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When Sight Penetrates the Body: The Use and Promotion of Stereoscopic Radiography in Britain, 1896–1918
Published in Andrew Graciano, Visualizing the Body in Art, Anatomy, and Medicine since 1800, 2019
However, such an argument was not expressed by Davidson. The latter never gave much importance to the conservation of the natural conditions of binocular vision. In fact, he systematically neglected the relationship between accommodation and convergence in his methodological guidance. As a stereoscope was not always available, he even suggested a technique to produce a stereoscopic effect without any instrument, by slightly squinting so that each optical axis would fall on the proper picture.54 A correct effect requires, as C. Fred Bailey later related, that “the accommodation must not be allowed to alter with convergence or the combined picture will be out of focus.”55 No such explanation is found in Davidson’s work. While the surgeon claimed that the practice of stereoscopic vision by squinting was “not difficult to acquire,” most radiographers disagreed.56 They complained about headaches even if not realizing their distress was the result of altering their physiological condition.57 Because of the difficulty and the lack of precision of his method, it seems that Davidson was certainly not looking for an exact reconstitution of the process of binocular vision. Neither was he concerned with creating a precise and accurate visual model. For Davidson, then, the visual quality potentially produced by the Wheatstone stereoscope when used correctly was beside the point.
Toward Clinically Viable Ultrasound-Augmented Laparoscopic Visualization
Published in Terry M. Peters, Cristian A. Linte, Ziv Yaniv, Jacqueline Williams, Mixed and Augmented Reality in Medicine, 2018
The system described by Kang et al. includes a stereoscopic vision system (VSII, Visionsense, Philadelphia, PA, USA), an LUS scanner (BK Flex Focus 700, Analogic, Peabody, MA, USA) employing an intraoperative 9-mm rigid transducer, an optical tracking system (Polaris, Northern Digital, Waterloo, ON, Canada), and a desktop computer running image fusion software. The vision system features a stereoscopic, three-dimensional (3D), 5-mm, 0° laparoscope with an integrated light source and fixed focal length, both of which simplify its use in the OR. The 3D laparoscope has been reported to improve depth perception and achieve good clinical outcomes.
Challenging patients and circumstances
Published in James Barrett, Transsexual and Other Disorders of Gender Identity, 2017
More subtly, mild visual defects such as an amblyopic dysconjugate gaze may prove unexpectedly handicapping. An uncertain fixity of gaze causes others to stare harder than would otherwise be the case. This increased scrutiny can be unwelcome and unhelpful. Some would argue that surgery to produce a conjugate gaze would be helpful in these circumstances, even if it were too late to allow stereoscopic sight or any other objective improvement in visual function.
A Review to Populate A Proposed Cost-Effectiveness Analysis of Glaucoma Screening in Sub-Saharan Africa
Published in Ophthalmic Epidemiology, 2022
Olusola Olawoye, Augusto Azuara-Blanco, Ving Fai Chan, Prabhath Piyasena, Grainne E. Crealey, Ciaran O’Neill, Nathan Congdon
Ophthalmoscopy (Direct): Direct ophthalmoscope is often used to examine the optic nerve head with or without dilation of the pupil. An advantage of the direct ophthalmoscope is its portability and use of batteries instead of electrical current, access to which may be problematic in remote areas. The main disadvantage, however, is its inability to give a stereoscopic view of the nerve. Harper et al.68 reported a sensitivity of 81% (95% CI 69–89%) and a specificity of 90% (95% CI 84–95%) with the use of the instrument, when compared to a gold standard of stereophotography in the evaluation of the narrowest rim width for glaucoma screening.68 Cook et al.69 reported that the use of the direct ophthalmoscope using a cut-off of 0.7 for the vertical cup to disc ratio, in addition to the testing for afferent pupil defect, could give an accuracy of up to 90% for the case detection of glaucoma.
Alfred Wilhelm Volkmann on stereoscopic vision
Published in Strabismus, 2022
It is in Part 3 of the translation that Volkmann cites Wheatstone’s16 second, and much neglected, memoir in binocular vision. In it Wheatstone described and illustrated an adjustable mirror stereoscope, a prism stereoscope, and a pseudoscope for reversing disparities. The main purpose of these was to extend the range of conditions under which the two eyes could be stimulated. Wheatstone used the stereoscope with adjustable arms to vary retinal size, convergence, accommodation, and disparity. He found that “The perceived magnitude of an object, therefore, diminishes as the inclination of the axes becomes greater, while the distance remains the same; and it increases, when the inclination of the axes remains the same, while the distance diminishes. When both of these conditions vary inversely, as they do in ordinary vision when the distance of an object changes, the perceived magnitude remains the same”16(p3). On the basis of these experiments, as well as his own Volkmann appreciated that stereoscopic depth involves psychological as well as physiological processes: “The psychological influences are very important in the theoretical consideration because they make any explanation of the discussed fusion process through innate relations impossible”9(p189).
The vision of Helmholtz
Published in Journal of the History of the Neurosciences, 2021
Presenting different stimuli to each eye was transformed by the invention of the stereoscope. It could be argued that the stereoscope heralded the revolution in vision (see Wade 2004, 2016), and the instrument was embraced by Helmholtz. He initiated research on binocular vision in the 1850s and invented the telestereoscope in 1857, although his experiments on binocular vision were undertaken in the early 1860s while he was in Heidelberg. The stereoscope was important to Helmholtz, both for the experimental world it exposed and also for his inferential theory of vision. In prosecuting his experimental enquiries, Helmholtz developed the reflecting stereoscope so that disparities could be enhanced. This was achieved by extending the separations between the mirrors, and he called the instrument a telestereoscope; his diagram of it is shown, together with his portrait, in Figure 7.