A comparison of the physical optics code and GOIE method to solve the problem of light scattering by hexagonal ice crystals has been presented. It was found that in the case of diffraction on a hole in the perpendicular screen, both methods give the same diffraction scattering cross section for the diffraction angles up to 60 degrees. The polarization elements of the Mueller matrix in this case differ significantly even for the angles of 15-30 degrees. It is also shown that in the case of diffraction on the tilted screen, the difference between these methods may be significant. The comparison of the results with the exact solution obtained by FDTD has confirmed that the difference between these methods is not significant for the case of diffraction on the perpendicular screen, but it is slightly preferable to use the GOIE for the calculations. The good agreement with the exact solution confirms the possibility of using the method of physical optics to solve the problem of light scattering by particles with characteristic size greater than 10 microns.