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The Vitreous: Making the Invisible Visibleby 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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that developed connections with other spaces only after a degenerative process of the vitreous.8 To emphasize this, they changed the term premacular bursa to pos-terior precortical vitreous pocket (PPVP). With the de-velopment of vitrectomy and use of intraocular stains, these structures were later visualized using triamcino-lone intraoperatively.9

THE VITREOUS IN THE OCT ERA

With the advent of optical coherence tomog-raphy (OCT), our understanding of in vivo ocular

anatomy, and pertinently, vitreous anatomy, has expanded dramatically. Many have utilized the en-hanced imaging capabilities of OCT to better under-stand the vitreous.10,11 In 2014, we developed an im-aging protocol that allowed us to enlarge the size of the area scanned to 18 × 18 mm using swept-source OCT (SS-OCT).12 This approach made it possible to demonstrate that the premacular bursa is limited in-feriorly, but contrary to what had been previously reported, continues superiorly beyond the reach of our instruments (Figures 1C and 1D).13 This scan-

Figure 1. The top left image depicts schematically how the premacular bursa and prepapil-lary gap fuse at a variable dis-tance from the optic nerve in the majority of adult eyes and is lim-ited inferiorly but extends superi-orly. These spaces can be readily seen on spectral-domain optical coherence tomography (OCT) and swept-source OCT. The hori-zontal B-scan below the optic nerve (A) shows how the area of Martegiani (the posterior portion of the prepapillary gap overlying the optic nerve head) is sepa-rated from the bursa (asterisk) by formed vitreous – the “septum interpapillomaculare” of Worst. The horizontal B-scan above the optic nerve (B) shows that the two spaces have fused, but a ridge persists as a legacy of the septum. The vertical B-scan in through the more central (C) and temporal macula (D) shows that the bursa (asterisk) is confined to the posterior pole inferiorly, but extends beyond the scan range superiorly. Adapted from: Engel-bert M. A new understanding of vitreous structure. Review of Ophthalmology. 2016;01:60-64.

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ning technique also provided visualization of the area of Martegiani separated from the bursa by the septum interpapillomaculare as described by Worst (Figure 1A).13 This separation disappears superiorly at a variable distance from the optic nerve, there-by creating a connection between these two spaces (Figure 1B).13 This differs from the small connection proposed by Kishi et al., who used SS-OCT to de-scribe a connection between the PPVP and Cloquet´s canal.10 It also differs from the supposed connection between the premacular bursa and the retrociliary circle of cisterns proposed by Worst.14 Instead, we pictured these spaces like a mitten, with the thumb part over the area of Martegiani, the finger and palm

part over the macula, and the wrist and arm mak-ing their way towards the front of the eye, possibly terminating behind the lens in the space of Ergge-let (Figure 1).14 The overall shape of the premacular bursa appears to be uniform early in life but may vary in size, as seen in a father and son with Stick-ler’s disease.15 They presented with a “giant premac-ular bursa,” which may represent an optically empty vitreous in the setting of attached cortical vitreous.15

Our recent work also supported some of Eisner’s work on prevascular fissures.16 In our study of nor-mal volunteers, we detected thin hyporeflective spaces in the vitreous overlying first- and second-order blood vessels in young individuals without

Figure 2. Swept-source optical coherence tomography (SS-OCT) images of three different subjects showing prevascular fissures (PVF) and their location above retinal blood vessels (black arrowheads). Infrared images in A, C, and E with arrows indicating scan position cor-responding to vertical SS-OCT scans in B, D, and F. The black arrow points to a blood vessel with no PVF above it. Adapted from: Pang CE, Schaal KB, Engelbert M. Association of prevascular vitreous fissures and cisterns with vitreous degeneration as assessed by swept source optical coherence tomography. Retina. 2015;35:1875-1882.

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Figure 3. Two subjects showing the relationship between premacular bursa (asterisks) and cisterns (white triangles). Infrared images in A and C with arrows indicating scan position corresponding to vertical swept-source optical coherence tomography scans in B and D. A and B show a teardrop configured cistern with no visible connection to the premacular bursa in the right eye of a 36-year-old man with an axial length (AL) of 24.1 mm. C and D show a bowl-configured cistern with visible connection to the premacular bursa in the left eye of a 51-year-old man with an AL of 24.2 mm. Adapted from: Pang CE, Schaal KB, Engelbert M. Association of prevascular vitreous fissures and cisterns with vitreous degeneration as assessed by swept source optical coherence tomography. Retina. 2015;35:1875-1882.

vitreous degeneration, corroborating the presence of the spaces Eisner had first described decades ago (Figure 2).6,7,16 With time, the vitreous is known to degenerate and these fissures appear to transform into bigger spaces, which likely correspond to the cisterns Worst described (Figure 3).16 Fissure planes in the more central vitreous appear also related to this degenerative process.13 A recently described aspect is the lamellar arrangement of fibers in the vitreous cortex.17 A novel model of fibrillar vitreous architecture characterized by a pattern of eyewall-parallel vitreous fibers with a tangential course toward the equator forms the vitreous cortex with some perpendicular fibers delimiting spaces deep inside the vitreous (premacular bursa, prepapillary gap, and prevascular fissures and cisterns).17 This lamellar pattern is compatible with the idea that with time and as degenerative changes ensue, the lamellae begin to separate, potentially resulting in vitreoschisis.

CLINICAL AND SURGICAL CORRELATIONS

Knowledge of the normal vitreous anatomy and its characteristic aging changes is helpful in the clinical

and surgical setting.18 For instance, it is well known that abnormal hyaloid adherence and tangential trac-tion are implicated in the pathogenesis of vitreomac-ular traction (VMT) and macular hole (MH) forma-tion. However, the status of the vitreous may also play an important role in those disorders.19 Although it might seem intuitive that eyes with advanced vitre-ous degeneration would have higher rates of macular holes or VMT, in fact, the opposite may be true.19 In a comparative study of eyes with VMT and MH versus control eyes, the former demonstrated significantly earlier stages of vitreous degeneration as compared to their matched controls, even when the latter were on average, younger. This may be because a degenerated vitreous creates a compartmentalization that buffers the inertia counterforces to the vitreoretinal interface (Figure 4), whereas a well-formed structure more ef-fectively transmits any force applied to it.19 Going forward, this may allow for better prognostication for our patients regarding the likelihood of developing a vitreoretinal interface disease. It may also facilitate treatment, or one might postulate that a treatment that advances vitreous degeneration may concurrent-ly reduce the risk of VMT or MH.

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A better in vivo understanding of the vitreous can also be helpful in the postoperative course, as was true in this report in which SS-OCT was used to identify residual cortical vitreous in a patient with persistent floaters after surgery that were otherwise invisible on clinical examination (Figure 5).20

The vitreous also plays an outsized role in the development of other intraocular diseases, includ-ing and especially in diabetes mellitus. Although known to impact the metabolic regulation through-out the body, in the vitreous, diabetic changes can lead to early liquefaction and cross-linking of the collagen network in a process known as diabetic vit-

Figure 4. Eyes on the vitreomacular trac-tion (VMT)-macular hole (MH) spectrum were found to be more likely to have a relatively intact vitreous gel (A), whereas eyes with an uneventful contralateral posterior vitreous detachment and no VMT in the study eye were significantly more likely to show more extensive vit-reous degeneration with fissure planes (P = .048) (B, C). Diagrammatic horizon-tal section of an eye with formed vitreous, with saccadic forces being transmitted from more central formed vitreous onto the vitreoretinal interface without mitiga-tion (D), whereas compartmentalization in an eye with more advanced vitreous degeneration and fissure planes buffers these forces (E). Adapted from: Ghadiali Q, Zahid S, Dolz-Marco R, Tan A, Engel-bert M. An Assessment of Vitreous De-generation in Eyes with Vitreomacular Traction and Macular Holes. J Ophthal-mol. 2017;2017:6834692.

Figure 5. Widefield image (left) of a 28-year-old myope who complained of a crescentic opacity in his superotemporal peripheral field after undergoing vitrectomy for symptomatic vitreous opacities. Swept-source optical coherence tomography (1 and 2) demonstrated that a posterior vitreous detachment had been induced (red arrowhead), but that there was a residual posterior hyaloidal skirt with scalloped edges, presumably from cutter bites (green arrowhead). Further propagation of the vitreous separation and close shaving of the gel relieved this patient of his symptoms. Adapted from: Chen KC, Jung JJ, Engelbert M. Swept source optical coherence tomography of the posterior vitreous after pars plana vitrectomy. Graefes Arch Clin Exp Ophthalmol. 2015;253(11):2041-2043.

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reopathy.21,22 In a 2017 paper exploring the relation-ship between retinal neovascularization in patients with diabetic retinopathy and the posterior vitreous, nearly 80% of these membranes had grown along the outer surface of the posterior hyaloid face.23 Even the classic “wolf’s jaw” configuration of neovascu-larization, which has been shown to track along the venous arcades, proliferates along the posterior hya-loid.23 However, in the setting of a largely attached vitreous cortex, the neovascularization can pene-

trate the posterior hyaloid and grow along the walls of prevascular fissures or cisterns, giving rise to flat, broad and tightly adherent plaques that can be chal-lenging to tackle surgically. Given this information, a clear understanding of the relationship between diabetic neovascularization and the vitreous can not only aid in understanding this disease but also in surgical planning for these patients (Figure 6).23 Finally, the idea suggested by Kishi that the boat-shaped preretinal hemorrhages are confined to the

Figure 6. An appreciation of the complex relationship of diabetic neovascularization and the posterior hyaloid and the vitreous spaces is helpful in the surgical management of proliferative diabetics. The near infrared image (A) shows an active neovascular complex growing along a partially separated hyaloid. Schematic representation of a situation that can be approached readily with a cutter in B. C shows early neovascularization into a cistern in the setting of an attached posterior hyaloid. This is probably the precursor to flat, tightly adherent plaques that are not just tethered by a few pegs, and – if extensive – have to be delaminated bimanually. Adapted from: Vaz-Pereira S, Dansingani KK, Chen KC, Cooney MJ, Klancnik JM Jr, Engelbert M. Tomographic relationships between retinal neovascularization and the posterior vitreous in proliferative diabetic retinopathy. Retina. 2017;37(7):1287-1296.

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premacular bursa and that their morphology is ac-counted by the shape of the latter24,25 was dismissed; OCT showed that the premacular bursal wall is per-meable to erythrocyte passage, and an intrabursal bleed is followed by rapid infiltration of the adjacent vitreous gel by erythrocytes, giving rise to a hemor-rhage with more indistinct margins (Figure 7).26

CONCLUSION

The vitreous is a complex structure that involved in diverse pathologic processes. As our multi-modal imaging capabilities have expanded, so too has our

understanding of in vivo anatomy and with that, the opportunity to better understand vitreoretinal pa-thology. Further research will continue to grow this knowledge base and provide an even more complete understanding of the vitreous and its impact.

REFERENCES

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2. Fine BS, Tousimis AJ. The structure of the vitreous body and the suspensory ligaments of the lens. Arch Ophthalmol. 1961;65(1):95-

Figure 7. Intrabursal hemorrhage due to Valsalva retinopathy. Ophthalmoscopy revealed a boat-shaped hemorrhage with indistinct mar-gins adjacent to the inferior vascular arcade and a second hemorrhage inferior to the optic disk (A). There was no leakage identified on fluorescein angiography, but blockage over the vein the hemorrhage likely originated from B (red arrowhead). The vitreous was imaged using swept source optical coherence tomography, and the areas imaged with line scans are illustrated in the reflectance image (C). Note that erythrocytes are predominantly localized within the vitreous gel between the premacular bursa (stars) and the cortical vitreous. The bursal cavity itself is relatively devoid of erythrocytes; however, accumulation of erythrocytes within the vitreous adjacent to the bursa creates the impression that the bursal wall is lined with blood. Also note that the vitreous is attached at the macula, and the subhyaloid space is optically clear without any evidence of hemorrhage. Adapted from: Balaratnasingam C, Vaz-Pereira S, Engelbert M. Intrabursal and Subhyaloid Hemorrhages in Valsalva Retinopathy. Retina. 2017;37(1):e1-e3.

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3. Worst JGF. The bursa intravitrealis premacularis: New develop-ments in ophthalmology. In: Deutman AF, ed. New Developments in Ophthalmology Nijmegen 16–18 October 1975. Springer, Dordrecht; 1976:275-279. https://doi.org/10.1007/978-94-010-1569-1_31

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8. Kishi S, Shimizu K. Posterior precortical vitreous pocket. Arch Ophthalmol. 1990;108(7):979-982. https://doi.org/10.1001/ar-chopht.1990.01070090081044 PMID:2369358

9. Fine HF, Spaide RF. Visualization of the posterior precorti-cal vitreous pocket in vivo with triamcinolone. Arch Ophthalmol. 2006;124(11):1663. https://doi.org/10.1001/archopht.124.11.1663 PMID:17102022

10. Itakura H, Kishi S, Li D, Akiyama H. Observation of posterior pre-cortical vitreous pocket using swept-source optical coherence tomog-raphy. Invest Ophthalmol Vis Sci. 2013;54(5):3102-3107. https://doi.org/10.1167/iovs.13-11769 PMID:23599325

11. Spaide RF. Visualization of the posterior vitreous with dynamic fo-cusing and windowed averaging swept source optical coherence to-mography. Am J Ophthalmol. 2014;158(6):1267-1274. https://doi.org/10.1016/j.ajo.2014.08.035 PMID:25174895

12. Pang CE, Freund KB, Engelbert M. Enhanced vitreous imaging technique with spectral-domain optical coherence tomography for evaluation of posterior vitreous detachment. JAMA Ophthalmol. 2014;132(9):1148-1150. https://doi.org/10.1001/jamaophthal-mol.2014.1037 PMID:25010436

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14. Engelbert M. A new understanding of vitreous structure. Rev Oph-thalmol. 2016;01:60-64.

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16. Pang CE, Schaal KB, Engelbert M. Association of prevascular vitreous fissures and cisterns with vitreous degeneration as assessed by swept source optical coherence tomography. Retina. 2015;35(9):1875-1882. https://doi.org/10.1097/IAE.0000000000000540 PMID:25874366

17. Gal-Or O, Ghadiali Q, Dolz-Marco R, Engelbert M. In vivo imaging of the fibrillar architecture of the posterior vitreous and its relationship to the premacular bursa, Cloquet’s canal, prevascular vitreous fissures, and cisterns. Graefes Arch Clin Exp Ophthalmol. 2019;257(4):709-714. https://doi.org/10.1007/s00417-018-04221-x PMID:30617583

18. Kishi S. Diagnostic pearls in the management of vitreomacu-lar disorders. Semin Ophthalmol. 1998;13(1):2-9. https://doi.org/10.3109/08820539809066077 PMID:9567007

19. Ghadiali Q, Zahid S, Dolz-Marco R, Tan A, Engelbert M. An Assess-ment of Vitreous Degeneration in Eyes with Vitreomacular Traction and Macular Holes. J Ophthalmol. 2017;2017:6834692. https://doi.org/10.1155/2017/6834692 PMID:28133544

20. Chen KC, Jung JJ, Engelbert M. Swept source optical coherence to-mography of the posterior vitreous after pars plana vitrectomy. Graefes Arch Clin Exp Ophthalmol. 2015;253(11):2041-2043. https://doi.org/10.1007/s00417-015-3018-y PMID:25904299

21. Sebag J. Diabetic vitreopathy. Ophthalmology. 1996;103(2):205-206. https://doi.org/10.1016/S0161-6420(96)30716-1 PMID:8594502

22. Stitt AW, Moore JE, Sharkey JA, et al. Advanced glycation end products in vitreous: structural and functional implications for dia-betic vitreopathy. Invest Ophthalmol Vis Sci. 1998;39(13):2517-2523. PMID:9856760

23. Vaz-Pereira S, Dansingani KK, Chen KC, Cooney MJ, Klancnik JM Jr, Engelbert M. Tomographic relationships between retinal neovas-cularization and the posterior vitreous in proliferative diabetic reti-nopathy. Retina. 2017;37(7):1287-1296. https://doi.org/10.1097/IAE.0000000000001336 PMID:27749694

24. Kishi S, Shimizu K. Clinical manifestations of posterior precorti-cal vitreous pocket in proliferative diabetic retinopathy. Ophthal-mology. 1993;100(2):225-229. https://doi.org/10.1016/S0161-6420(93)31666-0 PMID:8437831

25. Kishi S. Vitreous anatomy and the vitreomacular correlation. Jpn J Ophthalmol. 2016;60(4):239-273. https://doi.org/10.1007/s10384-016-0447-z PMID:27165709

26. Balaratnasingam C, Vaz-Pereira S, Engelbert M. Intrabursal and Subhyaloid Hemorrhages in Valsalva Retinopathy. Retina. 2017;37(1):e1-e3. https://doi.org/10.1097/IAE.0000000000001149 PMID:28005722

Gerardo Ledesma-Gil, MD, can be reached at Vitreous Retina Macula Consultants of New York, 950 3rd Ave., 3rd floor, New York, NY 10022; email: gerardo.ledesma.md@gmail.com.

Pedro Fernández-Avellaneda, MD, can be reached at Vitreous Retina Macula Consultants of New York, 950 3rd Ave., 3rd floor, New York, NY 10022; email: pedro.fdezavellaneda@gmail.com.

Talia R. Kaden, MD, can be reached at Department of Ophthalmology, Manhattan Eye, Ear and Throat Hospital, New York, New York; email: talia.kaden@gmail.com.

Howard F. Fine, MD, MHSc, can be reached at can be reached at Rutgers Robert Wood Johnson Medical School; New Jersey Retina, 10 Plum Street, Suite 600, New Brunswick, NJ 08901; email: hfine@njretina.com.

Michael Engelbert MD, PhD, can be reached at Vitreous Retina Macula Consultants of New York, 950 3rd Ave., 3rd floor, New York, NY 10022; email: michael.engelbert@gmail.com.

Disclosures: Dr. Engelbert is a consultant for Genentech, Bayer, Allergan, and Alimera Sciences. Dr. Fine is a consultant and/or speaker for Alimera, Allergan, Genentech, Regeneron, and Spark Therapeutics and has equity/patent interests in Auris Surgical Robotics. The remaining authors report no relevant financial disclosures.