Cirrus clouds consist almost exclusively of nonspherical ice particles. This complex nature of cirrus clouds gives rise to many controversial issues in the remote sensing of these clouds from satellite-based sensors. One issue recently receiving substantial attention is whether pristine ice particles with high-order regularity (e.g., hexagonal ice columns and ice bullet rosettes) or irregular ice particles (e.g., aggregates, ice crystals with rough surfaces or internal inclusions of air bubbles) predominate in cirrus clouds. In this study, we elucidate the relevance of this issue to the retrieval of thin cirrus cloud optical thickness from the 1.38-micron band of MODIS (Moderate-resolution Imaging Spectroradiometer). We will also discuss the implications of our findings for climate studies, specifically, the shortwave radiative forcing of cirrus clouds.