To support refinement of the ANSI Maximum Permissible Exposure safety limits, a series of experiments were conducted in vivo on Dutch Belted rabbit corneas to determine corneal minimum visible lesion thresholds for $2.0\mathrm{\mu }\mathrm{m}$ continuous-wave laser irradiation. Single pulse radiant exposures were made at specified pulse durations of 0.1, 0.25, 0.5, 1.0, 2.0, and $4.0\mathrm{s}$ for spot $1∕e^2$ diameters of $1.17\mathrm{mm}$ and $4.02\mathrm{mm}$ . Threshold lesions were defined as the presence of a superficial surface whitening one hour after irradiation. Temperature measurements indicated that threshold peak temperatures were dependent on spot size and exposure duration. The exposure duration dependence of threshold average radiant exposure was described by an empirical power law equation: threshold radiant $\mathrm{exposure}[\mathrm{J}∕{\mathrm{cm}}^2]=a\times \mathrm{exposure}$ $\mathrm{duration}[\mathrm{s}{]}^b$ .