A model for light toxicity of cultured human retinal pigment epithelium

Background: The effect of visible light on human retinal pigment epithelial (HRPE) cells has not been characterized under conditions that provide strict thermal control. Methods: HRPE cells were isolated and grown to confluence. Cells were exposed to light in an incubator in which the cell temperature was controlled in response to a temperature sensor maintained in the tissue culture medium. Cells were exposed: (A) for 24, 36, and 48 h; and using a 24-h exposure followed by 24 h darkness; (B) at varying intensities of light using neutral density filters; (C) under a yellow filter; and (D) with a 12-h on-off cyclic light. Results: (A) Light exposure of 36 and 48 h resulted in significant cytotoxicity, while the initial 24-h exposure did not induce subsequent cytotoxicity. (B) Light irradiance levels from 43 to 54 mW/cm² were required to demonstrate cytotoxicity. (C) Use of a yellow filter did not eliminate the observed cytotoxicity. (D) Cyclic exposure did not result in significant cytotoxicity. Conclusion: This study establishes a model and basic parameters of light toxicity to HRPE cells in vitro using strict temperature control that may be used to evaluate photochemical injury to HRPE cells.