Laser-tissue interactions in retinal photo-thermal therapy : mechanisms and applications
- Since its introduction nearly 40 years ago, laser photocoagulation has been the standard of care for treatment of numerous retinal pathologies. Recently, new approaches have been introduced for more selective targeting of various retinal layers, including patterned scanning photocoagulation, selective retinal therapy, and sub-lethal treatment. Despite its broad use in clinical practice, there remains a need for the quantitative description of laser-tissue interactions involved in retinal phototherapy. A unified description of various treatment regimes and associated mechanisms of tissue damage would allow for optimization of laser parameters to improve selectivity and safety of retinal photocoagulation, and for avoidance of undesirable collateral damage. The presented work describes an investigation into the dynamics of the retinal response to hyperthermia and vaporization. A finite-element computational model of photocoagulation and rupture was constructed based on experimental measurements of laser interactions with tissue, and verified in vivo in the millisecond time domain. Two approaches towards improvement of tissue heating uniformity were studied: spatial and temporal modulation of the treatment beam. After optimization using the computational model, beam shaping and pulse modulation systems were constructed. Experimental studies in vivo confirmed improvements in safety of the retinal treatment, potentially allowing for reductions in treatment time, thermal damage extent, and perceived pain. In addition, tissue response to sub-lethal thermal stress in the retina was explored using expression of heat shock protein in an animal model. Computational modeling of the corresponding treatment regime demonstrated that a similar response is likely to occur in clinical application of sub-lethal exposures. Photo-mechanical interactions in the retina were investigated in model systems and in vivo with microsecond-range exposures. The dominant mechanisms of tissue damage were identified and the corresponding limits of the safe therapeutic window were computed over a broad range of pulse durations - from microseconds to seconds. An understanding of the thermal and mechanical interactions involved in laser heating of the retina allows for the realization of safer and more selective treatment regimes. All three mechanisms investigated in the current study -- photocoagulation, photomechanical interactions and sub-lethal hyperthermia -- play a role in clinical treatment. The developed quantitative models of these interactions have immediate applicability to clinical practice, providing guidance towards optimization of retinal phototherapy, evaluation of retinal safety, and development of new clinical applications.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Sramek, Christopher Koerner
|Stanford University, Department of Applied Physics
|Blumenkranz, Mark S
|Blumenkranz, Mark S
|Statement of responsibility
|Christopher Koerner Sramek.
|Submitted to the Department of Applied Physics.
|Thesis (Ph. D.)--Stanford University, 2010.
- © 2010 by Christopher Koerner Sramek
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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