What is Vitreous Humor?
The vitreous humor is the clear gel-like fluid that fills the vitreous chamber, the space between the eye lens and the retina. Sometimes it’s referred to as a vitreous body, vitreous fluid, or simply vitreous. The fluid is made up of about 98 percent water and trace amounts of hyaluronic acid, glucose, collagen, proteins, and salts.1
The vitreous fluid is transparent to allow light to pass through to the retina, enabling clear vision. The retina is the layer of tissue in the back of the eye with photosensitive cells that receive light signals. They send them to the brain through the optic nerve for interpretation.
Vitreous Humor Functions
The main function of the vitreous body is to maintain the eye’s round shape. It does this by creating fluid pressure within the eye (intraocular pressure).
The vitreous humor also enables visual clarity. Its clear nature allows light to pass through to the retina when you focus on an object.
Even further, the vitreous humor functions as a shock absorber during head trauma or rapid head movements that may disturb the eye or cause damage to the inner parts of the eye.
Where is the Vitreous Humor Located?
The vitreous fluid is located in the vitreous chamber, the largest among the three chambers of the eye—anterior (between cornea and iris), vitreous, and posterior (between iris and lens). This makes the vitreous humor the most prominent fluid in the eye, occupying about 80 percent of the eyeball’s volume.2
The vitreous structure is surrounded by a layer of collagen fibrils known as vitreous cortex, vitreous membrane, or hyaloid membrane. This membrane separates it from the rest of the eye structure.
Be sure not to confuse vitreous humor with aqueous humor. The latter is located in the anterior chamber of the eye.
Associated Conditions & Treatments
Aging may cause significant changes in vitreous fluid. These changes can lead to eye conditions, some of which may threaten sight.
Let’s look at the most common conditions of vitreous humor:
1. Vitreous Degeneration (vitreous syneresis)
Vitreous degeneration is age-related thinning of the vitreous fluid. In younger people, the fluid is thick and gel-like, filling the entire chamber. The aging process causes gradual liquefying and thinning of this fluid.
Vitreous degeneration is prevalent among people aged 50 or older. Other common causes may include:
- Previous cataract surgery
- Eye trauma
- Myopia (nearsightedness)3
When the fluid thins and liquefies, it’s unable to fill the vitreous chamber. This may lead to posterior vitreous detachment (PVD), a condition characterized by sagging and pulling away of the vitreous fluid from the retina. Common symptoms include the presence of vitreous floaters, flashes, streaks, and retinal shadows.
Treatment
There’s no specific treatment for vitreous degeneration. The symptoms usually clear off or become less bothersome. Most people get used to vitreous floaters after a few months.
For reference, vitreous floaters are tiny collagen fibers that clump up and form what appear as blurry shadows across your vision.4
In cases of severe vitreous hemorrhage, vitreous floaters, and retinal tears, your doctor may recommend a surgical procedure called vitrectomy. Vitrectomy involves removal of the vitreous humor and replacement with a substitute such as silicone oil, heavy oil, or hydrogel.5
2. Posterior Vitreous Detachment (PVD)
PVD occurs when the vitreous fluid separates from the retina. This condition is common among older adults.
According to current research, the prevalence rate of PVD is 24 percent among people aged 50 to 59 years and 87 percent among those aged 80 to 89 years.6
Common causes include:
- Eye trauma
- Eye surgery
- Diabetes
- Nearsightedness
Someone with PVD will experience floaters and flashes across their vision. Although these symptoms can be bothersome, PVD is neither painful nor sight-threatening.
Severe cases of PVD can result in more serious conditions like retinal tears or retinal detachment.
Treatment
There is no specific treatment for PVD. Most people get used to floaters in their visual field. The flashes tend to improve with time. However, several treatment options are available in case of complications such as retinal tears or detachment.
3. Retinal Tears and Retinal Detachment
A retinal tear is when a section of the retina partly detaches from its normal position at the back of the eye. It may occur alongside posterior vitreous detachment (PVD).
Complete detachment of the retina separates it from the layer of cells and vessels that provide it with oxygen and nourishment.
Common causes include:
- Aging
- Family history
- Previous detachments
- Severe myopia
- Severe eye injury
- Eye diseases such as retinoschisis or uveitis
Studies show that the annual incidence of retinal detachments in the United States is one in 10,000, with males being at higher risk than females.7
If left untreated, retinal detachment may lead to the appearance of floaters and reduced vision.8 This is a sight-threatening condition and requires urgent medical attention.
Treatment
If you’re diagnosed with a retinal tear or detachment, your doctor may recommend surgery. Common surgical procedures for retinal tears include:
- Photocoagulation. Laser beams are used to repair torn parts.
- Freezing (cryopexy). A freezing probe is used to create a scar on the tear, which helps secure the retina in position.
Common surgical procedures for retinal detachment include:
- Vitrectomy. Removing and replacing the vitreous fluid.
- Scleral buckling. Placement of a band/buckle on the sclera (white of the eye) to hold the retina in position.
- Pneumatic retinopexy (PR). Injecting air or gas into the vitreous cavity to increase its volume and allow reattachment of the retina to the eyeball.9
4. Vitreous Hemorrhage (VH)
The vitreous chamber contains many blood vessels supplying oxygen nourishment. Some conditions, such as diabetic retinopathy or retinal vein occlusion (RVO), may damage blood vessels, causing them to rupture and bleed into the vitreous humor.
Other causes include:
- Bleeding due to retinal tears or detachment
- Trauma to the eye
- Abnormal blood vessels
- Damaged normal blood vessels
- Eye surgery
Vitreous hemorrhage is not painful and may appear as dark spots or blurriness in your vision. The annual incidence rate of vitreous hemorrhage is about 7 cases per 100,000 people. Timely treatment is important to avoid complications.
Treatment
Most cases of VH do not require treatment as the blood can clear off from the vitreous fluid with time as long as there is no further damage. However, severe cases may necessitate the following procedures:
- Laser photocoagulation. Treats abnormal or leaky blood vessels and repairs retinal damage.
- Anti-VEGF injections. Shrink abnormal blood vessels in the eye.
- Cryotherapy. Use of low temperatures to treat tears and detachments that cause bleeding.
- Vitrectomy. Replacing the bloody vitreous humor with a substitute fluid.
Your eye doctor can check for vitreous abnormalities as part of a dilated eye exam.
Seek immediate medical attention if you experience floaters, flashes, vision changes, or severe eye pain as these may indicate a potential problem.
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