Abstract
Purpose :
Subvisible, non-damaging retinal laser treatments are currently used for several retinal diseases. Due to strong inter- und intraocular variations of light scattering and pigmentation at the fundus the laser-induced temperatures differ widely. In order to overcome these uncertainties we developed an optoacoustic (OA) method allowing to determine and control the temperature rise during treatments. For treatment the currently used green and yellow wavelengths primarily address the retina and the retinal pigment epithelium (RPE) due to the strong melanin absorption in the RPE. The involvement of the choroid in the pathogenesis of chorioretinal diseases has been increasingly recognized, and the choroid is now being discussed as a target for treatment. Since IR wavelength are well suited for a choroidal thermal stimulation, this work attempts a combination of green and IR wavelength to achieve non-damaging stimulation of the retina, RPE and also the choroid with a proper temperature control.
Methods :
Porcine RPE/choroid/sclera explants were placed in a cuvette filled with physiological saline solution. The specimen were irradiated via a laser slitlamp by a Q-switched Nd:YLF-laser (1053 nm and 527 nm wavelength) with a repetition rate of 10 kHz and pulse duration of 50 ns for 100 ms on a spot diameter of 200 µm. Acousto-optic modulators were used to modulate the laser pulse energies and clock ratio of the two wavelengths. OA transients induced by each laser pulse were recorded with an ultrasonic transducer embedded in a contact lens for temperature monitoring.
Results :
OA transients were detected for every laser pulse of both wavelengths. Their ratios indicated a stronger absorption behind the RPE when combining both wavelengths compared to the 527 nm applied alone. For example, under the same average power of 35 mW, the maximum temperature of the RPE was measured to be 58,4 °C when irradiating with 527 nm and 3,5 µJ pulse energy, compared to 34,9 °C when 527 nm and 1053 nm were combined with 2,5 µJ and 4,5 µJ pulse energy, respectively, at 1:1 clock ratio.
Conclusions :
This study is a first step towards a deeper thermal stimulation of the retina, RPE and choroid under proper temperature control. Future work will focus on temperature estimation at the choroid by the IR pulses. Further a feedback controlled irradiation with proper active temperature control will be implemented.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.