Portable lensmeters and portable lensmeter modules are disclosed. In one embodiment, a portable lensmeter module comprises a housing having an aperture formed therethrough and having a first slot formed therein for receiving and reversibly coupling to a lens; a light source disposed within the housing; and a microlens array disposed within the housing. The lens and the microlens array define an optical channel from the light source to the aperture when the lens is coupled to the housing; and a light detector of a mobile device is positioned adjacent to the aperture and at a focal point of the microlens array when the lensmeter module is mechanically coupled to the mobile device.