Abstract:

Classic otoscopes are modern diagnostic instruments that allow users to examine and evaluate human or animal ears, including their tympanic membranes. In the last years and along with new technologies like the development of the laser after 1960, traditional otoscopes were further improved by the introduction of and combination with other optical systems and technologies. One advance in otoscope technology also involved the introduction/functional integration of optical alignments and system components that were initially used in (surgical) endoscopes, and which gave rise to new devices called “otoendoscopes” or (sometimes) “telescope otoendoscopes” (Olympus America, 2012) – a de- vice classification that fuses and unites classic otoscopes with systematic concepts of endoscopic systems. Those otoscope setups offer distinct advantages compared to tra- ditional otoscopes, like a larger Field of View (FOV) and Depth of Field (DOF), tailored (variable) optical magnifications, refocus abilities for an extended focus/object distance range in front of the otoscope (by simple axial shifts of system components like the ocular), or an additional exit pupil stability (i.e., improved lateral tolerances in case of human eye/head movements). This master’s thesis aims to pick up an older, already drafted HEINE visual otoen- doscope design and carry out a feasibility study regarding the realizability of a hybrid otoendoscope: A device which features not only the “classic” visual system part (to be used by the examiner’s eye) and merges in components from endoscopic system concepts, but additionally contains a second, digital beam path for a simultaneously camera-based examination. Based on the already existing (visual-only) otoendoscope design, such a hybridized system offers further possibilities to create, share and archive image data in parallel to the common, visual in-ear examination and generates additional data for, e.g., digital patient recordings during a regular examination scenario. At the end, the thesis’ development project outlines possible design limitations, conceptual tradeoffs, and provides answers to three hypothetic questions: 1. Is the system design to be realized with a simple (optical) fix-focus design approach? 2. Does the system solution appropriately yield the desired simultaneous and synchro- nized observation of the same in-ear plane by the eye and the camera chip? 3. Are exactly all given/applied (optical) design requirements fulfilled and covered by both beam paths simultaneously? To approach the realization of this new and unique hybrid otoendoscope concept, dif- ferent previously unknown design requirements (prospective benchmarks) for the new prototype’s FOV diameter, its resolution and its DOF capabilities are first derived and set according to analyzed reference data of comparable, already existing commercial oto- and otoendoscope solutions. The thesis project then continues with the modification of HEINE’s existing visual otoendoscope layout and the optics design of the new hybridized otoendoscope system, such that, at the project’s end, the assembled prototype can finally be tested, evaluated and validated via the defined (contrast) evaluation methods and with respect to the settled design specifications. The design requirement determination founds on different image characterization methods (pixel data evaluation and histogram/edge contrast criteria) which are accord- ingly developed and introduced to characterize the commercial reference devices with respect to their imaging performance of defined spatial structures in front of the otoscope tips. The FOV size determination is done via a pixel-based evaluation of the image (area) with reference to the overall image size and a given spatial frequency component on the test chart. The contrast criteria, relevant for the benchmarking of the devices’ resolution and DOF performances, found on the assessment of spatially aligned, rectangular struc- tures on a USAF 1951 resolution test chart whose average pixel (area) gray scale values (histogram contrast criterion) or gray scale line profiles of the edges between two adjacent rectangles (edge contrast criterion) yield the respective contrast characteristics. As for the project results, the eventually optimized and assembled system solution could not be realized via a fix-focus design approach since the performance requirements could, during the optical system simulation, not be fulfilled for the given otoendoscope design concept. Instead, a suitable system solution was found via a fixed intermediate image (plane) position buried inside the system, and whose information content changes, depending on the axial shifts (axial positioning) of the otoendoscope’s relay group, thus forwarding the addressed object plane information to the static intermediate image plane. This intermediate image plane is optically accessed by both beam paths, such that a synchronized observation of the same object plane is guaranteed and the hybrid otoendoscope’s functionality is realized. However, the characterization results show that, although the “beam path synchronization” (device hybridization) was achieved, the prototype’s performance only satisfies one of three optic design requirements (the FOV requirement), while the required resolution performances and DOF depths could not entirely be fulfilled. Those device benchmarks result, additionally supported by simulated opto-mechanical tolerances of the designed camera objective, primarily from given (project-related) design and manufacturing constraints, such that, e.g., for the digital beam path, more than 80 % of the 100 simulated, randomly manufactured and assembled optical alignments (Monte Carlo systems) did not yield sufficient resolution and DOF outcomes. Nonetheless, the basic device functionality proved to be feasible/realizable, and was, in principle, implemented, such that – for the project outlook – the hybrid otoendoscope prototype concept needs to be refined via the adjustment of the underlying (optics) design parameters and requirements. Additionally, prospective researchers will also have to address, contact and question the actual users directly to clarify further, central improvement topics which primarily involve the device’s usability, the refined and user- oriented parameter weighting of the device’s (optical) design concept, and the device’s (optical) calibration process (which, so far and as hypothetically proposed, could not sufficiently be achieved with reference to the eye’s retinal image only).