Tunica Vasculosa Lentis

Importance of the vitreous body for the eye: The vitreous body stabilizes the globe although the eye can remain intact without the vitreous body (see vitrectomy). It also prevents retinal detachment.

Embryology: The development of the vitreous body can be divided into three phases:

❖ First phase (first month of pregnancy; fetus measures 5-13 mm cranium to coccyx): The primary vitreous forms during this period. This phase is characterized by the entry of mesenchyme into the optic cup through the embryonic choroidal fissure. The main function of the primary vitreous is to supply the developing lens with nourishment. In keeping with this function, it consists mainly of a vascular plexus, the anterior and posterior tunica vasculosa lentis, that covers the anterior and posterior surfaces of the lens. This vascular plexus is supplied by the hyaloid artery and its branches (Fig. 11.1). This vascular system and the primary vitreous regress as the posterior lens capsule develops at the end of the second month of pregnancy.

❖ Second phase (second month of pregnancy; fetus measures 14-70 mm cranium to coccyx): The secondary vitreous forms during this period. This avascular vitreous body consisting of fine undulating collagen fibers develops from what later becomes the retina. In normal development it expands to compress the central primary vitreous into a residual central canal (hyaloid canal or Cloquet's canal).

❖ Third phase (third month of pregnancy; fetus measures 71-110 mm cranium to coccyx): The tertiary vitreous develops from existing structures in the secondary vitreous. The secondary vitreous remains. The zonule fibers that form the suspensory ligament of the lens develop during this period.

Composition of the vitreous body: The gelatinous vitreous body consists of 98% water and 2% collagen and hyaluronic acid. It fills the vitreous chamber, which accounts for approximately two-thirds of the total volume of the eye.

280 11 Vitreous Body Transitory embryonic vascular supply.

Iridohyaloid vessels

280 11 Vitreous Body Transitory embryonic vascular supply.

Iridohyaloid vessels

Iridohyaloid Vessels

Anterior tunica vasculosa lentis and pupillary membrane

Posterior tunica vasculosa lentis

Trunk of the hyaloid artery and envelope of glial tissue

Long posterior ciliary arteries

Fig. 11.1 The anterior tunica vasculosa lentis (dark red) forms anastomoses with the posterior tunica vasculosa lentis (light red) through the iridohyaloid vessels.

Lens

Anterior tunica vasculosa lentis and pupillary membrane

Posterior tunica vasculosa lentis

Trunk of the hyaloid artery and envelope of glial tissue

Long posterior ciliary arteries

Fig. 11.1 The anterior tunica vasculosa lentis (dark red) forms anastomoses with the posterior tunica vasculosa lentis (light red) through the iridohyaloid vessels.

Stabilization and confines of the vitreous body: With their high negative electrostatic potential, the hyaluronic acid molecules fill the three-dimensional collagen fiber network and provide mechanical stability. Condensation of peripheral collagen fibrils creates a boundary membrane (hyaloid membrane), which is not a basement membrane. It is attached to adjacent structures at the following locations (Fig. 11.2):

❖ At the ligament of Wieger along the posterior capsule of the lens.

❖ At the vitreous base at the ora serrata.

❖ At the funnel of Martegiani (approximately 10 ^m wide) surrounding the periphery of the optic disk.

The connections between the vitreous body and retina are generally loose although there may be firm focal adhesions. These firmer focal attachments cause problems during vitreous detachment because they do not permit the vitreous body to become completely detached. The focal adhesions between the vitreous body and retina produce focal traction forces that act on the retina and can cause retinal tears and detachment.

11.2 Examination Methods 281 — Attachments of the vitreous body and adjacent spaces. -

Wieger's band (attachment to the posterior lens capsule)

Vitreous base

(attachment to the ora serrata)

11.2 Examination Methods 281 — Attachments of the vitreous body and adjacent spaces. -

Wieger's band (attachment to the posterior lens capsule)

Vitreous base

(attachment to the ora serrata)

Martegiani's funnel (attachment at the optic disc)

Canal Cloquet

Hyaloid canal

Fig. 11.2 Attachments of the vitreous body are identified by thick red lines and listed on the left. Spaces adjacent to the vitreous body are shown in green and listed on the right.

Garnier's space

Zonular spaces (Petit's canals)

Berger's space

Hyaloid canal

Martegiani's funnel (attachment at the optic disc)

Fig. 11.2 Attachments of the vitreous body are identified by thick red lines and listed on the left. Spaces adjacent to the vitreous body are shown in green and listed on the right.

Neurovascular supply: The vitreous body contains neither blood vessels nor nerves. As a result, pathogens can multiply undisturbed for a relatively long time before the onset of an immune response from adjacent structures.

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Responses

  • Muhammed
    What are the functions of tunica vasculosa lentis?
    4 years ago
  • philip
    What is a vitrous body in electrostatics?
    4 years ago

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