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J. Roider, S. Koinzer, K. Schlott, M. Bever, L. Pataszynski, R. Birngruber, R. Brinkmann; Predictable Retinal Photocoagulation by Automated, Temperature-Related Exposure Control: Experimental and Clinical Results. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5043.
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Dosimetry in retinal photocoagulation is done by choosing the appropriate power setting according to the desired level of retinal whitening. This technique is not very accurate and appropiate because laser power can only be evaluated after the spot has already been applied. We developed a device that measures retinal temperature rise in real time during the laser exposition. It automatically computes the laser settings for every laser spot separately, keeping the same horizontal and vertikal damage extent of every spot applied. This method tries to to prevent over- or undertreatment in e.g diabetic maculopathy and to reduce patient pain during the treatment of panretinal photocoagulation
Short ns laser pulses (527 nm, 75 ns, 1kHz) were repetitively applied additionally during standard photocoagulation of the retina to excite acoustic waves by thermo-elastic expansion, which were recorded by an ultrasonic transducer integrated in the laser contact lens. Since this signal is modulated by temperature changes in the retina, real time temperature measurement of the retina is possible. Based on this opto-acoustic signal, an algorithm was developed to predict exposure times necessary to produce a certain extent of laser damage. The laser device shuts off automatically, when the necessary exposure time had passed. This method was applied to rabbit eyes and evaluated by fundus photography and morphometry, FA and histology.
Very homogeneous spot morphologies could be achieved over a wide range of laser power settings, compared to the same laser settings with pre-defined exposure times both in rabbits . The system works both with a fixed mechanical contact lens, but also with manual positioning of the contact lens. Comparing a series of laser spot with automatic dosimetry to those without dosimetry, the former had even diameters and low standard deviations of the horizontal spot extent. These findings were confirmed by histological specimens.
The horizontal spot extent could be controlled effectively by optoacoustic laser dosimetry. The method introduced is of clinical imprtance in appling gentle laser effects to the retina, since it prevents over- and undertreatment at every spot applied. Consequently collateral damage to delicate retinal layers does not occur, making treatment safer and also less painful.
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