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O ptical C oherence T omography & U ltrasound B io M icroscopy of the anterior segment of the eye minoo afshar M.D. O ptical C oherence T omography (OCT).
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OpticalCoherenceTomography & UltrasoundBioMicroscopy of the anterior segment of the eye minooafshar M.D
Optical Coherence Tomography (OCT) • Optical Coherence Tomography (OCT) is a new medical diagnostic imaging technology which can perform micron resolution cross-sectional or tomographic imaging in biological tissues (resolutions in the range of 3 to 20 micro m) • The operation of OCT is analogous to ultrasound B-mode imaging or radar except that light is used rather than acoustic or radio waves
OpticalCoherenceTomography • “Optical" refers to the fact that a beam of light (typically in the near-infrared spectrum) is used to scan the sample of interest • When the time-of-flight delay of the reference mirror matches the sample reflection of a certain depth, they interfere coherently and produce a signal that could be detected • Tomography means cross-sectional imaging
Optical coherence tomography (OCT; Visanteby Carl ZeissMeditec) generates a two-dimensional image from a reflected light beam. The principle is similar to that of B-scan ultrasonography but uses light instead of sound, is non-contact, and provides higher resolution pictures. OCT is wavelength dependent: 1310 nm is optimal for anterior segment imaging (Visante) whereas 820 nm is best for retinal imaging (Stratus, Cirrus). The reason for this is 1310 nm has better water absorption, which decreases retinal exposure. Therefore, more power can be used safely; there is faster scanning (minimizes motion artifact), reduced scattering, and improved penetration into turbid tissue such as sclera, iris, angle, and opaque corneas. The Visante can image and measure all anterior segment tissues: cornea (thickness, LASIK flaps, incisions, wounds, dystrophies, scars), iris (tumors, trauma), angle (angle-closure glaucoma assessment, trabeculectomy patency, drainage device positioning), and lens (cataract location, implant position, accommodative IOL movement).
OCT is useful in a wide range of corneal and anterior segment applications • LASIK • Intacs • Corneal Scar & PTK • Biometry for Phakic IOL • Corneal Power & IOL Power Calculation • Keratoconus • Tear Meniscus • Narrow Angle Glaucoma
OCT The Visante OCT system has many clinically practical uses for the anterior-segment surgeon, including: • Angle assessment • Pachymetry • Glaucoma surgery evaluation • Evaluation of corneal transplant • Visualization of the sclera,suprachoroidal space • Identification of iris lesions • Evaluation of crystalline lens, pseudophakic IOLs.
OCT andaniridia… The zonules are visible in this patient with no iris.
OCT and Iris cyst… The four-scan feature documents the extent and dimensions of an iris cyst
OCT and Iris tumor… On gonioscopy, it is difficult to determine if this iris tumor is in the angle. The Visante OCT confirms it is not and can be used to document if it has grown over time. Also, melanin shows up as a different color on the color map, which allows the tumor to be followed more closely
OCT and iridoschisis This image shows cross-sections of iridoschisis and the associated "shredded" appearance of the iris.
OCT at cataract … The Visante OCT reveals anterior insertion of zonules in this case of lens calcification
OCT at cataract … This image shows both low- and high-resolution images of a hypermature cataract. In the latter, clefts of water are visible inside the lens.
OCT at cataract … • The Visante OCT is useful for evaluating and managing cataract and IOL patients. • The instrument * images the crystalline lens within the pupillary space * measures cataract location and density * defines the anatomical layers of cataract * allows visualization of IOLs in the eye * measures anterior-segment dimensions precisely for placement of phakic IOLs * enables visualization of anterior segment changes due to accommodation . * examination of corneal incision architecture
OCT at cataract … These capabilities are especially helpful for planning challenging cataract cases, providing the surgeon with a better preview of what he or she is facing For example, the instrument clearly images posterior polar opacity, and we are currently determining if we can use that information to precisely predict how posterior polar cataracts and the posterior capsule will act intraoperatively.
OCT and IOL … This image shows imaging and measurement of 7.16° of IOL tilt
OCT and incision … • The Visante OCT has allowed us to rapidly improve our techniques by enabling us to see corneal incision cross-sections and better assess our results. • As a result, deficiencies associated with the "top-hat" approach to penetrating keratoplasty became clear. • The "zigzag" approach seems to be an effective alternative as it resists leakage and doesn't require sutures to be as tight.
OCT and incision … The Visante OCT provides a high-resolution image of the cornea and measurement of its dimensions after a "top-hat" approach to corneal transplant.
OCT and incision … This is a high-resolution postoperative corneal scan of a "zigzag" transplant incision. The angling down, the lamellar cut and angling again are visible.
OCT and angle… • The status of the anterior-chamber angle is highly relevant in the analysis of glaucoma. The Visante OCT provides fast and reliable data for evaluating narrow angles and the risk of closure. It objectively measures or will soon be capable of measuring: • ■ The angle in degrees • ■ Angle opening distance • ■ Angle recess area • ■ Trabeculo-iris space area • ■ Trabeculo-iris contact area.
OCTand angle… A narrow angle is apparent with Visante OCT imaging, in this case 9.5°.
OCTand angle… This image shows an anterior-chamber angle as viewed with gonioscopy and the Visante OCT. The latter replaces subjective evaluation with objective measurement.
OCT and angle… • The system offers an objective view following peripheral iridotomy or iridectomy. • Compared with gonioscopy, the Visante OCT is nontechnical for the practitioner and comfortable for the patient. • It produces minimal light artifact and provides automatic documentation. It doesn't produce pressure artifacts. A significant problem with gonioscopy is the pressure it puts on the cornea. That pressure can open or close the angle.
OCT and angle… An anterior-segment scan shows a patent peripheral Iridectomybut also plateau iris syndrome
OCT and angle… This image shows peripheral anterior synechiae (PAS) on gonioscopy and the Visante OCT.
OCT and angle… Imaging illustrates a very narrow angle and the need for a lensectomy. The lensectomy accomplished the goal of a much more open anatomy.
OCT The Visante OCT is useful for determining if Descemet's-stripping endothelial keratoplastiesare properly attached. This image also shows the inevitable meniscus-shaped cut and a relatively ragged trephine-induced edge
OCT Using the Visante OCT system to monitor “Descemet's-stripping endothelial keratoplasties”, surgeons have learned that the donor tissue typically continues to thin for approximately 3 months, affecting patients' vision. This image also shows the quantification of the donor tissue depth at various points.
OCT OCT Imagesof filter blebs post-trabeculectomy in the right (A) and left (B) eyes of an 89-year-old male. Note the narrow angle in the right eye scan and the large cystic space within the bleb. The wall of the bleb is nicely delineated and evidenced by the anterior-segment optical coherence tomography.
OCT This shallow suprachoroidal effusion, which may or not be seen with ultrasound, is obvious here. Fluid has accumulated in the periphery. The light penetration is not sufficient to pick up the ciliary processes, but the effusion, iris, angle and sclera are clearly visible
A diagnosis of corneal decompensationdue to peripheral tube-corneal touch was made. A surgical revision was performed with tube repositioned more posteriorly.
OCT Figure shows the OCT image with the tube entry site just posterior to the corneal scleral junction (arrow). There is a fibrous membrane (asterix) from the tube to the corneal endothelium that accounts for the opacity seen on slit lamp examination. This effectively ruled out corneal tube contact, and no further surgery was performed.
corneal decompensationdue to peripheral tube-corneal touch was improved by OCT OCT image ruled out corneal tube contact
