Pulsed laser damage thresholds in vitro for intraocular lenses and membranes

Abstract

Energy and power density damage thresholds were determined in air, for plastic IOL's and membranes at the focal point of several solid-state laser systems: 1) 694 nm, Q -switched single pulse (30 ns), multimode, 2) 1064 nm, Q -switched single pulse (20 ns), TEM 00 , 3) 1060 nm, mode-locked single pulse, 15 ps, TEM 11 , 4) 530 nm, mode-locked single pulse, 15 ps, TEM 11 , and 5) 1064 nm, mode-locked pulse train (9-11 pulses, 30 ps), TEM 00 . Pulse energies bracketing damage thresholds as well as focal diameter and pulse duration for each system were determined. Energy density thresholds are lower, and power density thresholds higher, for shorter duration pulses-e.g., 23 J/cm2(1.15 GW/cm2) versus 6 J/cm2(400 GW/cm2) at the same wavelength as in systems 2) and 3) (p = 0.005). Damage thresholds for glass IOL's are 37 J/cm2(1.9 GW/cm2) and 37 J/cm2(1235 GW/cm2) as in systems 2) and 5). Damage threshold values for plastic membranes (Saran Wrap®) exposed to nanosecond and picosecond pulse trains of Nd:YAG at 1064 nm are about half that of plastic IOL's. When laser pulses with a cone angle of 14° from systems 2) and 5) are focused on plastic membrane next to the IOL, damage thresholds are 30 J/cm2(1.5 GW/cm2) for 20 ns Q -switched pulses and 20 J/cm2(670 GW/cm2) for trains of 30 ps mode-locked pulses. Damage thresholds of IOL's immersed in 0.9 percent saline are approximately the same as those obtained in air.