Damage Processes in Extended Laser Exposures Using an In Vitro Retinal Model

Nathaniel J Pope¹Jin Ha²Madeline E Melzer^1,3Priscilla Lopez⁴Amanda Tijerina⁵Harvey H Hodnett¹Matthew Macasadia¹Gary D Noojin⁶Michael Lee Denton^6*

• ¹Science Applications International Corporation (United States), McLean, Virginia, United States
• ²Rosenberg School of Optometry, University of the Incarnate Word, San Antonio, Texas, United States
• ³Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
• ⁴Department of Biomedical Engineering and Chemical Engineering, Klesse College of Engineering and Integrated Design, University of Texas at San Antonio, San Antonio, Texas, United States
• ⁵Conceptual Mindworks (United States), San Antonio, Texas, United States
• ⁶Air Force Research Laboratory, Dayton, United States

Retinal pigment epithelial (RPE) cells are sensitive to both photothermal and photochemical damage when exposed to lasers with wavelengths associated with the retinal blue light hazard. Laser power density (irradiance) and exposure duration primarily dictate the damage mechanism. Relatively high irradiances and short exposure durations typically lead to melanin-dependent photothermal damage, whereas low irradiance and long duration exposures are required for photochemical pathways. However, little is known about damage mechanisms at intermediate irradiances and durations for pigmented cells. The current Z136.1-2022 laser safety standard from the American National Standards Institute (ANSI) does not consider combined photothermal and photochemical damage processes. In addition, the ANSI Z136.1 standard classifies photochemical damage as nonthermal. Here, we use extended laser exposure parameters in an in vitro RPE cell model to show that elevated temperatures accelerate photochemical damage mechanisms. In addition, for 447-nm exposure conditions leading to damage considered neither purely photothermal nor photochemical, there is a reduced requirement for the thermal component for cell death. Our results suggest the need to address safety for lasers with blue wavelength emission, as in ophthalmic devices for example.