Optoelectronic moire projector for real-time shape and deformation studies of the tympanic membrane

Abstract

Moire´ topography is a valuable technique for studying the shape and deformation of delicate biological structures such as the tympanic membrane. A projection moire´ method is described that can produce both shape and deformation fringes in real time, at a rate of 25 interferograms per second. The apparatus is based on electronic subtraction of the projected grating line image of the object and a reference grating line image stored in digital memory. The image field and fringe plane distance can be adjusted to the object dimensions. Using a fringe plane distance of 82 mm, a precision of 5 mm over a measuring depth of 0.4 mm is demonstrated by measurements on a spherical calibration object. The application to in vitro shape and deformation measurements of the gerbil tympanic membrane is demonstrated.