Temperature Increase and Damage Extent at Retinal Pigment Epithelium Compared between Continuous Wave and Micropulse Laser Application

Continuous wave (CW) and microsecond pulse (MP) laser irradiations were compared
regarding cell damage and laser-induced temperature rise at retinal pigment epithelium (RPE). The
RPE of porcine RPE-choroid-sclera explants was irradiated with a 577 nm laser inCWor MP mode (5%
or 15% duty cycle (DC)) for 20 ms or 200 ms at an average laser power of 20–90mW. Cell viability was
investigated with calcein-AM staining. Optoacoustic (OA) technique was employed for temperature
measurement during irradiation. For 200 ms irradiation, the dead cell area (DCA) increased linearly
(1600 m2/mW) up to the average power of 40 mW for all modes without significant difference.
From 50 mW, the increase of DCA of MP-5% significantly dropped to 610 m2/mW (p < 0.05), likely
due to the detected microbubble formation. OA temperature measurement showed a monotonic
temperature increase in CW mode and a stepwise increase in MP mode, but no significant difference
in the average temperature increase at the same average power, consistent with the temperature
modeling. In conclusion, there is no difference in the average temperature rise between CW and MP
modes at the same average power regardless of DC. At lower DC, however, more caution is required
regarding mechanical damage due to microbubble formation.