Vitreous body

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Vitreous humour
Schematic diagram of the human eye en.svg
Schematic diagram of the human eye.
Details
Identifiers
Latin humor vitreus
TA A15.2.06.014
A15.2.06.008
FMA 67388
Anatomical terminology

The vitreous body is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates. It is often referred to as the vitreous humour or simply "the vitreous".

Structure[edit]

The vitreous humour is a transparent, colorless, gelatinous mass that fills the space in the eye between the lens and the retina. It is present at birth.[1] Produced by cells in the non-pigmented portion of the ciliary body, the vitreous humour is derived from embryonic mesenchyme cells, which degenerate after birth.

The vitreous humour is in contact with the retina and helps to keep it in place by pressing it against the choroid. It does not adhere to the retina, except at the optic nerve disc and the ora serrata (where the retina ends anteriorly), at the Wieger-band, the dorsal side of the lens. It is not connected at the macula, the area of the retina which provides finer detail and central vision.

Aquaporin-4 in Müller cell in rats, transports water to the vitreous body.[2][3]

Anatomical features[edit]

The vitreous has many anatomical landmarks, including the hyaloid membrane, Berger's space, space of Erggelet, Wieger's ligament, Cloquet's canal and the space of Martegiani.[4][5][6]

Surface features:

Internal structures of the vitreous

  • The vitreous body at birth is homogenous with a finely striated pattern.
  • With early aging the vitreous develops narrow transvitreal "channels".
  • The cortex is denser than the centre with development.
  • From adolescence, vitreous tracts form from anterior to posterior.
  • These vitreous tracts are fine sheet-like condensations of vitreous.

Named tracts

  • Retrolental tract: Extends posteriorly from the hyaloideocapsular ligament into central vitreous
  • Coronary tract: External to the retrolental tract, and excluding posteriorly from a circular zone overlying the posterior 1/3rd of the ciliary processes
  • Median tract: Extends back from a circular zone external to the coronary tract, at the anterior margin of the vitreous base
  • Preretinal tract: Extends back from the ora serrata and vitreous base

Development[edit]

The nature and composition of the vitreous humour changes over the course of life. At birth, the fluid is homogenous and finely striated (except Cloquet's canal).[citation needed] In adolescence, the vitreous cortex becomes more dense and vitreous tracts develop; and in adulthood, the tracts become better defined and sinuous. Central vitreous liquefies, fibrillar degeneration occurs, and the tracts break up (syneresis).[citation needed]

Coarse strands develop with ageing. The gel volume decreases with age, and the liquid volume increases.[7] Cortex may disappear at sites, leading to liquid vitreous extruding into the potential space between vitreous cortex and retina (vitreous detachment)

Posterior vitreous detachment: Once liquid vitreous enters the sub-hyaloid space between vitreous cortex and retina, it strips the vitreous cortex off the retina with each eye movement.

Clinical significance[edit]

Injury[edit]

Unlike the fluid in the frontal parts of the eye (aqueous humour) which is continuously replenished, the gel in the vitreous chamber is stagnant. Therefore, if blood, cells or other byproducts of inflammation get into the vitreous, they will remain there unless removed surgically[8][9]. These are known as floaters. If the vitreous pulls away from the retina, it is known as a vitreous detachment. As the human body ages, the vitreous often liquefies and may collapse. This is more likely to occur, and occurs much earlier, in eyes that are nearsighted (myopia). It can also occur after injuries to the eye or inflammation in the eye (uveitis).

The collagen fibres of the vitreous are held apart by electrical charges. With aging, these charges tend to reduce, and the fibres may clump together. Similarly, the gel may liquefy, a condition known as synaeresis, allowing cells and other organic clusters to float freely within the vitreous humour. These allow floaters which are perceived in the visual field as spots or fibrous strands. Floaters are generally harmless, but the sudden onset of recurring floaters may signify a posterior vitreous detachment (PVD) or other diseases of the eye.

Postmortem and forensic[edit]

After death, the vitreous resists putrifaction longer than other body fluids. The vitreous potassium concentration rises so predictably within the hours, days and weeks after death, that vitreous potassium levels are frequently used to estimate the time-of-death (Post-mortem interval) of a corpse.[10][11][12]

The metabolic exchange and equilibration between systemic circulation and vitreous humour is so slow that vitreous humour is sometimes the fluid of choice for postmortem analysis of glucose levels or substances which would be more rapidly diffused, degraded, excreted or metabolized from the general circulation.

Properties[edit]

Biochemical[edit]

Its composition is similar to that of the cornea, but the vitreous contains very few cells. It is composed mostly of phagocytes, which remove unwanted cellular debris in the visual field, and hyalocytes, which turn over the hyaluronan.

The vitreous humour contains no blood vessels, and 98–99% of its volume is water (as opposed to only 75% in the cornea). In addition to water, the vitreous consists of salts, sugars, vitrosin (a type of collagen), a network of collagen type II fibrils with glycosaminoglycan, hyaluronan, opticin, and a wide array of proteins. Despite having little solid matter, the fluid is substantial enough to fill the eye and give it its spherical shape. The lens, on the other hand, is tightly packed with cells.[13] The vitreous humour has a viscosity two to four times that of water, giving it a gelatinous consistency. It has a refractive index of 1.336.[14]

Inorganic ion content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Sodium 146.7 mmol/L [15] Yes
Potassium 5.73 mmol/L [15] Yes
Chloride 121.6 mmol/L [15] Yes
Calcium 1.13 mmol/L [15] Yes
Magnesium 0.9 mmol/L [15] Yes
Phosphate 0.1 to 3.3 mEq/dm3 [7] No
Bicarbonate 1.2 to 3.0 g/kg water [7] No
Inorganic coenzyme content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Copper 0.52 µmol/L [15] Yes
Selenium 0.104 µmol/L [15] Yes
Iron 3.11 µmol/L [15] Yes
Manganese 110.7 nmol/L [16] Yes
Organic content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Glucose 2.97 mmol/L [15] Yes
Lactate 3.97 mmol/L [15] Yes
Lipids 2 μg/mL [7] No
Total protein content 280–1360 μg/cm3 [7] No
Hyaluronan 42–400 μg/cm3 [7] No
Versican 60 μg/cm3 [7] No
Collagen 300 μg/mL [17] No
Albumin 293 ± 18 μg/cm3 [7] No
Immunoglobulin (IgG) 33.5 ± 3 μg/cm3 [7] No
α1-Antitrypsin 141 ± 2.9 μg/cm3 [7] No
α1-Acid glycoprotein 4 ± 0.7 μg/cm3 [7] No
Osmolality 289.5 mOsm/kg [15] Yes
Beta-hydroxybutyrate 0.094 mmol/L [15] Yes
Ferritin 19.52 µg/L [15] Yes
Transferrin 0.088 g/L [15] Yes
Urea 24–172 mg/dL water [7] No
Creatinine 0.3–3.0 mg/dL water [7] No
Citrate 1.9 mg/dL water [7] No
Pyruvic acid 7.3 mg/dL water [7] No
Ascorbic acid 36 mg/100g [7] No

Physical[edit]

Physical properties of vitreous
Property Value Units Reference Data from living humans?
Volume 3.9 mL [7] No
Weight 3.9 g [7] No
Water content 99 to 99.7  % [7] No
pH 7.4 to 7.52 [7] No
Osmolality 289.5 mOsm/kg [15] Yes
Osmotic pressure (Freezing-point depression) -0.554 to -0.518 °C [7] No
Density 1.0053 to 1.0089 g/cm3 [7] No
Intrinsic viscosity 3–5 × 103 cm3/g [7] No
Dynamic viscosity 1.6 cP [7] No
Refractive index 1.3345 to 1.337 [7] No

Additional images[edit]

See also[edit]

References[edit]

  1. ^ "Associated Structures – Vitreous". Teaching.pharmacy.umn.edu. Retrieved 2012-12-07. 
  2. ^ Sim?, Rafael; Villarroel, Marta; Corraliza, L?dia; Hern?ndez, Cristina; Garcia-Ram?rez, Marta (2010). "The Retinal Pigment Epithelium: Something More than a Constituent of the Blood-Retinal Barrier?Implications for the Pathogenesis of Diabetic Retinopathy". Journal of Biomedicine and Biotechnology. 2010: 1–15. doi:10.1155/2010/190724. 
  3. ^ Nagelhus, EA; Veruki, ML; Torp, R; Haug, FM; Laake, JH; Nielsen, S; Agre, P; Ottersen, OP (1 April 1998). "Aquaporin-4 water channel protein in the rat retina and optic nerve: polarized expression in Müller cells and fibrous astrocytes.". The Journal of neuroscience : the official journal of the Society for Neuroscience. 18 (7): 2506–19. PMID 9502811. These data suggest that Muller cells play a prominent role in the water handling in the retina and that they direct osmotically driven water flux to the vitreous body and vessels rather than to the subretinal space 
  4. ^ http://image.slidesharecdn.com/anatomyoflens-151014144942-lva1-app6892/95/anatomy-of-lens-6-638.jpg?cb=1444834244
  5. ^ http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v7/0010/025f.jpg
  6. ^ http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v6/0510/001f.jpg
  7. ^ a b c d e f g h i j k l m n o p q r s t u v w x y Murphy, William; Black, Jonathan; Hastings, Garth (11 June 2016). "Handbook of Biomaterial Properties". Springer – via Google Books. 
  8. ^ www.arkeo.com, produced by Arkeo, Inc.,. "Associated Structures - Vitreous". teaching.pharmacy.umn.edu. Retrieved 9 June 2017. The vitreous does not undergo a regular formation and drainage process like the aqueous humor. Instead, it stays permanently in the vitreous body of the eye 
  9. ^ "Oxford Eye Hospital Vitrectomy Information for patients" (PDF). p. 3, part 2. The jelly does not naturally replace itself and is substituted with one of the following 
  10. ^ Zilg, B.; Bernard, S.; Alkass, K.; Berg, S.; Druid, H. (17 July 2015). "A new model for the estimation of time of death from vitreous potassium levels corrected for age and temperature". 254: 158–66. doi:10.1016/j.forsciint.2015.07.020. 
  11. ^ Kokavec, Jan; Min, San H.; Tan, Mei H.; Gilhotra, Jagjit S.; Newland, Henry S.; Durkin, Shane R.; Casson, Robert J. (19 March 2016). "Antemortem vitreous potassium may strengthen postmortem interval estimates". 263. doi:10.1016/j.forsciint.2016.03.027. 
  12. ^ "Postmortem Vitreous Analyses: Overview, Vitreous Procurement and Pretreatment, Performable Postmortem Vitreous Analyses" – via eMedicine. 
  13. ^ "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
  14. ^ The Vitreous Humor Archived April 26, 2007, at the Wayback Machine.
  15. ^ a b c d e f g h i j k l m n o "Biochemical analysis of the living human vitreous". ResearchGate. Retrieved 2016-03-09. 
  16. ^ "Manganese in the Human Vitreous". ResearchGate. 1 March 2016. 
  17. ^ Velpandian, Thirumurthy (29 February 2016). "Pharmacology of Ocular Therapeutics". Springer – via Google Books. 

External links[edit]