REVIEW Stereoscopy in Surgical Neuroanatomy: Past, Present, and Future Roberto Rodriguez Rubio, Since the dawn of antiquity, scientists, philosophers, and artists have pondered the nature MD ‡§¶∗ of optical stereopsis—the perception of depth that arises from binocular vision. The Rina Di Bonaventura, MD§∗ early19thcenturysawtheadventofstereoscopes,devicesthatcouldreplicatestere- Ioannis Kournoutas, BS§ opsis by producing a 3D illusion from the super-imposition of 2D photographs. This Downloaded from https://academic.oup.com/ons/article/18/2/105/5520488 by guest on 26 September 2021 phenomenon opened up a plethora of possibilities through its usefulness as an educa- Dania Barakat, BA§ tional tool—particularly in medicine. Before long, photographers, anatomists, and physi- § Vera Vigo, MD cians were collaborating to create some of the first stereoscopic atlases available for the Ivan El-Sayed, MD§¶ teaching of medical students and residents. In fields like neurosurgery—where a compre- Adib A. Abla, MD‡§ hensive visuospatial understanding of neuro-anatomical correlates is crucial—research into stereoscopic modalities are of fundamental importance. Already, medical institutions ‡ Department of Neurological Surgery, all over the world are capitalizing on new and immersive technologies—such as 3D intra- University of California, San Francisco, California; §Skull Base and Cerebrovas- operative recording, and 3D endoscopes—to refine their pedagogical efforts as wellas cular Laboratory, University of California, improve their clinical capacities. The present paper surveys the history of stereoscopy ¶ San Francisco, California; Department of from antiquity to the modern era—with a focus on its role in neurosurgery and medical Otolaryngology - Head and Neck Surgery, University of California, San Francisco, education. Through the tracking of this evolution, we can discuss potential benefits, future California directions, and highlight areas in which further research is needed. By anticipating these factors, we may strive to take full advantage of an emergent field of technology, for our ∗These authors contributed equally to this work. ultimate goal of improving patient care. KEY WORDS: Three-dimensional, History, stereoscope, Neuroanatomy, Education, 3D imaging, 3D videos, Correspondence: Volumetric models, Extended reality, Virtual reality, Holograms Roberto Rodriguez Rubio, MD, Department of Neurosurgery and OHNS, Operative Neurosurgery 18:105–117, 2020 DOI: 10.1093/ons/opz123 Skull Base & Cerebrovascular Laboratory, University of California, San Francisco, 513 Parnassus Ave HSE 817 Box 0112, San Francisco, CA 94143. euroanatomy—the study of the organi- Stereopsis—the perception of depth that Email: [email protected] zation of the central nervous system— results from binocular vision—has long been N is one of the most fascinating and investigated as a feature to be manipulated Received, October 11, 2018. ancient topics within anatomy. Historically, its for educational and functional ends. Research Accepted, December 13, 2018. Published Online, June 19, 2019. teaching in the medical context has been rooted into SS modalities has yielded many notable in cadaveric dissections and dates back to the products that can emphasize the spatial corre- C Congress of Neurological Surgeons ancient Greek physician Herophilos (335-280 lations between neurovascular structures. Some 2019. BC). Through the ages, the primary challenge of of these recent technological advancements in This is an Open Access article distributed neuroanatomy has been in learning the intricate neurosurgery include: 3D visualization systems under the terms of the Creative 3-dimensional topography—an oft difficult task for surgical microscopes, 3D endoscopes, 3D Commons Attribution- given the scarcity of cadaveric specimens and exoscopes, virtual reality (VR) simulators, NonCommercial-NoDerivs licence 1 (http://creativecommons.org/licenses/ the 2D nature of drawings and photographs. surgical robotics, and advanced neuroimaging by-nc-nd/4.0/), which permits In the context of optics, anatomists refer to apparatuses. non-commercial reproduction and 3D images and 3D videos as “stereoscopic” Tracking the history of this transition from distribution of the work, in any medium, (SS)—nomenclature based on the phenomena of 2D representation to 3D imaging allows us to provided the original work is not altered or transformed in any way, and that the stereopsis. speculate on future directions. This paper offers work is properly cited. For commercial a historical narrative on stereoscopy—including re-use, please contact its first applications in neuroanatomy and neuro- [email protected] ABBREVIATIONS: SS, Stereoscopy; VM, Volumetric surgery, with the goal of highlighting its unique models; VR, virtual reality value in medical pedagogy. OPERATIVE NEUROSURGERY VOLUME 18 | NUMBER 2 | FEBRUARY 2020 | 105 RODRIGUEZ RUBIO ET AL THE ORIGINS OF STEREOSCOPY The fundamentals of stereoscopy are based on the fact that humans have a binocular vision—a feature that allows for depth perception. As early as 300 BC, Euclid observed that an image of an object seen by a person’s 2 eyes was dissimilar2—the disparity between the left and right eye allowed for 2 unique viewing angles. Later Ptolemy (AD 127-165), expanded and formalized Euclid’s ideas in his 5-volume work “Optica”.3 Soon after, Galen (ca. AD 129-201) also described this phenomenon—dubbed binocular parallax—in which each eye sees distinct parts of an object which are then perceived as a unified 3D image. Downloaded from https://academic.oup.com/ons/article/18/2/105/5520488 by guest on 26 September 2021 During the medieval dark ages in Europe, Middle-Eastern scholars such as Ibn al-Haytham (965-1040AD) continued to study the physiology of visual perception—his magnum opus, the “Book of Optics” promoted the theory that perception arises from light entering the eye at different angles.4 Centuries later Leonardo da Vinci (1452-1519), noted that “certain portions of distant objects that were hidden from one eye by a near object became visible to the other eye when it was opened”.5 On several occasions Da Vinci expressed his frustration that a 2D painting could never fully recreate the depth experienced when viewing FIGURE 1. A lenticular stereoscope. Public Domain. real objects.6,7 While many more scientists documented this phenomenon of binocular disparity and its role in perception, it was not until the 19th century that the principle of stereoscopy began to flourish. Nevertheless, SS modalities continued to evolve was fully elucidated and techniques to reproduce stereopsis were 8 developed.8,9 as their scientific applications remained useful. In 1832, Sir Charles Wheatstone (1802-1875) demonstrated that it was possible to artificially reproduce 3D-binocular vision FROM THE STEREOSCOPE TO THE by super-imposing slightly different drawings of an object VIEWMASTER: NEUROANATOMICAL through optical means.10,11 He invented the first stereoscope and APPLICATIONS utilized different types of prisms and mirrors to customize the SS effect. In June 1838, his discovery was formally published and Among the earliest users of the newly evolved stereo- presented before the Royal Society of London. The advent of early photography in the scientific realm were medical scholars who photographic techniques led Wheatstone, early in 1839, to reach taught their interns through three-dimensional imaging of human out to Fox Talbot to prepare SS talbotypes of statues, buildings, anatomy. and even portraits.12 Ten years later, British scientist Sir David The first collection of anatomic SS illustrations was prepared by Brewster made SS pictures via the newly minted Daguerreotype Scottish anatomist Daniel John Cunningham (1850-1909). His process, the first commercially successful photographic method, work “Stereoscopic Studies of Anatomy” was published in 1905 and which was invented by Louis-Jacques-Mandé Daguerre. was composed of 5 sections among which 1 cataloged the central In 1844, Brewster went on to invent an improved stereoscope, nervous system (Figure 2). Later, in 1919, after Cunningham’s the “lenticular stereoscope”, which was the first portable, 3D death, the collection was edited by a former collaborator named viewing device (Figure 1). It employed prismatic lenses made David Waterston, who organized a new 10 Volume work with from a double convex lens cut across its diameter—which he 324 black and white SS photographs.15 This collection repre- put in place of the mirrors and prisms employed by Wheat- sents a remarkable set of original SS photographs, each of which stone. With this stereoscope, Brewster was able to view a 3D is mounted on a card stock and designed to be viewed through a image created by the superimposition of 2 individual photographs SS viewer. taken by a camera which was moved sideways, by a distance of A similar collection—but one totally focused on 2.5” between the 2 exposures13—to mimic binocular disparity. SS neuroanatomy—was produced in 1947 by H. S. Rubinstein cameras became commercially available around 1857 and interest and C.L. Davis. Their atlas of neuroanatomy was published by in stereoscopy began to rise exponentially. At one point, enthu- Grune & Stratton, New York,16 and offered 43 plates printed on siasts formally founded a Stereoscopic Society, an organization heavy cardboard and an accompanying descriptive manual. The with the slogan “no home without a stereoscope”.14 Overtime, the plates portrayed the SS photographs