Vitreous body

Vitreous humour

Schematic diagram of the human eye.
Details
Identifiers
Latin humor vitreus
TA A15.2.06.014
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

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 humor 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.

Significance

Clinical

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. 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.

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.

Forensic

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.[2][3][4]

Properties

Biochemical

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 humor 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.[5] 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.[6]

Inorganic ion content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Sodium 146.7 mmol/L [7] Yes
Potassium 5.73 mmol/L [7] Yes
Chloride 121.6 mmol/L [7] Yes
Calcium 1.13 mmol/L [7] Yes
Magnesium 0.9 mmol/L [7] Yes
Phosphate 0.1 to 3.3 mEq/dm3 [8] No
Bicarbonate 1.2 to 3.0 g/kg water [8] No
Inorganic coenzyme content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Copper 0.52 µmol/L [7] Yes
Selenium 0.104 µmol/L [7] Yes
Iron 3.11 µmol/L [7] Yes
Manganese 110.7 nmol/L [9] Yes
Organic content of vitreous
Solute Mean concentration Units Reference Data from living humans?
Glucose 2.97 mmol/L [7] Yes
Lactate 3.97 mmol/L [7] Yes
Lipids 2 μg/mL [8] No
Total protein content 280-1360 μg/cm3 [8] No
Hyaluronan 42-400 μg/cm3 [8] No
Versican 60 μg/cm3 [8] No
Collagen 300 μg/mL [10] No
Albumin 293 ± 18 μg/cm3 [8] No
Immunoglobulin (IgG) 33.5 ± 3 μg/cm3 [8] No
α1-Antitrypsin 141 ± 2.9 μg/cm3 [8] No
α1-Acid glycoprotein 4 ± 0.7 μg/cm3 [8] No
Osmolality 289.5 mOsm/kg [7] Yes
Beta-hydroxybutyrate 0.094 mmol/L [7] Yes
Ferritin 19.52 µg/L [7] Yes
Transferrin 0.088 g/L [7] Yes
Urea 24-172 mg/dL water [8] No
Creatinine 0.3-3.0 mg/dL water [8] No
Citrate 1.9 mg/dL water [8] No
Pyruvic acid 7.3 mg/dL water [8] No
Ascorbic acid 36 mg/100g [8] No

Physical

Physical properties of vitreous
Property Value Units Reference Data from living humans?
Volume 3.9 mL [8] No
Weight 3.9 g [8] No
Water content 99 to 99.7 % [8] No
pH 7.4 to 7.52 [8] No
Osmolality 289.5 mOsm/kg [7] Yes
Osmotic pressure (Freezing-point depression) -0.554 to -0.518 °C [8] No
Density 1.0053 to 1.0089 g/cm3 [8] No
Intrinsic viscosity 3-5 × 103 cm3/g [8] No
Dynamic viscosity 1.6 cP [8] No
Refractive index 1.3345 to 1.337 [8] No
Gel and liquid volume of human vitreous as a function of age
Age (years) Gel volume (cm3) Liquid volume (cm3) Reference
Birth 1.6 0 [8]
5 3.3 0 [8]
10 3.5 0.7 [8]
20 3.9 0.9 [8]
30 3.9 0.9 [8]
40 3.9 0.9 [8]
50 3.5 1.3 [8]
60 3.2 1.6 [8]
70 2.8 2.0 [8]
80 2.5 2.3 [8]
90 2.2 2.6 [8]
Transmittance of radiation through human vitreous
Wavelength (nm) Transmittance (total, %) Reference Data from living humans?
300 0 [11] Yes
325 76 [11] Yes
350 82 [11] Yes
400 90 [11] Yes
500 97 [11] Yes
600 98 [11] Yes
700 98 [11] Yes
Rheological characteristics of vitreous at various locations
Parameter Anterior vitreous Central vitreous Posterior vitreous Units Reference
Residual viscosity 1.4 2.2 4.9 ηm (Pa s) [8]
Internal viscosity 0.3 0.35 0.5 ηk (Pa s) [8]
Relaxation time 0.38 0.30 1.61 τm (s) [8]
Retardation time 0.27 0.41 0.46 τk (s) [8]
Elastic compliance (instantaneous) 0.1 0.3 0.3 Jm (m−2 N−1) [8]
Elastic modulus (internal) 2.5 1.3 1.2 Gk (Pa) [8]

Anatomical

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.[12][13][14]

Surface features:

Internal structures of the vitreous

Named tracts

Aging

Additional images

See also

References

  1. ↑ "Associated Structures - Vitreous". Teaching.pharmacy.umn.edu. Retrieved 2012-12-07.
  2. ↑ 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: 158–166. doi:10.1016/j.forsciint.2015.07.020.
  3. ↑ 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.
  4. ↑ "Postmortem Vitreous Analyses: Overview, Vitreous Procurement and Pretreatment, Performable Postmortem Vitreous Analyses" – via eMedicine.
  5. ↑ "eye, human."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009
  6. ↑ The Vitreous Humor Archived April 26, 2007, at the Wayback Machine.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 "Biochemical analysis of the living human vitreous". ResearchGate. Retrieved 2016-03-09.
  8. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Murphy, William; Black, Jonathan; Hastings, Garth (11 June 2016). "Handbook of Biomaterial Properties". Springer – via Google Books.
  9. ↑ "Manganese in the Human Vitreous". ResearchGate. 1 March 2016.
  10. ↑ Velpandian, Thirumurthy (29 February 2016). "Pharmacology of Ocular Therapeutics". Springer – via Google Books.
  11. 1 2 3 4 5 6 7 Boettner, Edward A.; Wolter, J. Reimer (1 December 1962). "Transmission of the Ocular Media". Invest. Ophthalmol. Vis. Sci. 1 (6): 776–783 – via iovs.arvojournals.org.
  12. ↑ http://image.slidesharecdn.com/anatomyoflens-151014144942-lva1-app6892/95/anatomy-of-lens-6-638.jpg?cb=1444834244
  13. ↑ http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v7/0010/025f.jpg
  14. ↑ http://www.oculist.net/downaton502/prof/ebook/duanes/graphics/figures/v6/0510/001f.jpg

External links

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