Thermal interaction of multi-pulse laser beam with eye tissue during retinal photocoagulation: Analytical approach

- Generalized thermal model of a laser irradiated lamellar media with arbitrary number of layers is proposed.
- The model is used for description of thermal disturbance in eye fundus during retinal photocoagulation.
- Risks of retina overheating due to uncertainty in eye tissue properties are evaluated.
- Both Gaussian and top-hat lasers with different wavelengths are considered.
- The model is validated against theoretical and experimental data available in the literature.

The laser-induced temperature disturbance within retinal pigmented epithelium (RPE) and in the adjacent layers of a human eye is studied with the aim to specify laser optimal parameters providing safe treating. Proposed is a generalized model of a laser irradiated multi-layered media with arbitrary number of layers having uniform thermal and discrete optical properties. An analytical approach is used that allowed obtaining description of the spatial and temporal evolution of the temperature in the irradiated media. The required maximum temperature is kept as a preassigned value, and the search for necessary laser parameters is subjected to this condition. Calculations are made for Gaussian and uniform (top hat) lasers with wavelengths 514, 532 and 577 nm. Necessary combinations of pulse power and its duration that provide predetermined peak temperature within RPE are identified. The possible inter-individual deviations of eye physical properties are reviewed and probable risks of RPE overheating arising from these uncertainties are evaluated for the first time. The advanced concept of sub-threshold multi-pulse laser treatment is analyzed. The method for definition of necessary pulse train parameters for maintaining the target RPE temperature at the end of the pulse train is proposed. Analytical model is validated in a wide range of laser parameters against state-of-the-art theoretical and experimental data available in the literature.