High-resolution ultrasonic imaging and characterization of the ciliary body.

PURPOSE: To develop a means for noninvasive in vivo visualization of the ciliary processes using very-high-frequency (50 MHz) ultrasound and to develop quantitative morphologic descriptors that may relate to physiologic function. METHODS: The region of the ciliary body was scanned with very-high-frequency ultrasound, both in rabbits and in normal human subjects. Data were acquired in a series of planes so that the spacing between them was less than the beam width of the transducer in its focal plane. Three-dimensional perspective images were constructed, representing the anatomy of the angle region, including the ciliary processes. The automatically detected boundaries of the ciliary processes were analyzed to compute their periphery, area, shape factor, and fractal dimension. These measures were compared between the human and the rabbit eye and analyzed for periodicities related to the spacing of successive processes. RESULTS: Three-dimensional images allowed visualization of the radial arrangement of the processes. All biometric descriptors were significantly different between the rabbit and human eye and showed periodicities consistent with spacing between processes. CONCLUSIONS: The methods described in this report are sensitive descriptors of the state of the ciliary processes. These techniques may be of value in measurement of changes in the ciliary body associated with disease, medical therapy, and aging.

Arc-scanning very high-frequency digital ultrasound for 3D pachymetric mapping of the corneal epithelium and stroma in laser in situ keratomileusis.

PURPOSE: To test and demonstrate measurement precision, imaging resolution, 3D thickness mapping, and clinical utility of a new prototype 3D very high-frequency (VHF) (50 MHz) digital ultrasound scanning system for corneal epithelium, flap, and residual stromal thickness after laser in situ keratomileusis (LASIK). METHODS: VHF ultrasonic 3D data was acquired by arc-motion, meridional scanning within a 10-mm zone. Digital signal processing techniques provided high-resolution B-scan imaging, and I-scan traces for high-precision pachymetry in 4 eyes. Thickness maps of individual corneal layers were constructed. Reproducibility of epithelial, flap, and full corneal pachymetry was assessed for single-point and 3D thickness mapping by repeated measures. Thickness mapping of the epithelium, stroma, flap, and full cornea were determined before and after LASIK. Preoperative to postoperative difference maps for epithelium, flap, and stroma were produced to demonstrate anatomical changes in the thickness profile of each layer. RESULTS: Surface localization precision was 0.87 microm. Central reproducibility for single-point pachymetry of epithelium was 0.61 microm; flap, 1.14 microm; and full cornea, 0.74 microm. Reproducibility for central pachymetry on 3D thickness mapping was 0.5 microm for epithelium and 1.5-microm for full cornea. B-scans and 3D thickness maps after LASIK demonstrated resolution of epithelial, stromal component of the flap, and residual stromal layers. Large epithelial profile changes were demonstrated after LASIK. Topographic variability of flap thickness and residual stromal thickness were significant. CONCLUSIONS: VHF digital ultrasound arc-B scanning provides high-resolution imaging and high-precision three-dimensional thickness mapping of corneal layers, enabling accurate anatomical evaluation of the changes induced in the cornea by LASIK.

Three-dimensional ultrasound imaging. Clinical applications.

OBJECTIVE: The aim of this report is to describe the technology of three-dimensional (3-D) ultrasonic imaging and its impact on improved diagnosis and monitoring of ocular disease. DESIGN: The authors reviewed techniques for acquiring and displaying 3-D ultrasound data of the eye. PARTICIPANTS: The authors applied these techniques to representative individual cases, including a choroidal hemorrhage, a ciliary body melanoma, a ciliary body detachment, a displaced posterior chamber intraocular lens, and topographic analysis of a normal cornea. INTERVENTION: A computer-controlled motion system was used to perform very high-frequency (VHF) (50-MHz) and conventional (10-MHz) digital 3-D ultrasound data collection. The scanning system allowed digitization of ultrasound data from a series of parallel planes. The 3-D data could be manipulated interactively to obtain two-dimensional images in any plane through the scan volume. The 3-D images were constructed by volume rendering and could be positioned for viewing from a variety of perspectives. The 3-D ultrasound parameter images representing acoustic scatterer properties were generated by spectrum analysis of digitized echo data. Color maps representing the contour and thickness of the epithelium and stroma of the central corneal were generated by digital signal processing of 3-D echo data. RESULTS: Quantitative volume measurement and biometric techniques enhanced the diagnostic and treatment planning information content in 3-D ultrasound images. The location and extent of hemorrhage and clots within the suprachoroidal space were shown with solid modeling. Volume changes in ciliary body melanoma over time were documented and 3-D ultrasound parameter image changes associated with radiation therapy observed. In ciliary body detachment, the extent of the detachment was shown. Solid modeling of a posterior chamber intraocular lens showed misplacement of the haptic in relation to the lens capsule remnants. Keratopachymetric maps showed the range and variance of thickness and local radius of curvature measurements in the cornea. CONCLUSIONS: Quantitative volume measurement and biometric tools combined with segmentation of 3-D ultrasound images improve diagnostic and treatment planning informational content of 3-D ultrasound images through improved localization of tissue structures.

Ultrasonic evaluation of the vitreous and retina.

Ultrasonic evaluation of the vitreous body augments and complements visual and clinical assessment in any condition in which some form of media opacity exists, eg, cornea, lens, hemorrhage, or subretinal mass. The appearance of the eye in hypotony, the presence of foreign material, the pattern of hemorrhage, and the presence of a detached retina or choroid are all identifiable and their diagnosis may be of critical importance to patient management. Patterns of diabetic retinopathy and ocular tumors are usually characteristic using conventional 10 MHz ultrasound. The use of Very High Frequency (VHF or UBM) ultrasound can identify ciliary body detachment or other retroiridal pathology, such as tumors and cysts.

Correlation of ultrasound parameter imaging with microcirculatory patterns in uveal melanomas.

Previous studies demonstrated a correlation between acoustic backscatter parameters and survival in ocular melanoma. The histologic presence of microvascular networks in ocular melanoma is also associated with death from metastases. This study tests the hypothesis that melanomas grouped on the basis of these microvascular patterns are separable by ultrasound spectrum analysis. We scanned 40 melanomas using a 10-MHz ultrasound unit equipped for digitization of radio frequency data. After enucleation, tumors were sectioned in planes corresponding to the ultrasonographic examination and stained to demonstrate microcirculation. Acoustic spectral parameters were compared between 14 melanomas with a nevuslike microcirculation and 26 with foci of high-risk microvascular structures. Smaller scatterer size, lower acoustic concentration and greater spatial variability were found to correlate with high-risk microvascular patterns and areas of cystic degeneration. We suggest that nonvascular extracellular matrix components associated with microvessels may be responsible for the correlation of acoustic parameters with microvascular pattern and distribution.

High frequency ultrasound evaluation of radial keratotomy incisions.

Radial keratotomy is a surgical procedure to correct myopia that involves placing corneal incisions of precise partial thickness to induce flattening. It has yielded positive but sometimes unpredictable results. Many surgical variables influence the final result. Among them, incision depth is probably the most difficult to control and evaluate. In this study, we used very high frequency (50 MHz) ultrasound (HFU) to image radial keratotomy incisions in post-radial keratotomy human corneas to obtain high definition images of the cornea. The images allowed us to measure the depth of incisions as a percentage of corneal thickness.