Ultrasound biomicrosopy in glaucoma

ULTRASOUND

BIOMICROSOPY IN

GLAUCOMA

Dr. Aditi Singh

Ultrasound biomicroscope (UBM) is a high

frequency ultrasound machine used to image

ocular structures anterior to the pars plana region of the eye

Provides images of the tissues and structures

in vivo at microscopic resolution

Princess Margaret

Hospital at Toronto,

Canada in 1989.

Dr . Stuart Foster

They developed three probes - 50, 80 & 100 Mhz for

clinical trials .

50 MHz is an ideal compromise between depth and

resolution to visualize the entire anterior segment.

The first commercially available machine was

developed by Zeiss in 1991.

There are three main

components of the

UBM machine.

1.Transducer

2. High-frequency

signal processing.

3. Precise motion

control

This radiofrequency travels the

body tissue and is

reflected back to the transducer.

The reflected

radio frequency is processed by

the signal processing

unit.

Transducer

The signal processing

unit in UBM is specially

designed to handle high

frequency signals.

Subtle movements.

Special motion control

device.

Mounted on a pulley with

the piezoelectric crystal

fixed on a large handle

50 MHz

TechniqueSupine position

Eye is open

Piezoelectric crystal of the

transducer is open

Saline or sterile methylcellulose.

Crystal of the transducer is placed

in saline approximately 2 mm.

from the eye surface

Normal anatomy Lateral resolution - 50µ

Axial resolution - 25µ

Depth of penetration- 4-5 mm.

Field of view is 4 x 4mm

Scan rate is 5 frames/second.

Cornea is the first structure.

Corneo-scleral junction

Quantification of anterior chamber angle

The scleral spur is the most important landmark.

Radio-opaque shadow of the sclera merges with the relatively

radiolucent shadow of the cornea

Trabecular iris angle (TIA) –Angle formed with the

apex at the iris recess and the arms passing through

the TM at a point 500 microns from scleral spur and

the point on iris perpendicularly opposite.

(30±11 degrees)

Iris thickness (ID1) – along the

same line

ID2 – 2 mm from the iris root

ID3 – thickest point near the

pupillary margin

Angle recess area –

triangular area bordered

by the anterior iris

surface corneal

endothelium and a line

perpendicular to the

endothelium drawn to

the iris surface at a point

750 microns from the

scleral spur. Iris

irregularity accounted

for

Evaluation of the anterior chamber angle

in Asian Indian eyes by UBM and

gonioscopy (Kaushik et al) 106 eyes –

narrow angles,57 eyes – open anglesNarrow

angles

Open angles

Mean AOD 250 58±49 176±47

Mean AOD500 102±84 291±62

Mean TCPD 653±124 883±94

Biometry of the Anterior Segment

Corneal thickness

Anterior chamber depth

Posterior chamber depth

IOL thickness

Iris thickness

Ciliary body thickness

Scleral thickness .

Cannot determine lens thickness

Determination of the Mechanism of Primary

Glaucoma

Able to determine the mechanism of elevated IOP

(angle-closure vs open-angle) by showing the

relationship between the peripheral iris and the

trabecular meshwork.

Imaging is possible, even in eyes with corneal

edema or corneal opacification that precludes

gonioscopy.

Open-angle glaucoma

Can measure the anterior chamber angle in

degrees

Assess the configuration of the peripheral iris

Evaluate the iris insertion in relation to the

trabecular meshwork

WIDE OPEN ANGLE WITH FLAT IRIS PLANE

OPEN ANGLE WITH ANTERIORLY BOWED

IRIS PLANE

Determination of the Occludability of the

Angle

Dark room provocative testing

Studies the spontaneous occlusion of the angle

under conditions of decreased illumination

Provides useful qualitative information about

angle recess anatomy.

Indentation UBM

Apposition closure-angle opens on

indentation

Indentation UBM gonioscopy, new method for

assesing the angle

Angles widened with indentation.

The angle changes in eyes with relative pupillary

block were significantly greater than in eyes with

peripheral anterior synechie (PAS) or plateau iris

configuration (PIC).

Useful for diagnosing relative pupillary block, PAS,

and PIC.

Determination of the Mechanism of Secondary

Glaucoma

Pigment Dispersion Syndrome

Wide open angle and typical posterior bowing of

the peripheral iris causing reverse pupillary block

Plateau iris syndrome

Abnormally steep anterior angulation of the peripheral iris.

Anterior insertion of the iris on to the anterior ciliary body.

Can also confirm the double hump sign by use of indentation UBM, a special technique that applies mild pressure on peripheral cornea with the skirt of the eyecup.

Indentation UBM on an eye with a plateau iris

Peripheral anterior synechiae

IRIS BOMBE

Pupillary block(A) The angle shows appositional closure owing to

anterior bowing of the iris.

(B) The angle is open with a flattened iris after laser

peripheral iridotomy.

ANIRIDIA

Iridocorneal endothelial

syndrome

Congenital glaucoma

Common features-

thin stretched out ciliary body,

abnormal tissue at the iridocorneal angle,

abnormal insertion of the ciliary body

In cases of cloudy cornea and unknown previous

glaucoma surgery, UBM can be used to identify

the type and localization of previous surgery in

congenital glaucoma, thus assisting surgical

planning for subsequent management

Post trabeculotomy-remants of tm,iris strands

POST TRAUMATIC GLAUCOMAAngle recession:

Posterior displacement of the point of attachment of the iris to the sclera

Widening of the ciliary body face with no disruption of the interface between the sclera and ciliary body.

Blood in anterior chamber Disinsertion of iris root

Cyclodialysis cleft

Detachment of the

ciliary body from its

normal location at the

scleral spur.

Particularly useful in

the presence of hazy

media, hypotony,

and/or abnormal

anterior segment

anatomy

PSEUDOPHAKIC AND LENS INDUCED

GLAUCOMA

Phacomorphic glaucoma

Glaucoma due to anterior subluxation of lens.

Circumference of intact zonules and the extent of

zonular dialysis in pseudoexfoliation syndrome

In case of intraocular lens (IOL)-induced glaucoma

can clearly delineate the position of the optic and

haptic

especially helpful in pseudophakic bullous

keratopathy in determining the cause of glaucoma

Malignant glaucoma

Extremely shallow anterior chamber

Occluded angle

Forward rotation of the ciliary body with or

without fluid in the suprachoroidal space

Evaluation of Cysts and Tumors Causing Angle

Closure

Internal character of a lesion (solid or cystic)

Resticted anterior ciliary body or is restricted to

the iris

To measure the full extent of the lesion

Progression or regression of the tumor.

Evaluation of glaucoma therapy

Patency of peripheral laser iridotomy

Determining Functional Status of a Filtering Surgery

After trabeculectomy-

Patency of sclerostomy aperture

Patency of peripheral iridectomy

Filtering bleb - flat, shallow, or deep

The grading of the bleb is done according to

intrableb reflectivity, visibility of the route under

the scleral flap, formation of cavernous fluid filled

space, and bleb height.

4 grades :

low reflective (L)

high reflective (H)

encapsulated (E)

flat (F).

Eyes with good IOP control mainly have L type blebs. These have low to moderate intrablebreflectivity, a visible intrascleral route and higher intrableb height. F and E blebs generally denote a surgical failure.

Non-penetrating Deep Sclerectomy

Evaluate the functional status of the surgery

Can evaluate the thickness and demonstrate a non-perforated continuous trabeculum and Descemets membrane.

UBM examination after long-term follow-up shows the presence of an intrascleral space and a filtering bleb. Collagen implants used to augment deep sclerectomy can also be visualized.

Aqueous drainage tubes

UBM is instrumental in diagnosing the presence

and cause of occlusion of aqueous drainage

device

UBM can demonstrate peritubular filtration as a

cause of ocular hypotony after glaucoma shunt

device implant

Evaluation of Postoperative Complications after

Trabeculectomy

UBM can be used to detect and evaluate the extent of

postoperative complications such as ciliochoroidal

effusion and cyclodialysis.

In ciliochoroidal effusion UBM shows the ciliary

body to be edematous and separated from the sclera

by a sonolucent collection of supraciliary fluid

UVEITIC GLAUCOMA

Uveitis, especially pars planitis, is also an

important cause of glaucoma.

Greiner et al used UBM to grade pars

planitis as follows:

grade 0 = no cells

grade 1 = mild cells

grade 2 = marked cells

grade 3 = organization of cells.

EVALUATION OF SUCCESS OF CILIO-

DESTRUCTIVE PROCEDURE

UBM has been used to image early and late

ciliary body alterations after trans scleral

cyclophotocoagulation

to establish the position of the ciliary body to

ensure correct laser probe placement

to locate ciliary body residuals for retreatment,

and to rule out scleral damage after the

procedure.

CONCLUSIONS

An indispensable tool in qualitative and

quantitative assesment of anterior segment.

an excellent view of the pathology occurring in

the anterior and posterior chambers of the eye

and thereby providing a clear insight into the

cause of aqueous obstruction.