When it comes to the eye, many individuals hear the word “detachment” and immediately get nervous. This is because a retinal detachment, while rare, can be a blinding event.
Yet, almost everyone will undergo a process called a posterior vitreous detachment, or PVD. Therefore, when you talk to your eye doctor and are told you have a posterior vitreous detachment, it is typically of no serious consequence. This article will aim to explain what a posterior vitreous detachment is, and how to differentiate it from a more serious problem like a retinal detachment.
Anatomy of the Eye
To understand what a posterior vitreous detachment is, it is best to understand what exactly the vitreous is.
The eye has two major compartments—the anterior chamber (the front half of the eye) and the posterior chamber (the back half of the eye).
The anterior chamber and posterior chamber are roughly separated by the lens of the eye located near the equator.
The anterior chamber is bound by the frontmost structure of the eye—the cornea. The posterior chamber is bound by the backmost structure of the eye—the retina.
The retina is essentially the most important part of the eye. It contains specialized cells called photoreceptors that detect light and then transmit signals to the brain for image processing. This is why retinal detachments are scary—if the retina detaches and dies off, the eye will no longer be able to detect light and thus will not transmit signals to the brain and no vision will be produced.
The anterior chamber continuously has a liquid called aqueous humor pumped into it. Aqueous humor is made from ultrafiltered blood plasma and is pumped into the eye near the lens. Aqueous humor flows from the equator of the eye toward the front of the eye where it is then drained out back into the blood system, creating a continuous cycle of aqueous humor flow.
The posterior chamber, on the other hand, is filled with a fluid called vitreous humor. Vitreous humor is produced once—during fetal development.
During development the vitreous humor provides nutrients to the growing eye structures. Once the eye is developed, the vitreous humor’s only role is to provide structural support to the eye.
Vitreous humor is comprised primarily of water, but also collagen and hyaluronic acid. It is contained within the posterior chamber by a thin collagen membrane called the hyaloid membrane.
This membrane adheres to several different points in the back of the eye including the ora serrata, optic nerve, retinal blood vessels, and macula (the area of the retina responsible for your sharpest central vision).
What is a Posterior Vitreous Detachment?
As stated above, the vitreous humor is created once—during fetal development. As we age, the components of the vitreous (water, collagen, and hyaluronic acid) begin to separate and shrink up in a process called liquefaction. Think about this like an old balloon. While the balloon is still intact, if left untouched for several days it starts to shrink up and change shape.
When the vitreous shrinks up, it pulls away from its attachment points—the optic nerve, retinal blood vessels, and macula—until the vitreous ultimately detaches completely from the retina.
Anytime the vitreous pulls on the retina, it artificially stimulates the photoreceptors (light detecting cells of the retina) resulting in the appearance of “flashing lights”. Therefore, the appearance of flashing lights in vision may indicate that you are undergoing a posterior vitreous detachment.
In most cases, this process occurs easily and without problems. In other cases, however, the attachment between the vitreous and the retina is strong and the vitreous pulls and rips part of the retina with it.
Typically, if this occurs, the vitreous will only take a very small piece of the outer layer of the retina and no serious damage occurs. In these situations, the patient may note the appearance of a large “floater” in his or her vision, as a little piece of retinal tissue is now floating around in the vitreous humor, interfering with the pathway of light to the retina.
In other cases, the vitreous humor may be firmly attached to the retinal blood vessels. When it pulls away it can shear the blood vessel, resulting in the leakage of blood from the vessel into the vitreous—AKA a vitreous hemorrhage.
Vitreous hemorrhages secondary to posterior vitreous detachments will appear to the patient as hundreds of little black dots in his or her vision—almost like someone is pouring pepper into the eye. The blood itself is not a major concern—over time gravity will pull the blood cells down toward the bottom of the eye, where the blood will be reabsorbed by the body.
What is of concern with vitreous hemorrhages is that they are often an indication that the vitreous detachment has created a retinal break.
Retinal Tears and Breaks
Retinal breaks secondary to posterior vitreous detachment are not common, however they can occur if the vitreous pulls hard enough on the retina to actually rip it—creating a retinal hole or tear (i.e. break in the retina).
Retinal breaks significantly increase the risk of retinal detachment, as the integrity of the retina is now jeopardized. If a retinal break occurs, your doctor may recommend you undergo a laser treatment to tac the retina back down into place, preventing a retinal detachment from occurring.
Therefore, anytime a person sees a drastic increase in new floaters, or hundreds of black dots in his or her vision (indicating a vitreous hemorrhage) it is best to get in to see your eye doctor immediately so they can assess the situation to determine if there is a retinal break, or even a retinal detachment, to get you the appropriate treatment.
Other signs that something more serious may be going on include a curtain or veil moving across your vision, loss of a portion of your vision (ex. cannot see anything above the eyebrows), and non-stop flashing lights in your vision. If any of these symptoms occur, call your eye doctor immediately as they could indicate a retinal detachment.