| Posterior vitreous detachment | |
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Schematic diagram of the human eye. |
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| DiseasesDB | 31271 |
A posterior vitreous detachment (PVD) is a condition of the eye in which the vitreous humour separates from the retina.
Broadly speaking, the condition is common for older adults and over 75% of those over the age of 65 develop it. Although less common among people in their 40s or 50s, the condition is not rare for those individuals. Some research has found that the condition is more common among women.[1][2]
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The vitreous (Latin="glassy") humour fills the eye behind the lens. At birth it is attached to the retina. Over time the vitreous changes, shrinking and developing pockets of liquefaction, similar to the way a gelatin dessert shrinks, or detaches, from the edge of a pan over time. At some stage the vitreous may peel away from the retina. This is usually a sudden event, but may also occur slowly over months.
Several studies have found a broad range of incidence of PVD, from 20% of autopsy cases to 57% in a more elderly population of patients (average age was 83.4 years). Age and refractive error play a role in determining the onset of PVD in a healthy person. PVD is rare in emmetropic people under the age of 40 years, and increases with age to 86% in the 90s. People with myopia (nearsightedness) greater than 6 diopters are at higher risk of PVD at all ages. Posterior vitreous detachment does not directly threaten vision. Even so, it is of increasing interest because the interaction between the vitreous body and the retina might play a decisive role in the development of major pathologic vitreoretinal conditions, such as epiretinal membrane.
When this occurs there is a characteristic pattern of symptoms:
As a posterior vitreous detachment proceeds, adherent vitreous may pull on the retina. While there are no pain fibers in the retina, vitreous traction may stimulate the retina, with resultant flashes that can look like a perfect circle.
The vitreous is more firmly attached to the retina anteriorly, at a structure called the vitreous base. The vitreous does not normally detach from the vitreous base, although it can be detached with extreme trauma. PVD may also occur in cases of cataract surgery, within weeks or months of the surgery.
However, the vitreous base may have an irregular posterior edge. When the edge is irregular, the forces of the vitreous peeling off the retina can become concentrated at small posterior extensions of the vitreous base. Similarly, in some people with retinal lesions such as lattice retinal degeneration or chorio-retinal scars the vitreous may be abnormally adherent to the retina. If enough traction occurs the retina may tear at these points. If there are only small point tears, these can allow glial cells to enter the vitreous and proliferate to create a thin epiretinal membrane that distorts vision. In more severe cases, vitreous fluid may seep under the tear, separating the retina from the back of the eye, creating a retinal detachment. Trauma can be any form from a blunt force trauma to the face such as a boxer's punch or even in some cases has been known to be from extremely vigorous blowing of the nose. If a retinal vessel is torn, the leakage of blood into the vitreous cavity is often perceived as a "shower" of floaters. Retinal vessels may tear in association with a retinal tear, or occasionally without the retina being torn.
The risk of retinal detachment is greatest in the first 6 weeks following a vitreous detachment, but can occur over 3 months after the event.
Prompt examination of patients experiencing vitreous floaters combined with expeditious treatment of any retinal tears has been suggested as the most effective means of preventing certain types of retinal detachments.[3] The risk of retinal tears and detachment associated with vitreous detachment is higher in patients with myopic retinal degeneration, lattice degeneration, and a familial or personal history of previous retinal tears/detachment.