Posterior vitreous detachment
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The vitreous humor 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. When this occurs there is a characteristic pattern of symptoms:
- flashes of light (photopsia)
- a sudden dramatic increase in the number of floaters
- a ring of floaters or hairs just to the temporal side of the central vision
- a slight feeling of heaviness in the eye.
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.
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.
However, the vitreous base may have an irregular posterior edge. When the edge is irregular, the forces of the vitreous peeling off the retinal 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. 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. 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.
- Byer NE. "Natural history of posterior vitreous detachment with early management as the premier line of defense against retinal detachment." Ophthalmology. 1994 Sep;101(9):1503-13; discussion 1513-4. PMID 8090453.