode laser treatment. The difference between the two treatment groups was significant (p < 0.01).
Interpretation: Subthreshold infrared diode macular grid photocoagulation may be a safe and viable method for preventing progression of nonexudative AMD.