All the under-water and under-ice cosmic neutrino detectors can be described as a grid of optical sensors called optical module, sparse over large volumes of matter and sensitive to the Cherenkov radiation emitted by the charged products of the neutrino interactions. Despite the same scientific objects and global requirements, all the different projects adopted different layout and technical solutions for their optical modules, which are the key sensitive part of the whole detector. Photomultipliers of different characteristics and sizes are housed into transparent glass vessels of different dimensions, and different layout and technical solution are adopted to compose the optical modules. Ice Cube, ANTARES and Baikal GVD projects used a single 10-inch large area photomultiplier housed into a 13-inch or 17-inch diameter transparent glass vessel. The KM3NeT project proposed a novel multi-PMT design, with 31 small area 3-inch photomultipliers integrated into a 17-inch diameter glass housing. Differences are also present on electronics, power supply, magnetic shielding and signals communication. The KM3NeT segmented photocathode layout has several advantages against designs with single large photomultipliers, and indeed this solution is gradually under spread among many of the next generation Cherenkov detectors. Each PMT indeed works independently, offering higher efficiency in photon counting, optical background rejection and directional information just at the level of the single optical module detection, all together with an almost uniform field of view. The proposed poster aims then to give a general overview about layout and components of the main different optical module designs, focusing particularly on the performances of the novel multi-PMT solution of the KM3NeT project.