posterior vitreous detachment
Posterior vitreous detachment (PVD), also known as hyaloid detachment, occurs when the retinal layer and vitreous body/posterior hyaloid membrane dissociate, with an intervening fluid collection forming in the subhyaloid space. It is thought to be a common consequence of aging, occurring in more than 70% of the population over the age of 60 .
PVD is the most common cause of sudden onset "floaters" in one's visual field, most correctly referred to as "vitreous condensations" in this context. It also may cause photopsia, exacerbated by eye movements.
The sonographic appearance of isolated posterior vitreous detachment includes the following characteristics :
- linear, echogenic membrane in the posterior compartment
- thickening may be observed in the presence of hemorrhage or inflammation
- may demonstrate tethering near the ora serrata
- point of attachment referred to as the vitreous base
- freely mobile with oculokinetic ultrasonography
- unlike retinal detachment, the membrane will cross the intersection of the optic nerve sheath and posterior wall of the globe
- in the acute stages, PVD should demonstrate prominent "after movements" that are more prominent than what would be expected from retinal/choroidal detachments
- mobility may be lost over time, making the differentiation from other vitreous pathologies difficult
- may be associated with other pathologic findings, including;
- retinal detachment
- vitreous hemorrhage