To see the invisible: The quest of imaging vitreous

Abstract

Imaging vitreous is an attempt to view what is by design invisible (Figure II.F-1). The inability to adequately image vitreous hinders a more complete understanding of its normal structure and function, its role in ocular health, and how things change in aging and disease. As described by Duke-Elder [1], the theories of human anatomy that were prevalent during the mid-eighteenth century proposed that the vitreous is composed of “loose and delicate filaments surrounded by fluid,” a description that is remarkably close to present-day concepts. During the eighteenth and nineteenth centuries, there were no less than four very different theories of vitreous structure: in 1741 Demours proposed the alveolar theory; in 1780 Zinn offered the concentric, lamellar configuration theory; in 1845 Hannover suggested the radial sector theory; and in 1848 Sir William Bowman proposed the fibrillar theory, later championed by Retzius and Szent-Gyorgi. Unfortunately, as pointed out by Redslob [2], the techniques employed in all these studies were flawed by artifacts that biased the results of the investigations, since they employed acidic tissue fixatives that precipitated what we recognize today as the glycosaminoglycans, hyaluronan. Thus, the development of slit-lamp biomicroscopy by Gullstrand in 1912 held great promise, as it was anticipated that this technique could enable imaging of vitreous structure without the introduction of fixation artifacts. Yet, as described by Redslob [2], a varied set of descriptions resulted over the years, ranging from a fibrous structure to sheets, “chain-linked fences,” and various other interpretations. This problem has even persisted in more recent investigations. Eisner [3] described “membranelles”; Worst [4] “cisterns”; Sebag and Balazs [5] “fibers”; and Kishi and Shimizu [6] “pockets” in the vitreous [7].