نام بهخداوند بخشنده ومهربان

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

Tomography means cross-sectional imaging

“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

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

LASIKIntacsCorneal Scar & PTKBiometry for Phakic IOLCorneal Power & IOL Power CalculationKeratoconusTear MeniscusNarrow Angle Glaucoma

OCTThe Visante OCT system has many clinically

practical uses for the anterior-segment surgeon, including:

Angle assessment Pachymetry Glaucoma surgery evaluation Evaluation of corneal transplantVisualization of the sclera,suprachoroidal

space Identification of iris lesionsEvaluation of crystalline lens,

pseudophakic IOLs.

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 …

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.

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

UBMAlthough 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.

Name UBM

Abbreviation

Description

Angle openingdistance

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

Iris thickness ID2 Iris thickness at 2 mm from theiris root

Iris thickness ID3 Maximum iris thickness near the pupillary edge

Iris– ciliary processdistance

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 .

UBMUltrasound 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.

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

Thank you