Determination of self-focusing effects for light propagating in the eye

Abstract

Recent studies of retinal damage due to ultrashort laser pulses have shown interesting behavior. Supra-threshold hemorrhagic lesions could not previously be produced with high pulse energy, sub-100 fs pulses, leading to the speculation that nonlinear optical phenomena might mediate these effects. To determine what effect self-focusing will have on laser propagation in the eye, we include this nonlinear phenomena in a calculation of the focal plane position and spot size in the eye as a function of incident power. Light is propagated through the components of the eye using ABCD matrices. The nonlinearity is included using the values for the nonlinear refractive indices for ocular components measured in our laboratory and the diffraction term scaling transformation. We examine how nonlinear propagation changes the irradiance at the retina for nanosecond, picosecond and femtosecond laser pulses with pulse energies near the minimum visible lesion (MVL) threshold for retinal damage. We find that self-focusing can substantially decrease the spot size and increase laser irradiance at the retina. We discuss possible effects this might have on retinal damage.