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C. M. Floehr, J. Kandulla, K. Herrmann, J. Stalljohann, J. Sandeau, G. Apiou-Sbirlea, R. Brinkmann, R. Birngruber, J. Roider; Influence of Choroidal Perfusion on Retinal Temperature Increase During Cw Laser Irradiation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2269.
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© ARVO (1962-2015); The Authors (2016-present)
In retinal laser treatments the therapeutic effect is initiated by a transient temperature increase. The retinal temperature is influenced by differences in pigmentation and transmission of the ocular media. Another factor, important in Transpupillary Thermotherapy (TTT), is choroidal blood flow. Ocular Perfusion acts as a heat dissipating mechanism when heat is externally applied. Individual differences in ocular perfusion can lead to an under- or overdosage of the regarded temperature increase. Aim of this work is to quantify the influence of choroidal perfusion on the retinal temperature increase during cw laser treatments. The experimental obtained data are compared to numerical temperature simulations.
The experiments are performed in-vivo on rabbits (Chinchilla Bastard). The retinal temperature increase of less than 12 K is achieved by applying the radiation of a TTT-laser ( = 810 nm) for 1 minute on a 2 mm spot. Optoacoustic techniques are used to determine the temperature increase during the irradiation. For a reduction of the choroidal perfusion, the intraocular pressure (IOP) is increased stepwise from 20 mmHg to 120 mmHg resulting in higher temperature increases. Additionally the rabbit is sacrificed after the last experiment, to eliminate the influence of choroidal blood flow. For an estimation of the perfusion rates, the data are compared to numerical temperature simulations based on two absorbing layers (RPE and choroid) and taking into account choroidal perfusion.
The results are very much dependent on the individual rabbit. In one rabbit a retinal temperature increase of roughly 5 K was found by applying laser irradiation with a retinal irradiance of 4.7 W/cm2. On the same rabbit an increase of 12 K was found post mortem, which means an increase of 140 %. The temperature data obtained by increasing the IOP are mainly within this range.
These first measurements demonstrate the high influence of choroidal perfusion on retinal temperature increases during long exposure laser treatments. As the individual perfusion rate can not be quantified before a treatment, a dosimetry control, based on an online determination of retinal temperature increases, is necessary to enhance the safety of retinal cw laser treatments.
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