The<unk>  is an instrument for examining the visual field.<unk> s have been in clinical use since the mid-nineteenth century. Initially, examination of the visual field was concerned only with the outer limits, or 'perimeter' of the visual field, hence the term 'perimetry', which tends to be used inter-changeably with 'campimetry'.
Campimeter
Esthesiometer
Perineometer
Keratometer
Dolorimeter
Focometer
Stadiometer
Lensmeter