The vitreous humour, also called the vitreous body, is the clear gel that fills most of the inside of the eye between the lens and the retina. It helps the eye keep its shape, lets light pass through to the retina and is involved in several common eye symptoms, especially floaters and flashes.
Some sources spell the term vitreous humor. British medical writing usually uses vitreous humour.
Structure
The vitreous occupies the large posterior part of the eye. It lies behind the lens and in front of the retina. In an adult eye it accounts for most of the globe's internal volume.
The vitreous is transparent and contains no blood vessels in normal adult eyes. That transparency is essential because light must pass through it before reaching the retina.
Composition
The vitreous is mostly water. NCBI Bookshelf material on vitreous haemorrhage describes the vitreous as about 98 to 99 percent water, with the remainder made up of collagen, hyaluronic acid and electrolytes.
The collagen network helps maintain the gel structure. Hyaluronic acid binds water and contributes to the gel's consistency. Together they allow the vitreous to remain clear while still providing some internal support.
Function
The vitreous has several roles:
- it helps maintain the shape of the eye;
- it provides a clear path for light to reach the retina;
- it supports the relationship between the lens, retina and other internal eye structures;
- it cushions the retina and lens from ordinary movement and minor mechanical stress;
- it forms part of the environment through which oxygen, nutrients and waste products move.
The vitreous is not a muscle and does not focus the eye. Focusing mainly depends on the cornea and lens.
Ageing
The vitreous changes with age. It gradually becomes more liquid and can shrink away from the retina. This process is called posterior vitreous detachment, or PVD.
PVD is common and often not sight-threatening by itself. It can cause new floaters and flashes because strands of vitreous cast shadows on the retina or pull on retinal tissue.
Floaters and Flashes
Floaters are small shapes, spots, strands or cobweb-like shadows that appear to move across vision. They are usually caused by tiny clumps or strands within the vitreous casting shadows on the retina.
Flashes can occur when the vitreous pulls on the retina. Moorfields Eye Hospital explains that flashing may happen when the outer part of the vitreous pulls on light-sensitive retinal tissue.
A few long-standing floaters are common. A sudden increase in floaters, new flashes or a curtain-like shadow in vision needs prompt eye assessment because these symptoms can be linked to a retinal tear or retinal detachment.
Posterior Vitreous Detachment
Posterior vitreous detachment occurs when the vitreous separates from the retina. The National Eye Institute describes sudden floaters and flashes as common symptoms.
Most PVD cases settle without major treatment. The important clinical point is checking the retina, because a tear or detachment can occur when the vitreous pulls away.
Vitreous Haemorrhage
Vitreous haemorrhage is bleeding into the vitreous cavity. It can occur after trauma, retinal tears, diabetic retinopathy, retinal vein occlusion or other retinal disease.
Symptoms can include sudden floaters, hazy vision, dark spots or loss of vision. If the view of the retina is blocked by blood, ultrasound may be used to check for retinal detachment or other problems.
Retinal Detachment Risk
The vitreous is closely related to the retina, so sudden vitreous changes can matter. The National Eye Institute lists sudden new floaters, flashes and a curtain or shadow over the field of vision as warning symptoms of retinal detachment.
Retinal detachment is treated as urgent because delayed treatment can lead to permanent sight loss.
Surgery and Treatment
Vitrectomy is surgery to remove some or all of the vitreous gel. It may be used for problems such as non-clearing vitreous haemorrhage, retinal detachment repair, macular hole surgery, severe infection inside the eye or selected cases of disabling floaters.
Vitrectomy can be sight-saving, but it also carries risks. It is not used for ordinary mild floaters.
See Also
References
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