Vitreous Body – Structure, Function and Disorders
The vitreous body is a clear, gel-like substance that fills the interior of the eye between the lens and the retina. It helps maintain the shape of the eyeball and allows light to pass through.
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The vitreous body is a clear, gel-like substance that fills the interior of the eye between the lens and the retina. It helps maintain the shape of the eyeball and allows light to pass through.
What is the Vitreous Body?
The vitreous body (Latin: Corpus vitreum), also known as the vitreous humor, is a transparent, jelly-like substance that occupies the largest part of the interior of the eye. It is located between the crystalline lens and the retina, accounting for approximately 80% of the total volume of the eyeball. Its crystal-clear composition allows light to travel unobstructed from the lens to the retina.
Structure and Composition
The vitreous body consists of approximately 98–99% water. The remaining components include:
- Collagen fibers (primarily type II), forming a three-dimensional network
- Hyaluronic acid, which gives the vitreous its gel-like consistency
- Electrolytes, proteins, and other macromolecules in trace amounts
The unique combination of collagen fibers and hyaluronic acid gives the vitreous body its viscoelastic properties – meaning it behaves both as a liquid and as a solid under different conditions.
Functions of the Vitreous Body
- Optical function: The transparent vitreous allows light to pass through undisturbed to reach the retina.
- Mechanical support: It maintains the retina in its proper position and preserves the spherical shape of the eyeball.
- Shock absorption: The vitreous protects delicate ocular structures such as the lens and the retina from mechanical trauma.
- Metabolic reservoir: It serves as a depot for nutrients and metabolic waste products of the inner eye structures.
Common Conditions Affecting the Vitreous Body
Vitreous Floaters (Mouches Volantes)
As the eye ages, the gel-like structure of the vitreous undergoes changes. Collagen fibers can clump together and cast shadows on the retina, which are perceived as floaters – small dark spots, threads, or cobweb-like shapes drifting across the visual field. Floaters are generally harmless but can be bothersome.
Posterior Vitreous Detachment
Over time, the vitreous loses volume and pulls away from the retina in a process called posterior vitreous detachment (PVD). This commonly occurs after the age of 50 and is often accompanied by an increase in floaters and flashes of light (photopsia). While PVD is usually benign, it can occasionally cause a retinal tear.
Vitreous Hemorrhage
A vitreous hemorrhage occurs when blood vessels rupture and blood leaks into the vitreous cavity. Common causes include diabetic retinopathy, trauma, retinal tears, or other vascular disorders. Affected individuals may experience sudden vision loss or a reddish haze in their visual field.
Vitreous Traction and Retinal Detachment
When the vitreous exerts traction on the retina during detachment, it can cause a retinal tear or full retinal detachment. Retinal detachment is an ophthalmic emergency requiring immediate treatment to prevent permanent vision loss.
Diagnosis of Vitreous Conditions
Ophthalmologists use several techniques to examine the vitreous body:
- Slit-lamp examination: Assessment of the anterior vitreous using a slit lamp
- Ophthalmoscopy (funduscopy): Evaluation of the vitreous and retina after pupil dilation
- Optical coherence tomography (OCT): High-resolution cross-sectional imaging of the vitreous and retina
- Ultrasound (B-scan): Particularly useful when direct visualization is limited due to media opacities
Treatment of Vitreous Conditions
Treatment depends on the underlying condition:
- Floaters: Usually no treatment is required. In cases of significant visual impairment, laser therapy (laser vitreolysis) or surgical removal of the vitreous (vitrectomy) may be considered.
- Vitreous hemorrhage: Mild hemorrhages are often monitored; extensive hemorrhage may require vitrectomy.
- Retinal tear or detachment: Immediate treatment with laser photocoagulation or surgery (scleral buckling or vitrectomy).
References
- Forrester, J.V. et al. - The Eye: Basic Sciences in Practice. 4th Edition. Elsevier, 2016.
- Sebag, J. - Vitreous: in Health and Disease. Springer Science and Business Media, 2014.
- American Academy of Ophthalmology (AAO) - Posterior Vitreous Detachment, Retinal Breaks, and Lattice Degeneration. Preferred Practice Pattern Guidelines. www.aao.org, accessed 2024.
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