A camera that directly measures physical parameters.

Abstract

Accurate measurement of physical parameters is essential for the practice of modern medicine and ophthalmology in particular. A measuring device is presented that combines a single lens reflex (SLR) camera body incorporating two aligned in-camera grids with a calibrated macrozoom attachment. The device has multiple applications wherever accurate measurements are required. The ability to measure and record physical parameters in both health and disease is essential to modern medical practice. This is particularly so in ophthalmology. Despite the relative accessibility of external structures, the clinician's measuring equipment often takes the form of a clear plastic ruler with the ever present possibility of inaccuracy from parallax and perspective. Indeed, even in the hands of expert observers, the results from the commercially produced Hertel exophthalmometer are prone to significant variation. Various photographic methods of measurement have been described using a fixed focal length lens system, and recently evaluated. These, however, require processing of the photographs before measurements can be taken. We present a simple, relatively inexpensive multi-purpose device which can measure physical parameters directly and record photographic evidence of these measurements. In essence, the device consists of a single lens reflex (SLR) camera fitted with two carefully aligned grids, linked to a calibrated macrozoom lens.