June 2023
Volume 64, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2023
A Computational Model of Retinal Expansion during Laser Irradiation
Author Affiliations & Notes
  • Madhusudhanan Balasubramanian
    Electrical and Computer Engineering, The University of Memphis, Memphis, Tennessee, United States
  • Jabia Chowdhury
    Electrical and Computer Engineering, The University of Memphis, Memphis, Tennessee, United States
  • Footnotes
    Commercial Relationships   Madhusudhanan Balasubramanian None; Jabia Chowdhury None
  • Footnotes
    Support  None
Investigative Ophthalmology & Visual Science June 2023, Vol.64, 1803. doi:
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      Madhusudhanan Balasubramanian, Jabia Chowdhury; A Computational Model of Retinal Expansion during Laser Irradiation. Invest. Ophthalmol. Vis. Sci. 2023;64(8):1803.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : During laser irradiation, elevated kinetic energy of constituent water molecules and other macromolecules in the posterior segment cause thermal expansion leading to changes in its structure and density. We present a computational multiphysics model to accurately capture the photothermal and thermomechanical changes in the posterior segment during laser irradiation.

Methods : We develoepd a multiphysics model of light-tissue interaction that accounts for changes in thermal and optical characteristics of retinal tissues during laser irradiation. Temperature-dependent thermal expansion α(T) and thermal conductivities κ(T) of retina, RPE, choroid and sclera were assumed to follow those of water. Thermal conductivity at retinal locations with temperature above 383.15 K was assumed to be that of water vapor. Arrhenius damage intergral was used to continuously monitor locations of tissue damage and vary their optical characteristics. In coagulated locations, optical absorption and scattering coefficients, respectively, were set to 36% lower and 598.3% higher than those of undamanged tissues. With the posterior segment modeled as linearly elastic solids, governing equations of bioheat transfer were coupled with those of soft tissue structural dynamics. For validation, ex vivo porcine retinas were irradiated with a 200 mW 532nm laser until thermal expansion was observed using optical coherence tomography (OCT). Computational estimates of irradiation pattern and structural deformation due to laser irradiation were compared with experimental OCT observations.

Results : The computational models of laser transport and retinal irradiance indicated significant differences in irradiance patterns when thermal properties varied with temperature and when optical properties varied with thermal damage. We further observed that the thermal expansion due to photothermal stress accounted for only a smaller portion of observed tissue expansion.

Conclusions : Our computational models confirmed the importance of incorporating time-dependent thermal and optical characteristics in light-tissue interaction models of the retina during laser irradiation. These two factors, however, did not fully explain the extent of retinal expansion observed in ex vivo porcine eyes using OCT. A significant portion of retinal expansion observed during longer irradiation is likely due to material phase changes such as vaporization, bubble formation and condensation.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.

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