Around the age of 50 you will likely experience a situation called posterior vitreous detachment. This presents with the phenomenon of intermittent flashes of light and new floaters that can interfere with vision.
This experience can be rather frightening as these symptoms are quite similar to those that occur with a retinal detachment.
The main difference between the two is that retinal detachments are sight-threatening emergencies, and posterior vitreous detachments are a normal occurrence that happens with aging.
Ocular Anatomy
To best understand posterior vitreous detachments, also known as PVD, it will be helpful to have a brief understanding of the eye’s anatomy.
The eye has two major components—the anterior half and the posterior half. The two halves are separated by the crystalline lens.
The anterior half of the eye is filled with a fluid called aqueous humor. Aqueous humor is essentially ultrafiltered blood produced continuously by the ciliary body of the eye.
Aqueous flows into the eye near the equator. It flows around the lens forward where it is then drained through the venous system. This flow of aqueous humor is essentially what creates eye pressure (IOP).
Aqueous humor is important as it provides nutrients to the anterior half of the eye.
The posterior half of the eye is filled with a fluid called the vitreous humor. The vitreous humor is often described as being gel-like, and is primarily composed of water, collagen, and hyaluronic acid.
Unlike aqueous humor, vitreous humor is only produced during development and serves no purpose in the adult eye besides the fact that it keeps the eye turgid. It fills the posterior cavity of the eye and keeps the backmost structure of the eye, the retina, smooth.
It is important that the retina has some pressure to keep it smooth and in place, as the retina contains specialized cells called photoreceptors that are responsible for detecting light and transmitting its signals to the brain for image processing.
The retina is very thin—almost like sticky tissue paper. The vitreous humor is needed to apply pressure to the retina and hold everything where it should be. If anything disrupts the retina so that it is not smoothly held in place, it can affect how light is transmitted, resulting in visual defects, abnormalities, blurriness, and overall decreased vision.
What is a Posterior Vitreous Detachment?
As noted previously, the primary job of the vitreous humor is to provide nutrition during development. After a baby is born, it no longer provides nutrition and its only job becomes structural support to the retina.
Over many years, the components of the vitreous begin to break down in a process called syneresis. The once somewhat solid gel begins to break down with water pockets, and the entire structure condenses to take up less space.
As the vitreous humor condenses, it pulls away from the retina, creating a posterior vitreous detachment.
The entire process of a posterior vitreous detachment takes about 1 month.
Flashes can occur when the vitreous humor pulls on the retina as it tries to detach. The traction between the vitreous humor and the retina causes the photoreceptors to fire. The brain interprets this as a presence of light—hence the flashing phenomenon.
Floaters are created in several different ways during this process.
Firstly, collagen fibers can be trapped in the water pockets created during syneresis. As the collagen fibers “float” around these little pockets, they interfere with the transmission of light and therefore the brain processes these as what we know as “floaters”.
Secondly, there are times when the vitreous humor pulls on the retina during its separation and can pull a small chuck of retinal tissue with it. Generally, this is not an issue. However, the small piece of retinal tissue “floats” within the vitreous humor, again interfering with the transition of light and are registered by the brain as floaters.
Typically, these types of floaters are a little larger in size than the collagen floaters and are therefore much more noticeable by the individual.
Complications of a PVD
While posterior vitreous detachments will eventually happen to everyone, there are some circumstances where they can cause serious problems.
One such problem is retinal detachment. Retinal detachments occur in under 10% of PVDs, but can occur. Therefore, it is helpful to know what signs to watch for and to always go see your local optometrist as soon as possible if something does not seem right.
As the vitreous humor pulls away from the retina, it can pull on more than just a small chunk. Sometimes the adherence between the vitreous humor and retina is so great that the vitreous actually tears the retina away as it tries to separate.
When this occurs, the patient will note hundreds of tiny floaters in their vision—almost like someone pouring pepper into their vision.
Non-stop flashes may also occur as the retina flaps to-and-fro.
A curtain, veil, or loss of part of the vision is another significant sign of retina detachment, as this again indicates part of the retina is flapping in toward the vitreous.
If any of these symptoms occur, it is of utmost importance to get into your eye doctor ASAP, as retinal detachments are medical emergencies that need to be treated quickly in an attempt to save your vision.
A second complication of posterior vitreous detachment is vitreous hemorrhage. Like retinal detachments, sometimes the adherence between the vitreous humor and blood vessels within the retina are very strong. As the vitreous humor attempts to separate from the retina, sometimes it can nick retinal blood vessels, causing blood to pour into the vitreous humor.
Vitreous hemorrhages present very similarly to retinal detachments—with hundreds of small floaters in a person’s vision.
Your body will eventually reabsorb the blood and vision will return to normal. However, your doctor will want to evaluate you closely to ensure that only a blood vessel was sheared, as many times vitreous hemorrhages go hand-in-hand with retinal detachments.
The final complication discussed here is an epiretinal membrane (ERM). When the vitreous pulls away from the retina, sometimes special cells called glial cells will remain along the surface of the retina.
These cells begin to replicate and can bunch up on the retina. This creates small wrinkles in the retinal tissue.
Typically, ERMs will not affect vision, but some can proliferate significantly, resulting in an overall decrease in vision. When this occurs, a membrane peel may be needed to remove the glial growth from the retina to improve vision.
While complications listed here are not common, they do occur. If you, or someone you know, is experiencing any of the symptoms listed here, it is best to get in to see your eye doctor as soon as possible to ensure nothing serious is going on.
Your doctor will likely monitor your retina over the course of a month or two to ensure none of these problems occur while the vitreous detaches. Once the vitreous has completely separated from the retina, the risk of these events occurring drastically decreases to less than 5%.
