Date of Degree
8-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Program
Vision Science
Advisor
Brian K. Foutch
Advisor
Jeffrey C. Rabin
Advisor
Michelle T. Aaron
Advisor
Michael L. Denton
Abstract
Excess optical radiation can injure the retina through either rapid heat deposition (photothermal damage) or cumulative photo‑oxidative stress (photochemical damage), yet current laser‑safety limits treat these mechanisms as independent. To test that assumption, this dissertation integrated systematic wavelength, duration and temperature‑controlled laser exposures with live/dead fluorescence imaging in a melanin‑loaded hTERT‑RPE1 monolayer model. First, concurrent 447 nm (blue) and 2 µm (infra‑red) beams delivered for 200 s demonstrated a strong thermal–photochemical synergy: each beam alone was sub‑threshold (≤25 % lethality) but together produced 100 % RPE death without exceeding 50 °C, proving that modest heating markedly lowers the photon dose required for photochemical injury. Second, continuous‑wave thresholds were mapped at 413, 447 and 488 nm over 0.25–400 s. All three wavelengths exhibited two‑segment ED₅₀ curves: steep, time‑dependent irradiance at short exposures (photothermal damage) followed by wavelength‑specific plateaus that obey intensity–time reciprocity (photochemical damage). Plateau radiant‑exposure values increased with wavelength (0.94, 2.1 and 4.2 kJ cm⁻², respectively), and the photothermal–photochemical crossover shifted later in time from 413 nm (~60–100 s) to 488 nm (>120 s), confirming a weighted action spectrum with shorter wavelengths. Together these results show that (i) sub‑threshold heating can amplify blue‑light photochemical toxicity, and (ii) photochemical reciprocity limits are wavelength‑dependent rather than fixed. Although derived from an isolated RPE layer in vitro, the data indicate that ANSI Z136.1 dual‑limit exposure criteria may underestimate retinal risk when moderate temperature rises coincide with short‑wavelength light. The work provides quantitative benchmarks for refining mixed‑mechanism safety models and guides future in vivo validation of wavelength‑ and temperature‑dependent retinal hazards.
Recommended Citation
Ha, Jin B., "Advanced Interactions of Directed Energy with Retinal Pigment Epithelial Cells and Their Photochemical and Photothermal Responses" (2025). Theses & Dissertations. 471.
https://athenaeum.uiw.edu/uiw_etds/471
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