Scaling law analysis of the 577 and 810 nm parameters compared by Vujosevic et al.
45 finds the TR of 810 nm 6X wider than for 577 nm (1.82 vs. 0.29 watts) (
Table 2).
45 This reflects the higher energy and RPE melanin absorption of 577 nm compared with 810 nm.
39,51 By treating at Ω HSP < 1.0, the safety margin of the 810 nm settings examined becomes larger than the TR (1.92 watts), increasing treatment safety. In contrast, exceeding an Ω HSP of 1.0 by 2.59X, the safety margin of the 577 nm parameters becomes less than the TR, falling to just 0.20 watts, making the safety margin of the 810 nm parameters employed by Vujosevic et al.
45 9.6X larger (and thus safer) than the 577 nm parameters (
Tables 1 and
2). Thus compared with 810 nm, 577 nm is more likely to cause inadvertent retinal damage; such as might result from titration with a faulty titration algorithm or misestimation of test-burn intensity, incorrect laser settings, individual patient or local retinal variations in RPE melanin density or heterogeneity, or media absorption or scatter.
40 Clinically, this is illustrated by the fact that it is difficult if not impossible to burn the retina with current 810 nm lasers pulsed at a 5% DC, whereas it is easily done with 577 nm (
Fig.).
21,30,40 Illustrating these principles is a recent multicenter clinical trial comparing low-duty cycle (5%) micropulsed 810 nm laser to half-dose photodynamic therapy for central serous chorioretinopathy (CSR).
30–32 Despite inadequate, and thus ineffective micropulse laser treatment in that study, the 810 nm laser power used (1.80 watts) was markedly higher than that used by Vujosevic et al.
45 (0.75 watts).
23,30–32,45 As a clinical demonstration of the very wide TR/safety margin of low frequency pulsed 810 nm, no LIRD was reported by investigators in the CSR trial.
30 Our calculations suggest that increasing the Vujosevic et al.
45 577 nm power a similar degree (2.4X) would have resulted in retinal burns, and possibly visual loss.