Anatomy of the vitreous body

Basic science in ophthalmology

1. Anatomy of the vitreous body Presenter Dr.Desta Genete (OR1) Moderator Dr.Dereje (associate professor of ophthalmology, VRS)

2. O utline Introduction Development Anatomy 2

3. I ntroduction The word “vitreous” is derived from a Latin word “ vitrum ” which means glass It's Clear, transparent, gel-like liquid fills the vitreous cavity of the eye vitreous is a dilute solution of salts , soluble proteins, and hyaluronic acid contained within a meshwork collagen. Spherical in shape, volume 4ml and weight 4gm 3

4. Embryology of vitreous

5. Embryology Primary (primitive) vitreous Formed at 4th-5th weeks of gestation, the space between the lens vesicle and the inner layer of the optic cup 6

6. primary vitreous consists Fibrils -ectodermal origin Mesenchymal cells--mostly mesodermal in origin some are derived from neural crest cells Vascular channels of the hyaloid system--mesodermal origin

7. At fifth week of gestation, the primitive dorsal ophthalmic artery gives off the hyaloid artery The hyaloid vasculature reaches its greatest development at about 9 weeks

8. E mbryology cont’d Secondary (definitive) vitreous occurs during the 7th to 8th weeks, after closure of the optic fissure Consists of : A finer, more compact fibrillar network of monocytes The primitive hyalocytes - originate from the vascular primary vitreous (mesenchyme) Collagen fibrils - are produced by the hyalocytes and result in expansion of the secondary vitreous volume Small amount of hyaluronic acid 9

9. In the fifth month , hyaloid atrophy= cloquet canal forms Persistence of the primary vitreous and failure of the posterior tunica vasculosa lentis to regress results in persistent hyperplastic primary vitreous (PHPV) 10 E mbryology cont’d

10. Tertiary vitreous Between 3 rd and 4 th months of gestation, collagen fibrils of the secondary vitreous condense The condensation of fibrils extends to the lens equator and constitutes the tertiary vitreous. The zonular apparatus of the lens ultimately develops anterior to these collagen fibrils At the 6th and 7th months of GA the vitreous regresses to its base on the pars plana and to its attachment to the lens which is called the capsulohyaloid ligamet 11 E mbryology cont’d

11. Cloquet’s canal Represents remnants of hyaloid artery Arises from the optic disc over space of Martegiani Ends in space of Ergglet S shaped course with the downward dip in its central portion Anteriorly is 1-2mm wide, at pattelar fossa is 4-5mm 12

12. Cloquet’s canal cont’d No collagen in its lumen Wall is formed by vitreous condensation rather than true membrane Anterior remnant - Mittendorf dot , a small opacity in the post capsule of lens slightly nasal to the post pole of lens Posterior remnant on the optic disc - Bergmeister's papilla 13

13. P ostnatal development The axial length of vitreous of newborn eye ~ 10.5 mm in M and~ 10.2 mm in F Axial length increase rapidly during the first 5-7 months 13 years~ 16.1 mm in M and ~ 15.6 mm in F In the absence of refractive changes, the mean adult vitreous is 16.5 mm at 18 years of age 14

14. Gross Anatomy Composed 2 main portions: The central, or medullary vitreous The cortical vitreous- outer portion The cortical vitreous further divided Anterior vitreous cortex Posterior vitreous cortex 15

15. Cortical Vitreous The peripheral ‘ shell ’ of vitreous Only 2% of total Vitreous volume Consists of more condensed collagen fibers, cells, proteins & mucopolysccharides Metabolic center of Vitreous , b/c It contains cells; Hyalocyte , Fibrocytes 16

16. Anterior Vitreous Cortex Also called Anterior Hyaloid Face A nterior to the vitreous base Begins 1.5mm anterior to Ora Serrata Collagen fibrils densely packed and parallel to surface of cortex 17

17. Anterior Vitreous Cortex cont’d Smooth surface/membrane like appearance due to lamellar distribution of cortical fibers and associated highly polymerized mucoproteins Form posterior limits of posterior chamber, serves as Communication port b/n Vitreous cavity and Aqueous humor It extends medially to contact lens posterior to lens equator The anterior hyaloid membrane anterior bounding surface ,has retrolental indentation patellar fossa ,anterior depression of vitreous behind lens 18

18. Anterior Vitreous Cortex cont’d HyaloideoCapsular or Weiger Ligament, Annular region of attachment b/n Vitreous and Posterior lens width 1-2 mm and diameter 8-9 mm firmly attached in younger patients after intraocular inflammation Erggelet's or Berger's space, center of hyaloideocapsular ligament 19

19. Vitreous tracts Are fine sheet-like condensation of vitreous tissue radiates in to vitreous space from ciliary body and anterior retina. Give rise to “onion skin” arrangement of adult vitreous Retrolental tract ( tractus retrolentalis ) Inner most vitreous tract From wegier ligament to in front of optic disc It forms a reflecting membrane aka membrane plicata of vogt Coronary tract( tractus coronaries) From coronary ligament to inner vitreous around retrolental Not optically distinct 20

20. lll , Median tract ( tractus medianus ) From median ligament extends backward as faint veil around tractus coronaries into the central vitreous. l v, Preretinal tract( tractus preretinalis ) Outermost vitreous tract From ora serata extends backward around median tract Its more comparatively more reflecting membrane . 21

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22. Also called Posterior Hyaloid Posterior from the vitreous base No vitreous cortex over the optic disc- prepapillary hole 23 Posterior Vitreous Cortex

23. Is 100 to 110 μm thick and consists of densely packed type II collagen fibrils and other extracellular matrix components arranged tangentially to retina It's thin over Macula due to rarefaction of collagen fibrils Boarders with ILM of retina w/c is basement membrane of muller cells 24 Posterior Vitreous Cortex…..cont’d

24. Vitreoretinal interface The basal lamina post to the ora is the basement membrane of retinal muller cells, the ILM of the retina Its anterior surface is smooth while its posterior is irregular No direct connections b/n posterior vitreous cortex and retina posterior vitreous cortex , adherent to ILM of retina 25

25. Vitreoretinal interface cont’d Exact nature of adhesion unknown, but probably results from Action of extracellular matrix molecules found at this interface Type IV collagen fibronectin, laminin type I collagen 26

26. ILM The ILM has three layers Lamina rara interna Lamina densa Lamina rara externa- contagious with the vitreous cortex Thickness 50nm at vitreous base 300nm at equator 1900nm posteriorly. In fovea thins to 10-20nm Cortical collagen fibers insert directly into the ILM which are firm in areas of thinnest ILM (fovea & basal region ) 27

27. ILM cont’d ILM thin over blood vessels , Vitreous strands inserted through pores on ILM It extend through ILM to branch and surround vessels VitreoRetinoVascular Bands These explains strong adhesion b/n vitreous and retinal blood vessels provide shock-absorbing function, damping arterial pulsations during cardiac cycle pathologically , It associated with vitreous traction on retinal blood vessels – vit hemorrhage 28

28. ILM cont’d At the ciliary body the basal lamina is a meshwork of lamina densa with insertion of collagen fibrils The only region not adjacent to the ILM is the annulus of the ant vitreous cortex which is exposed to the zonnules & aqueous. This allows various substances (RBC,HA,GF) to exit vitreous 29

29. Attachments of the vitreous Firm attachments Vitreous base- strongest Posterior lens capsule … hyaloidocapsular ligament of wiegner Margins of optic nerve head At macula Around blood vessels variable and weakest 30

30. Vitreous Base Three-Dimensional zone, centered on ora serrata Extends from ora serrata Anteriorly 1.5 mm Posteriorly Nasally 3.0 mm Temporally 2.0 mm The functional base extends several mm into vitreous body in this region 31

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32. Hyaloido capsular ligament ( retrolental ligament) Is another strong adhesion of vitreous and posterior capsule of the lens. Circular adhesion 8-9mm in diameter The circle of adhesion between vitreous and posteriour lens capsule is often termed as Eggers Line Strength of adhesion decreases with age

33. At macula Vitreous is attached in annular fashion with a diameter of 3-4mm Also attaches along side the larger retinal vessels

34. Medullary vitreous Most of Vitreous body Cell free mixture of HA & collagens Gel or liquid depending on age, refraction or conditions of the eye Is enclosed by the vitreous cortex 35

35. References Duanes clinical ophtalmology 2012 clinical anatomy and physiology of visual system Remington’s 3rd edition ADELER’S physiology of the eye 11 th edition Online sources 3/29/2018 36

36. Thank you