Mobile computer devices and systems for refraction determination of an eye, for example for objective refraction determination and/or subjective refraction determination, are provided. Here, a display of the mobile computer device can be driven to display an image for refraction determination. The mobile computer device includes a display, a processor and a non-transitory computer-readable medium having a program code stored therein. The program code is configured to cause the processor to drive only the display to display an image thereon for determining refraction of the eye.