Anatomy & Physiology of the Vitreous & the Vitreoretinal Interface

The vitreous gel is a transparent extracellular matrix that fills the cavity behind the lens of the eye. It occupies an average volume of 4.4 ml in adulthood. It is surrounded by and attached to the retina and lens of the eye.[1]It is a virtually acellular, highly hydrated extracellular gel matrix, composed of approximately 99% water.[15]The transparent nature of the vitreous makes it challenging to study its structure and anatomy.

The gel structure is maintained by a dilute network of thin, unbranched collagen fibrils that are mixed (heterotopic) in composition, comprising collagen types II, V/XI and IX in a molar ratio of 75:10:15, respectively. Collagen type V/XI forms the core of the fibrils, with type II surrounding the core and type IX on the outside of the fibril. The spaces between these collagen fibrils are mostly filled by glycosaminoglycans (GAGs), mainly hyaluronan.[15]Opticin has been found to coat the collagen fibers and, by binding to different GAGs, may play a role in maintaining the gel structure of the vitreous and also in adhesion at the vitreoretinal interface.[1517]Chondroitin sulfate, another GAG linked to type IX collagen, was found to play a role in bridging adjacent collagen fibrils and at the same time spacing them apart to minimize light scattering and maintain vitreous transparency.[18]The vitreoretinal interface is an adhesive sheet that facilitates the connection of the posterior vitreous cortex of the vitreous body to the internal limiting membrane of the retina.[6]The vitreoretinal interface consists of matrix proteins including laminin, fibronectin and collagen IV,[18,19]and it is thought that these may act as an extracellular matrix 'glue'.[6]It is not completely understood how the vitreous and retina interact. The vitreous is known to be most firmly attached at places where the internal limiting membrane is thinnest, that is, the vitreous base, optic disc and macula, and over retinal blood vessels.[1]At the base area, the vitreous and the retina are connected by vitreous collagen fibers passing though the internal limiting membrane and intertwining with retinal collagen.[20]The collagen fibrils of the posterior vitreous cortex are indirectly attached to the internal limiting membrane, and hence to the retina via laminin and fibronectin,[21]as shown in Figure 1. The attachment between the vitreous and the macula is called the vitreomacular interface.

(Enlarge Image)Figure 2.

Protein bonds in the vitreomacular interface.

Starting in the fourth decade of life, the vitreous body witnesses a significant decrease in gel volume with a concomitant increase in the liquid volume. Derangement of the normal association between hyaluronan and collagen results in the simultaneous aggregation of collagen fibrils into bundles of parallel fibrils seen as large fibers and the formation of large pockets of liquid vitreous recognized clinically as 'lacunae'. By 8090 years of age, more than half of the vitreous is liquid.[22]With aging, weakening of the adhesion between the posterior vitreous cortex and the internal limiting membrane occurs, probably due to biochemical alterations in the vitreoretinal interface.[23,24]One component of the extracellular matrix of the vitreoretinal interface, galactose (1,3)-N-acetylglucosamine, is no longer present in adults.[25]Several studies demonstrated that an intact vitreoretinal interface has been found in patients less than 60 years of age, despite extensive vitreous liquefaction.[1]After the age of 60 years, weakening of the posterior vitreous cortex/internal limiting membrane adhesion at the posterior pole occurs, allowing liquid vitreous to enter the retrocortical space. Volume displacement from the central vitreous to the preretinal space causes the observed collapse of the vitreous body,[6]usually leading to posterior vitreous detachment.

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Papers of special note have been highlighted as:

of interest

of considerable interest

Expert Review of OphthalmologyVitreomacular Interface Diseases

Pathophysiology, Diagnosis and Future Treatment Options

Aniz Girach, Steve Pakola

DisclosuresExpert Rev Ophthalmol.2012;7(4):311-323.

http://www.medscape.com/viewarticle/772188_3 PrintAnatomi & Fisiologi Vitreous & yang vitreoretinal Antarmuka

Vitreous gel adalah matriks ekstraseluler transparan yang mengisi rongga di belakang lensa mata. Ini menempati volume rata-rata dari 4,4 ml di masa dewasa. Hal ini dikelilingi oleh dan melekat pada retina dan lensa mata. [1] Ini adalah hampir acellular, sangat terhidrasi matriks ekstraseluler gel, terdiri dari sekitar 99% air. [15] transparan sifat vitreous membuatnya menantang untuk mempelajari struktur dan anatomi.

Struktur gel dikelola oleh jaringan encer tipis, fibril kolagen bercabang yang dicampur (heterotopic) dalam komposisi, terdiri dari kolagen tipe II, V / XI dan IX dalam rasio molar 75:10:15, masing-masing. Kolagen tipe V / XI membentuk inti dari fibril, dengan tipe II sekitar inti dan tipe IX di luar urat saraf. Ruang antara fibril kolagen sebagian besar diisi oleh glycosaminoglycans (GAG), terutama Hyaluronan. [15] Opticin telah ditemukan untuk melapisi serat kolagen dan, dengan mengikat GAG yang berbeda, mungkin memainkan peran dalam mempertahankan struktur gel vitreous dan juga dalam adhesi pada antarmuka vitreoretinal. [15-17] Chondroitin sulfat, GAG lain terkait dengan mengetik kolagen IX, ditemukan untuk memainkan peran dalam menjembatani fibril kolagen yang berdekatan dan pada jarak waktu yang sama mereka terpisah untuk meminimalkan hamburan cahaya dan memelihara transparansi vitreous. [18] antarmuka vitreoretinal adalah lembar perekat yang memfasilitasi sambungan dari vitreous korteks posterior vitreous body pada membran membatasi internal retina. [6] Antarmuka vitreoretinal terdiri dari protein matriks termasuk laminin, fibronektin dan kolagen IV, [18,19] dan diperkirakan bahwa dapat bertindak sebagai 'lem' matriks ekstraselular. [6]

Hal ini tidak sepenuhnya dipahami bagaimana vitreous dan retina berinteraksi. Vitreous diketahui paling melekat erat di tempat di mana membran batas yang tertipis, yaitu, basis vitreous, disk optik dan makula, dan lebih dari pembuluh darah retina. [1] Di daerah basis, vitreous dan retina dihubungkan oleh serat kolagen vitreous lewat meskipun internal membatasi membran dan terjalinnya dengan kolagen retina. [20] fibril kolagen dari vitreous korteks posterior secara tidak langsung melekat pada membran batas, dan karenanya ke retina melalui laminin dan fibronektin, [21 ] seperti yang ditunjukkan pada Gambar 1. Lampiran antara vitreous dan makula disebut antarmuka vitreomacular.

(Perbesar Gambar)

Gambar 2.

Obligasi protein dalam antarmuka vitreomacular.

Dimulai pada dekade keempat kehidupan, saksi vitreous body penurunan yang signifikan dalam volume gel dengan seiring bertambahnya volume cairan. Kekacauan asosiasi normal antara Hyaluronan dan hasil kolagen dalam agregasi simultan fibril kolagen ke dalam bundel fibril paralel dilihat sebagai serat besar dan pembentukan kantong besar vitreous cair diakui secara klinis sebagai 'kekosongan'. Dengan 80-90 tahun, lebih dari setengah dari vitreous cair. [22]

Dengan penuaan, melemahnya adhesi antara korteks posterior vitreous dan membran batas terjadi, mungkin karena perubahan biokimia dalam antarmuka vitreoretinal [23,24] Salah satu komponen dari matriks ekstraseluler dari antarmuka vitreoretinal, galaktosa (1,. 3)-N-asetilglukosamin, tidak lagi hadir pada orang dewasa. [25] Beberapa penelitian menunjukkan bahwa antarmuka vitreoretinal utuh telah ditemukan pada pasien kurang dari 60 tahun, meskipun pencairan vitreous yang luas. [1] Setelah usia 60 tahun, melemahnya vitreous posterior korteks / internal yang membatasi adhesi membran pada kutub posterior terjadi, sehingga vitreous cairan masuk ke ruang retrocortical. Volume perpindahan dari vitreous pusat ke ruang preretinal menyebabkan runtuhnya diamati dari tubuh vitreous, [6] biasanya mengarah ke posterior vitreous detachment.