Abstract
Purpose: :
To study the fundamental mechanisms of laser damage and the associated morphological changes to the retina.
Methods: :
Retinal laser lesions were produced in a total of five eyes from three Cynomolgus monkeys (Macaca fascicularis) over the wavelength range of 555 nm to 570 nm and with a pulse width of 1.5 microseconds. To produce the lesions, a flash lamp pumped dye laser (Model LFDL-8; Candela Corporation; Wayland, MA) was coupled into a multimode fiber optic the output of which was co-aligned with two high-resolution Adaptive Optics enhanced imaging systems. The imaging systems, cSLO (Iris Adaptive Optics; Berkeley, CA) and SDOCT (PSI Inc.; Andover, MA), collected serial images concurrently with laser exposures at 30 frames per second (fps) and 13 fps, respectively. For laser exposures, the fiber optic laser delivery system was configured to deliver either a 9 milliradian or 3 milliradian beam divergence resulting in geometric spot sizes on the retina of approximately 170 microns and 60 microns, respectively. Laser pulse energy was increased from just below the expected threshold for funduscopically observable damage to approximately three times this value.
Results: :
Threshold for minimum funduscopically visible damage was consistent for similar laser beam parameters previously reported in rhesus monkey. SDOCT images suggest damage originates in the RPE, with morphological disruption evident both anterior in the photoreceptor layer and posterior in the choroid. Images collected with cSLO indicate a general change in reflectance consistent with thermal denaturation at larger retinal spot sizes and violent disruption of the retinal surface consistent with explosive vaporization for the smaller spot size.
Conclusions: :
There appears to be a transition in damage mechanism from thermal denaturization to photomechanical disruption as a function of the irradiance available at the retina for wavelengths between the 555 nm- 570 nm and pulse durations on the order of 1 microsecond.
Keywords: laser • imaging/image analysis: non-clinical • retina