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of the anterior segment of the eye Optical Coherence Tomography & Ultrasound BioMicroscopy of the anterior segment of the eye minoo afshar 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

Optical Coherence Tomography “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

OCT

Optical coherence tomography (OCT; Visante by Carl Zeiss Meditec) 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

OCT

OCT

OCT and Cornea …

OCT and ant chamber…

OCT and ant chamber…

OCT and ant chamber…

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.

The zonules are visible in this patient with no iris. OCT and aniridia… 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 Keratometery…

OCT and IOL calculation …

This image shows imaging and measurement of 7.16° of IOL tilt 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 …

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.

OCT and angle…

OCT and angle… A narrow angle is apparent with Visante OCT imaging, in this case 9.5°.

OCT and angle…

OCT and 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 Iridectomy but 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 keratoplasties are 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 Images of 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 decompensation due 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.

OCT image ruled out corneal tube contact corneal decompensation due to peripheral tube-corneal touch was improved by OCT OCT image ruled out corneal tube contact

OCT and LASIK …

OCT and LASIK …

OCT and LASIK …

OCT and PTK …

OCT and PTK …

OCT and PTK …

OCT and PTK …

OCT and PTK …

OCT and PTK …

OCT and PTK …

OCT and KC …

OCT and KC …

OCT and KC …

OCT and KC …

OCT OCT has several theoretical advantages when compared with current imaging modalities for imaging the anterior segment of the eye The system provides clinically useful information related to a long list of pathologies. it is a unique tool that provides us with a wealth of new information that serves to improve patient care. .

OCT and Glaucoma … The system also offers useful tools for planning glaucoma surgery, which is increasingly difficult in light of new approaches and devices. The ability to measure scleral thickness for proper dissections, which the system provides, is important. Postoperatively, the Visante OCT can be used to image scleral and suprachoroidal shunts as well as sub-conjunctival, superchoroidal and superciliary fluid.

OCT Surgeons performing corneal refractive procedures are finding the Visante OCT system an invaluable tool for surgical planning and post-op assessment.

High-frequency Ultrasound BioMicroscopy (UBM) UBM provides high-resolution in vivo imaging of the anterior segment in a noninvasive fashion

UBM The technology for UBM, originally developed by Pavlin, Sherar, and Foster, is based on 50- to 100-MHz transducers incorporated into a B-mode clinical scanner. Higher frequency transducers provide finer resolution of more superficial structures, whereas lower frequency transducers provide greater depth of penetration with less resolution

UBM In addition to the tissues easily seen using conventional methods (ie, slit lamp), such as the cornea, iris, and sclera, by “ UBM ” , structures including the ciliary body and zonules, previously hidden from clinical observation, can be imaged and their morphology assessed

UBM Although UBM cannot distinguish two small objects less than 25 micro m apart along the axial scanning line, it can still measure the distance between two objects far enough apart ( > 25 micro m, such as corneal thickness, anterior chamber depth) with 12-micro m precision.

In the normal eye In the normal eye, the cornea, anterior chamber,posterior chamber, iris, ciliary body, and anterior lens surface can be recognized easily . The scleral spur is the only constant landmark allowing one to interpret UBM images in terms of the morphologic status of the anterior chamber angle and is the key for analyzing angle pathology. The scleral spur is located where the trabecular meshwork meets the interface line between the sclera and ciliary body.

the normal eye Generally, in the normal eye, the iris has a roughly planar configuration with slight anterior bowing, and the anterior chamber angle is wide and clear. Morphologic relationships among the anterior segment structures alter in response to a variety of physiologic stimuli (ie, accommodative targets and light); therefore, maintaining a constant testing environment is critical for cross-sectional and longitudinal comparison.

AOD TIA q 1 TCPD ID1 ID2 ID3 ICPD IZD ILCD ILA q 2 Name UBM Abbreviation Description Angle opening distance AOD Distance between the trabecular meshwork and the iris at 500 mm anterior to the scleral spur Trabecular – iris angle TIA q 1 Angle of the angle recess Trabecular – ciliary process distance TCPD Distance between the trabecular meshwork and the ciliary process at 500 mm anterior to the scleral spur Iris thickness ID1 Iris thickness at 500 mm anterior to the scleral spur ID2 Iris thickness at 2 mm from the iris root ID3 Maximum iris thickness near the pupillary edge Iris– ciliary process ICPD Distance between the iris and the ciliary process along the line of TCPD Iris– zonule distance IZD Distance between the iris and the zonule along the line of TCPD Iris– lens contact distance ILCD Contact distance between the iris and lens Iris– lens angle ILA q 2 Angle between the iris and the lens near the pupillary edge

UBM

UBM and pigment dispersion syndrome … The only type of open-angle glaucoma that shows characteristic findings on UBM is the pigment dispersion syndrome (PDS) . In this familial autosomal dominant disease, mechanical friction between the posterior iris surface and anterior zonular bundles releases iris pigment particles into aqueous flow. These particles are deposited on structures throughout the anterior segment. The diagnostic triad consists of : 1. Krukenberg spindle 2. radial transillumination defects of the midperipheral iris 3. pigment deposition on the trabecular meshwork

…continued Typical UBM findings associated with this condition include : - a widely opened angle - an iris with slight concavity (bowing posteriorly), - increased iridolenticular contact As is true in pupillary block, there is a relative pressure gradient between the anterior and posterior chamber ; however , because the anterior chamber is the one that holds higher pressure, this condition is called ‘‘reverse pupillary block’’ . Laser iridotomy eliminates this pressure gradient, resulting in a flattened iris .

Angle occludability on UBM : Examining eyes with narrow angles requires careful attention to the occludability of the angle. Although provocative testing, such as dark room gonioscopy, is useful for detecting the angle occludability, it is now rarely used, because it is subjective, time consuming, and prone to false negative results owing to the difficulty of standardizing the slit-lamp light intensity. With UBM, dark room provocative testing can be performed in a standardized environment generating objective results by providing information on the state of the angle under normal light conditions and its tendency to occlude spontaneously under dark conditions.

Angle occludability on UBM :

Pupillary block on UBM Pupillary block is the most common type of angle-closure glaucoma. At the iridolenticular contact, resistance to aqueous flow from the posterior to the anterior chamber creates an unbalanced relative pressure gradient between the two chambers , pushing the iris up toward the cornea ( Fig. 3A) . This abnormal resistance causes anterior iris bowing, angle narrowing and acute or chronic angle-closure glaucoma. The other anterior segment structures and their anatomic relationships remain normal. Laser iridectomy equalizes the pressure gradient between the anterior and posterior chambers and flattens the iris. The result is a widened anterior chamber angle (Fig. 3B).

Series of ultrasound biomicroscopy scans covering each quadrant in patient with plateau iris (A–D). Note the shallow anterior chamber and the very narrow angle in all four quadrants. Scans taken before patient underwent a laser peripheral iridotomy followed by an iridoplasty. In plateau iris, the ciliary body is anteriorly placed. The iridotomy addresses the pupillary block component, but not the angle closure related to the abnormal ciliary bodyposition. In such cases, laser iridoplasty is often useful.

UBM and IOL … An intraocular lens is an easy target for UBM visualization, because it is a type of foreign body Optic and haptic locations can be assessed accurately by looking for a strong echo at their interface plane Because the capsular bag cannot always be visualized,the most peripheral portion of the haptic defines its position in the capsular bag, ciliary sulcus, or a dislocated point This technique is used in various studies related to many different types of intraocular lenses

UBM and angle recession … In eyes with angle recession, the ciliary body face is torn at the iris insertion , resulting in a wide-angle appearance with no disruption of the interface in between the sclera and ciliary body …….

(A) UBM and (B) OCT images in angle-recession glaucoma in horizontal plane of left eye in 45-year-old male patient with history of trauma. Note the deeper penetration with ultrasound biomicroscopy, which allows visualization of the posterior lens capsule centrally (arrow).

UBM and cyclodialysis … …In contrast, in cyclodialysis, the ciliary body is detached from its normal location at the scleral spur, creating a direct pathway from the anterior chamber to the supraciliary space (asterix).

UBM In hypotony cases, UBM can distinguish tractional from dehiscence ciliary body detachment, which requires a different management approach.

UBM at Malignant glaucoma… . Malignant glaucoma, also known as ciliary block or aqueous misdirection, presents the greatest diagnostic and treatment challenge . Forces posterior to the lens push the lens–iris diaphragm forward,causing angle closure . UBM clearly shows that all anterior segment structures Are displaced and pressed tightly against the cornea with or without fluid in the supraciliary space (Fig.6).

UBM and Foreign bodies … Foreign bodies generate various artifacts based on their acoustic characteristics In general, materials that contain air (ie, wood and concrete) create shadowing artifact by absorbing most of the incoming ultrasound at their sites A , whereas hard and dense materials (ie, metal and glass) generate comet tail artifacts by reflecting ultrasound back and forth within the materials B .

UBM Ultrasound biomicroscopy is helpful in differentiating solid (B) from cystic (A) lesions of the iris and ciliarybody The size of these lesions can be measured, and the extent to which they invade the iris root and ciliary face can be evaluated. A B

UBM & Plateau iris … A plateau iris configuration occurs owing to a large or anteriorly positioned ciliary body (pars plicata), which pushes the iris root mechanically up against the trabecular meshwork. The iris root may be short and inserted anteriorly on the ciliary face, creating a narrow and crowded angle. The anterior chamber is usually of medium depth, and the iris surface looks flat or slightly convex, just like in a normal eye. With indentation gonioscopy, the ‘‘double-hump’’ sign is observed.

….continued The peripheral hump results from the rigid presence of the ciliary body holding the iris root; the central hump represents the center part of the iris resting over the anterior lens surface. The space between the two humps represents the area between the ciliary processes and the endpoint of iridolenticular contact. These findings can be confirmed by performing indentation UBM, a special technique that imposes mild pressure on the peripheral cornea with the skirt of a plastic eyecup so that one can simulate indentation gonioscopy .

UBM and sutures … Scleral sutures after intraocular surgery can be identified by searching for this shadowing artifact ( by refraction )

OCT vs UBM The Visante OCT system is the first to provide clear, highly detailed, in-depth images of the anterior chamber, including dependable angle information, without the need for ocular anesthesia or a messy, time-consuming water bath. Compared with ultrasound biomicroscopy (UBM), the noncontact OCT instrument is easier to use and acquires images more rapidly. A technician easily can learn to operate the device, including selecting the axis to examine or performing an automatic examination along the four meridians. Each screen and printout specifies right or left eye, and a triangular icon (nose) helps the operator remain oriented. An arrow indicates the direction of the cross-section, and the degree area — e.g., from 0° to 180° — it covers is listed.

The Visante OCT has other advantages over UBM OCT vs UBM The Visante OCT has other advantages over UBM It is wide-field versus narrow-field The patient can be sitting, rather than supine, during imaging. OCT employs light; therefore, it does not require fluid immersion or probe contact But unlike UBM, the current version of the Visante OCT uses 1310-nm light, which is blocked by pigment. However, the nonpigmented opaque ocular structures are permeable, and images can be obtained through a cloudy or white cornea, the conjunctiva and the sclera. OCT has a spatial resolution that easily surpasses that of even ultra high-frequency ultrasound

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