Perimeters are commercially available instruments for measuring various attributes of the visual field in a clinical setting. They have several advantages over traditional lab-based systems for conducting vision experiments, including built-in gaze tracking and calibration, polished appearance, and attributes to increase participant comfort.

The Open Perimetry Interface (OPI), a standard set of functions that can be used to control perimeters. Currently the standard is partially implemented in the open-source programming language R on two commercially available instruments: the Octopus 900 (a projection-based bowl perimeter produced by Haag-Streit, Switzerland) and the Heidelberg Edge Perimeter (a CRT-based system produced by Heidelberg Engineering, Germany), allowing these instruments to be used as a platform for psychophysical experimentation.