Purchase this article with an account.
R. Brinkmann, J. Kandulla, H. Elsner, J. Sandeau, G. Apiou–Sbirlea, J. Roider, R. Birngruber; Influence Of Pigmentation And Perfusion On The Temperature Increase During Retinal Laser Treatments . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2158.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Even though being crucial for the therapeutic effect in a variety of retinal laser treatments, the induced temperature increase at the treatment spot is not exactly known due to individually different tissue properties. Beneath the pigmentation, the vascular density and perfusion play a major role especially in long term irradiations like tumor treatment, TTT and PDT. In TTT a too low temperature increase might result in no therapeutic benefit while high temperatures have shown to result in extended retinal photocoagulation and visual loss. After demonstration of a non–invasive realtime temperature evaluation method by optoacoustics in recent years, the role of pigmentation and perfusion was investigated in detail by in–vivo experiments as well as analytical and numerical modeling.
Rabbit eyes in–vivo were irradiated with a diode laser (=810nm, P≤3W) for 60s to simulate TTT. Simultaneously, pulses from a N2–laser pumped dye laser (=500nm, τ=3.5ns, E≈5µJ) were applied onto the retina for optoacoustic temperature monitoring. The absorption of a laser pulse leads to heating and subsequent thermoelastic expansion of the tissue, causing the emission of a pressure wave, which is temperature dependent. The pressure wave is detected by an ultrasonic transducer embedded in a contact lens. Analytical and numerical models are developed to investigate especially the role of a global as well as layer restricted heat sink. Perfusion is experimentally varied by changing the intraocular pressure and by sacrifying the animal.
By applying the IR–irradiation on a spot diameter of 2 mm, a temperature increase of 1.4 °C/(W/cm2) after 60 s was found in living rabbit eyes. This value correspeonds quite well to a global perfusion rate of 0.13 s–1. After sacrification of the animal we determined a higher temperature increase of 2.2 °C/(W/cm2) at the same location due to the absence of perfusion. The influence of differently pigmented eyes and different intraocular pressures will be presented in detail.
The strong influence of choroidal perfusion on the retinal temperture increase during laser treatments could be demonstrated. Due to the strong variation of inter and intraindividual absorption and perfusion especially on pathological sites, a temperature monitoring seems absolutely be neccesary in long term laser irradiations, for safety reasons as well as for an optimal therapeutic outcome.
This PDF is available to Subscribers Only