What Is Posterior Vitreous Detachment?
Posterior vitreous detachment has traditionally been regarded as an agerelated degenerative process of the vitreous that Results in the separation of the cortical vitreous gel from the retinal surface. The process is usually preceded by liquefaction and cavity formation of normal vitreous gel. When the thinned pre-retinal vitreous cortex ruptures completely, synchetic fluid from the vitreous body empties into the retrohyaloid space, separating the cortical gel from the internal limiting membrane (ILM) of the retina.
The hypothesis that PVD is purely an age-related degenerative process relating to vitreous syneresis, however, is not wholly supported by clinical experience. For example, not all elderly patients develop a PVD, and children can still develop PVD-related retinal tears. The hypothesis also does not explain the interesting occurrence of a PVD in some previously vitrectomized eyes.
More recent studies have suggested that true PVD is distinct from mere cortical gel collapse. In a study by Snead et al, the presence of type IV collagen in the posterior aspect of detached vitreous in a group of elderly patients with physiological PVD was demonstrated.[6,7] This is supported by the demonstration of a distinct membrane, also called the posterior hyaloid membrane, which is a separate entity from the detached cortical gel in clinical and histological examination (Figure 1). True PVD therefore represents the separation not only of cortical gel but also of the posterior hyaloid membrane (PHM) from the retinal surface. This membrane may also separate in eyes in which the cortical gel has been removed at vitrectomy, as mentioned above (Figure 2). It is only with the occurrence of true PVD that an eye is at risk for retinal tears.
A and B: Characteristic appearance of posterior hyaloid membrane (PHM) in an eye with posterior vitreous detachment as seen on slit-lamp examination. C: Histology of detached PHM showing a distinct membrane (arrowheads) covering the posterior surface of the residual vitreous cortex with spindle-shaped cells visible (arrows) along the membrane. D: Higher power view of the PHM showing a spindle-shaped cell.
Detached posterior hyaloid membrane in an eye that had previously undergone vitrectomy.
The presence of type IV collagen suggests that the PHM represents delamination of part of the ILM of the retina. Therefore, in an eye without PVD, the PHM is apposed against the basement membrane of the Müller cells. Together, they form the light, microscopic ILM. The process of PHM separation from the retina is incompletely understood, but evidence suggests it may be an active process involving the cellular component of the PHM; this, however, is yet unproven.
The time required for the process of PVD to complete is also currently unknown and probably varies from patient to patient. In a recent study using optical coherence tomography (OCT), however, there is evidence to suggest that the process occurs in stages and can take years to complete.
© 2005 Comprehensive Ophthalmology Update, LLC
Cite this: Posterior Vitreous Detachment: Current Concepts and Management - Medscape - Jul 01, 2005.