Effect of ambient temperature and intracellular pigmentation on photothermal damage rate kinetics

Computational models predicting cell damage responses to transient temperature rises generated by exposure to lasers have implemented the damage integral ([Formula: see text]), which time integrates the chemical reaction rate constant described by Arrhenius. However, few published reports of empirical temperature histories (thermal profiles) correlated with damage outcomes at the cellular level are available to validate the breadth of applicability of the damage integral. In our study, an analysis of photothermal damage rate processes in cultured retinal pigment epithelium cells indicated good agreement between temperature rise, exposure duration ([Formula: see text]), and threshold cellular damage. Full-frame thermograms recorded at high magnification during laser exposures were overlaid with fluorescence damage images taken 1 h postexposure. From the image overlays, pixels of the thermogram correlated with the boundary of cell death were used to extract threshold thermal profiles. Assessing photothermal responses at these boundaries standardized all data points, irrespective of laser irradiance, damage size, or optical and thermal properties of the cells. These results support the hypothesis that data from boundaries of cell death were equivalent to a minimum visible lesion, where the damage integral approached unity ([Formula: see text]) at the end of the exposure duration. Empirically resolved Arrhenius coefficients for use in the damage integral determined from exposures at wavelengths of [Formula: see text] and 532 nm and durations of 0.05–20 s were consistent with literature values. Varying ambient temperature ([Formula: see text]) between 20°C and 40°C during laser exposure did not change the [Formula: see text]-dependent threshold peak temperature ([Formula: see text]). We also show that, although threshold laser irradiance varied due to pigmentation differences, threshold temperatures were irradiance independent.