Abstract
Purpose: :
Direct monitoring of the laser–induced effects during retinal treatments such as PDT and TTT might lead to significant improvement of the clinical outcomes. We demonstrate that using polarization sensitive retinal spectral imaging the choroidal and retinal effects can be detected in real time during PDT and TTT.
Methods: :
TTT was performed in rabbits at 790nm, 60 seconds with a 0.86mm retinal spot and power levels of 10–100 mW. PDT was performed in rabbits at the following settings: 689nm, 83 seconds, 600mW/cm2, 2mg Visudyne per kg body weight, exposure started 10 minutes after the injection. The fundus was illuminated with linearly polarized broadband white light (7mW, 2.2 mm spot). The illuminated retina was imaged at cross–polarization in the green spectral range using a cooled CCD camera. During laser exposure the acquired images were stored in a PC for further data analysis.
Results: :
TTT: Laser induced choroidal vasoconstriction could be visualized starting at ∼10% of the laser power that leads to a visible denaturation of the retina. The vasodynamic response became stronger with increased laser power. At irradiances ∼10% below the coagulation threshold a 10–15% decrease in retinal scattering was observed starting within the first 10 seconds of the treatment. Termination of the treatment upon appearance of decreased scattering prevented retinal coagulation. The vasoconstriction did not completely disappear after the laser exposure and was not observed in a euthanized rabbit. PDT: No laser–induced effects have been observed without Visudyne administration. However, during the laser exposure following the Visudyne injection a constriction of the choroidal blood vessels has been seen. Significant inter–animal variability in vascular reaction to the same treatment has been observed.
Conclusions: :
Effects of the laser treatments on choroid and the retina can be visualized non–invasively and in real time by polarization sensitive spectral fundus imaging during TTT and PDT. Further studies are required to correlate the observable retinal changes to the treatment outcomes.
Keywords: laser • photodynamic therapy • age-related macular degeneration