Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.

We have made an indirect in-vivo determination of spot size focusing in the rhesus monkey model'. Measurements of the laser induced breakdown (LIB) threshold both invitro and in-vivo allow correlation and assignment of a spot size after focusing through the living eye. We discuss and analyze the results and show how trends in minimum visible lesion data should be assessed in light of chromatic aberration. National laser safety standards are based on minimal visual lesion (MVL) threshold studies in different animal models. The energy required for a retinal lesion depends upon many parameters including wavelength and retinal spot size. We attempt to explain trends in reported MVL threshold studies using a model of the eye which allows calculation of changes in retinal spot size due to chromatic aberration. Changes in the MVL threshold are affected by several factors. Three phenomena are known to change the MVL threshold related to spot size: 1) Chromatic Aberration,where the focus moves behind the retina producing larger spot sizes; 2) Melanin Absorption, the absorption of melanin is known to be lower for the near-infrared;3) Ocular Media Absorption, where the absorption increases outside a visible window of 350 rim < X < 1340 nm. In this paper we will investigate the role of changing retinal spot size on the MVL threshold.We have extrapolated the retinal spot size in the rhesus monkey for 580 rim 100 fs laser pulses by correlating the in-vivo LIB threshold with the in-vitro LIB threshold for a 148 SPIE Vol. 2975 • 0277-786X197/$1 0.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/19/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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Recent studies of retinal damage due to ultrashort laser pulses2'3 have shown that less energy is required for retinal damage for pulses shorter than one nanosecond. Laser minimum visible lesion (MVL) thresholds for retinal damage from ultrashort (i.e. < 1 ns) laser pulses are produced at lower energies than in the nanosecond (ns) to microsecond (ps) laser pulse regime. We review the progress made in determining the trends in retinal damage from laser pulses of one nanosecond to one hundred femtoseconds in the visible and near-infrared wavelength regimes.We have determined the most likely damage mechanism(s) operative in this pulse width regime and discuss implications on laser safety standards.