Clinically, vitreous detachment can be diagnosed by biomicroscopy and observance of the posterior vitreous face. In many cases, a Weiss ring, a partial or complete grayish-brown, mobile ring, can be seen on fundus examination and is indicative of a PVD.

Ultrasonographically, PVD appears as a thin, smooth membrane that may retain its attachment to the retina at sites of retinal tears, areas of neovascularization, the optic disc, or the vitreous base. PVD can mimic RD on ultrasound when the posterior hyaloid remains attached to the optic disc; however, there are specific clues that can be used to differentiate these two entities (Fig. 2A) (Table 1). PVD demonstrates significant movement and aftermovement on dynamic B-scan. In cases of inflammation and trauma, PVD may be much less mobile. In this situation, it is usually possible to differentiate PVD from RD based on the reflectivity profiles of the tissues. In the absence of dense VH, PVD appears as a low-to-medium reflective membrane on both A- and B-scan, while RD is always highly reflective.

PVD is visible only at high-gain settings whereas the retina is visible at lowand high-gain settings (Fig. 2B, C). Layering of blood along the surface of a PVD may result in a thickened appearance on B-scan and very high reflectivity on A-scan (Fig. 2D). Therefore, to differentiate a hemorrhagic PVD from RD, it is necessary to examine different portions of the membrane for a decrease in reflectivity suggestive of a vitreous membrane. Posteriorly, both the retina and vitreous membranes can appear as highly reflective structures. Anteriorly, however, the retina is much more highly reflective than vitreous membranes.22 In patients who have vitreous hemorrhage secondary to proliferative vitreoretinopathy (PVR), localization of focal traction on the retina can be the most important diagnostic indicator.

RETINAL DETACHMENT

RDs occur when the neurosensory retina separates from the underlying retinal pigment epithelium. RDs are divided into four main types: rhegmatogenous,

tractional, exudative (serous), and combined tractional/rhegmatogenous retinal detachment.23

Rhegmatogenous Retinal Detachment

Rhegmatogenous RDs are the most common type of retinal detachment and are characterized by the presence of a full-thickness retinal tear. There are three prerequisites for the development of rhegmatogenous RD: liquefaction of the vitreous gel, tractional forces to produce a retinal tear, and a retinal tear that allows fluid access from the liquefied vitreous into the subretinal space.23,24 The annual incidence of rhegmatogenous RDs in the general population of the United States is about 12 cases per 100,000 people (0.01% annual risk). There are about 36,000 cases annually, with anatomic surgical success rates up to 95%.25–27 The major risk factors are high myopia, trauma, cataract surgery, ocular infections, lattice degeneration, and glaucoma.

In the setting of media opacity such as a VH, differentiating PVD from RD sometimes can be challenging (see Table 1). RDs can present with variable mobility, but will always be less mobile than vitreous membranes.28 RDs are highly reflective with a thickened, rope-like appearance and

always have optic disc attachment, while a PVD can retain attachment to the optic disc or be detached completely (Fig. 3A). On A-scan, the retina demonstrates close to 100% reflectivity (Fig. 3B).

Tractional Retinal Detachment

Tractional RDs (TRDs) are the second most common type of RD.26 TRDs can occur because of PVR, penetrating trauma, retinopathy of prematurity, and severe diabetic retinopathy. TRDs occur because of vitreoretinal adhesions that cause mechanical separation of the retina from the underlying RPE causing a retinal detachment. The detachment has a tent-like configuration that does not extend to the ora serrata. On B-scan, TRDs demonstrate reduced mobility compared with rhegmatogenous RDs because of the traction placed on the retina (Fig. 4).29

Exudative Retinal Detachment

Exudative RDs are the result of processes that cause the accumulation of fluid between the retina and the RPE in the absence of a retinal tear.

Fig. 4. Tractional retinal detachment. B-scan shows a thin posterior vitreous detachment (arrows) adherent to tent-like tractional retinal detachments

(arrowheads).

There is a long list of conditions that may cause exudative RDs, including:

Idiopathic exudative vascular conditions such as Coat’s disease, central serous chorioretinopathy and hypertension, inflammatory conditions such as scleritis, Vogt Koyanagi Harada’s syndrome and choroiditis (eg, sarcoid or syphilitic choroiditis)

Neoplastic conditions such as retinoblastoma or choroidal metastasis

Iatrogenic conditions such as excessive photocoagulation or scleral buckling

Exudative RDs can be distinguished clinically from rhegmatogenous detachments by their smooth surface, the absence of rugae, the absence of a retinal tear, and shifting of subretinal fluid with movement to the most dependant part of the eye. B-scan ultrasound will show a smooth, sometimes convex surface and absence of rugae

and retinal breaks. Most importantly on ultrasound, as the patient’s head position is changed, the subretinal fluid will shift to the most dependant portion. Depending on the etiology of the exudation, the B-scan also may pick up choroidal masses or a thickened choroid or sclera (see the articles by Fu and colleagues and Ventura and colleagues, elsewhere in this issue.).

Total Retinal Detachment

Open and closed funnel detachments are total RDs attached at the optic disc at one end and attached anteriorly at the ora serrata. In a closed funnel detachment, the two sides of the retina forming the funnel are stuck together or closed from posterior to anterior, usually because of proliferative vitreoretinopathy. On B-scan, the open funnel retinal detachment appears as a wavy, rope-like membrane of high reflectivity with mild-to-moderate mobility (Fig. 5A). A closed funnel or T-shaped chronic retinal detachment appears as a thickened, highly reflective membrane with complete loss of mobility (Fig. 5B).

Differential Diagnosis

Entities that may be mistaken for RD include suprachoroidal hemorrhage, serous choroidal detachment (CD), and hemorrhagic PVD.8 A suprachoroidal hemorrhage can be differentiated from an RD by the smooth, thick, convex shape, immobility, with little aftermovement on dynamic B-scan. Serous CDs can be smooth, domeshaped, or flat on B-scan, have minimal or absent aftermovement and lack attachment at the optic disc (Fig. 6A).22,30 On diagnostic A-scan, both suprachoroidal hemorrhage and serous CDs show a steep, thick, 100% double-peaked spike on A-scan and are differentiated from RDs that