OSLI Retina

June 2020

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312 Ophthalmic Surgery, Lasers & Imaging Retina | Healio.com/OSLIRetina Practical Retina Incorporating current trials and technology into clinical practice The Vitreous: Making the Invisible Visible by Gerardo Ledesma-Gil, MD; Pedro Fernández-Avellaneda, MD; Talia R. Kaden, MD; and Michael Engelbert MD, PhD The introduction of the ophthalmo- scope by Hermann von Helmholtz in 1851, and later modifications to produce the binoc- ular indirect oph- thalmoscope by Charles Schepens in 1945, allowed visualization of the retina, optic nerve, and vitreous cav- ity. These develop- ments were turning points in ophthal- mology because they allowed physi- cians to visualize structures that were previously imperceptible. The anatomy of the vitreous is vi- tally important in normal and diseased states, such as vitreomacular traction, macular holes, and diabetic tractional retinal detachments. Yet the vitreous anatomy typically remains obscured because it is largely transparent to vis- ible light. In this installment of Practical Ret- ina, Gerardo Ledesma-Gil, MD; Pedro Fernández-Avellaneda, MD; Talia R. Kaden, MD; and Michael Engelbert MD, PhD, all from New York City, dis- cuss visualization of the human vitre- ous in vivo. Optical coherence tomog- raphy, particularly swept-source, has been one of the major imaging advanc- es to drape the proverbial sheet over the ghost. Their original research and comprehensive overview of recent advances in understanding the vitre- ous anatomy are sure to enlighten the retina community. By volume, the vitre- ous is the largest compo- nent of the eye and yet it is often overlooked by both comprehensive ophthal- mologists and retina spe- cialists alike. In part, this is because it is difficult to see, both on clinical exam and on multimodal imag- ing. However, the latter is beginning to change, and in the process, much is being learned about this enigmatic structure. The vitreous gel is a virtually acellular, highly hydrated (> 98% water) extracellular matrix. Its structure is maintained by a network of unbranched collagen fibrils comprised of collagen types II, V, IX, and XI. The glycosaminoglycan (GAG) hyaluronan is a major component that fills the spaces between these collagen fibrils. 1 Although essential to the optical properties of the eye, the fact that it is an almost optically clear medium composed mainly of water makes it difficult to accurately describe its anatomical state. Initially, the only source of information available was through in vivo biomicroscopic observations with an ophthalmoscope or a slit-lamp, providing a good but somewhat superficial insight as to its structure. 2 Ex vivo histologic studies were unreliable due to numerous post-fixation artifacts caused by the high water content of the samples. 2 This changed in 1976 when Jan Worst injected ink into the vitreous of postmortem eyes and identified a system of liquid spaces within the vitreous gel consisting of what he called the premacular bursa and cisterns surrounding the latter. 3,4 Georg Eisner continued to expand our understanding when he used a modified slit-lamp camera to analyze postmortem eyes and not only confirmed Worst's findings, 5 but also discovered areas of low- er optical density in the vitreous cortex above the vessels, which he named "lücken," ("gaps"), or prevascular fissures. 6,7 In 1990, Ki- shi and Shimizu stained the vitreous with fluorescein in cadaveric eye specimens. 8 They discovered that the premacular bursa was separated from the retina posteriorly by a thin layer of cortical tis- sue. 8 They also defined the bursa as a boat-shaped, confined space Gerardo Ledesma- Gil Talia R. Kaden Michael Engelbert Pedro Fernández- Avellaneda doi: 10.3928/23258160-20200603-01 Howard F. Fine Practical Retina Co-Editor

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