PMC3261320_01
Optical coherence tomography images of the macula of the right eye obtained (A) 30 months and (B) 18 months before and (C) 1 day after symptomatic posterior vitreous detachment. At 30 months prior, the posterior hyaloid face (arrows) appears detached peripheral to the macula. At 18 months prior, the vitreous shows a shallow detachment, including over the macula. After becoming symptomatic, the vitreous is fully separated from the retinal surface in the perimacular region.
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F2
OCT images (Fig. 2) acquired 30 and 18 months prior to PVD showed progressive but asymptomatic shallow, partial detachment of the vitreous in the perimacular area.
Conventional 10-MHz B-mode images obtained 1 day (left) and 3 months (right) after posterior vitreous detachment. Images are in a horizontal plane, with nasal aspect to image right. The hyaloid face (H) and kinetically mobile inhomogeneities (decreasing in brightness after 3 months) within the vitreous body can be seen in both images, but with limited detail, especially in the anterior vitreous.
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Conventional 10-MHz B-mode ultrasound (Fig. 3) acquired on day 1 and at 3 months revealed incomplete detachment of the vitreous body with a region of traction nasally.
Synthetically focused image obtained with the annular array using 20-MHz monocycle excitation. Scanning was in a horizontal plane. The increased depth-of-field and the rectilinear image format resulting from linear scanning (as opposed to the more familiar sector scan common with 10-MHz probes) allows improved depiction of anterior segment structures. Nevertheless, high attenuation at 20 MHz leads to reduced sensitivity in depicting the faintly reflective structure of the vitreous body.
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An image obtained with the array using a single 20-MHz cycle for excitation (Fig. 4) demonstrated increased resolution and depth-of-field compared with conventional 10-MHz images, but inadequate sensitivity for evaluation of the vitreous body.
Synthetically focused images obtained using chirp excitation, with scanning in a horizontal plane avoiding the lens, nasal aspect to image right. Chirp excitation produces a significant enhancement in signal-to-noise ratio compared with monocycle excitation. The diffuse halo seen around brightly reflecting structures (vitreoretinal interface and anterior segment) is an artifact due to incomplete suppression of side lobes by the compression filter because of signal saturation.
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F5
With chirp excitation (Fig. 5), high resolution and depth-of-field were achieved along with high sensitivity in depiction of the vitreous body.