gms | German Medical Science

Background: Retinal photocoagulation is the established gold standard to treat different central and peripheral retinal disorders. Conventional laser power control by judgement of retinal whitening is only possible in retrospect and is not very accurate. Real-time retinal temperature measurement during coagulation facilitates a temperature-feedback exposure time control for each individual spot, granting defined and homogenous strength of fundus lesions.

Method: Retinal temperature measurement in real time is realized by optoacoustics. Short probe laser pulses elicit temperature-dependent thermoelastic pressure waves of the retina and retinal pigment epithelium, that are detected by an ultrasonic transducer in the contact lens. A series of temperature plots for spots with varying exposure times and laser powers was generated, and by probit blot analysis the probability to achieve a clinically visible spot at a given early temperature rise could be determined. Based on these data, an algorithm was computed that shuts off the treatment laser when a defined coagulation effect is achieved. This algorithm was tested on rabbit eyes in vivo.

Results: Automatic temperature-feedback exposure time control allows the application of homogenous laser lesions over a wide power range, where conventional constant exposure times produce growing spot diameters with increased power. Temperatures during photocoagulation reached values of 50°C to 80°C.

Conclusions: This new method allows automatic laser effect control that generates homogenous fundus lesions during retinal photocoagulation in rabbits. For a next step, the same method should be applied to human eyes with inter- and intraindividually variable transmissions and absorptions, aiming to achieve even and defined lesions and thus avoid extraneous tissue damage and pain.