Thermal Interaction between laser & tissue during retinal photocoagulation

The conventional retinal photocoagulation uses continuous wave (CW) lasers which results in pathophysiologic thermal environment to surrounding normal tissues such as neural retina, choroid, and photoreceptors. Selective photodamage of retinal pigment epithelium (RPE), thus sparing photoreceptors can be achieved by using short pulsed lasers. The problem associated with the usage of short pulsed laser is that it is difficult to determine correct dosimetry parameters. The aim of this study is to quantify the influence of different laser parameters over the therapeutic range and to find their optimum values in order to achieve the selective retinal treatment. The present study investigates the laser-tissue interaction by analyzing the transient temperature rise in ocular tissues during repetitive laser photocoagulation. The absorption coefficients based on combined scattering and absorption characteristics for ocular tissues such as vitreous humour, neural retina, RPE, choroid, and sclera are accounted in order to get accurate temperature rise. The laser parameters: wavelength, pulse width, and the laser profile are critical in determining the selective damage. The temperature rise in the neural retina and RPE are quantified by varying the laser parameters. Results reveal that microsecond (μs) pulsed lasers with green wavelength and Gaussian heat source profile is the most effective in selective treatment.