tear, which can be accompanied by bleeding that may extend into the vitreous cavity causing

VH.36,37

PEDs usually are asymptomatic, but if the foveal area is involved, the patient can complain of blurred vision and visual distortion. Clinically, PEDs are detected on fundus examination and are characterized best by optical coherence tomography (OCT).38 The role of ultrasonography in this setting is helpful in cases where VH is obstructing the view of the posterior segment. On B-scan, PEDs appear as a thick, nonmobile, dome-shaped membrane with high reflectivity on A-scan (Fig. 8).39

RETINOSCHISIS

Retinoschisis involves splitting of the sensory retina into inner and outer layers, with the formation of cystic spaces between layers.40 Retinoschisis occurs in two forms: degenerative and juvenile. Degenerative retinoschisis is an idiopathic, age-related process with a prevalence of 0.7%, and is found most frequently in the inferotemporal quadrant.41 Juvenile retinoschisis is a X-linked retinal dystrophy that typically presents in school-age children.

Both retinoschisis and RD are highly reflective on B-scan, but retinoschisis is usually of lower amplitude and is thinner than RD.9 Retinoschisis can be differentiated from RD by its focal, smooth, dome shape (Fig. 9A). Retinoschisis is differentiated from CD by its thinner appearance on B-scan and a single peak on A-scan, while a CD has a double peak (Fig. 9B). The diagnosis of retinoschisis can be aided by OCT imaging, which

shows the splitting of the retina with cystic spaces between the two layers.42

DISCIFORM LESIONS

Disciform lesions typically are characterized by irregular structure and mainly high reflectivity. On B-scan, disciform lesions appear as an elevation of the retina that may be calcified in long-standing lesions (Fig. 10).12 Over time, the height of the lesion usually will decrease.43 Ultrasonography is useful in the setting of a large, peripheral disciform lesion that may be confused with a choroidal melanoma (see the article by Fu and colleagues, elsewhere in this issue).

POSTSURGICAL CHANGES

Scleral Buckle

Scleral buckles produce a convex indentation of the ocular wall and strong sound attenuation because of the extremely high reflectivity of the buckling material (Fig. 11). A clue to the presence of a scleral buckle is the encircling band, which often will produce a lower elevation peripheral to the buckle. The ultrasonographic appearance of the scleral buckle can vary significantly based upon the type of material used for the buckle.

MIRAgel Implant

A hydrogel implant (MIRAgel, MIRA, Walthem, Massachusetts) commonly was used for scleral buckling in the 1980s and early 1990s. Because of its physical properties, the implant would swell extensively over time (over 10 years), causing conjunctival bulging, limitation of ocular motility, diplopia, ocular pain, ocular inflammation, and protrusion of the implant.44,45 Rarely, the swollen

Fig. 11. Scleral buckle. B-scan showing scleral indentation (arrowhead, B-scleral buckle).

Fig. 12. MIRAgel implant. B-scan longitudinal view showing intrusion of the retina, choroid, and very thin sclera (arrowhead). Swelling of the buckle (M) can be seen, with associated orbital shadowing from the buckle.