Jagdish Dukre

Introduction

In 1961, Zweng and Flocks introduced the concept of applying light energy to the anterior chamber angle for the treatment of glaucoma.

In 1979, Wise and Witter described the first successful protocol of what has become known as laser trabeculoplasty

1979 Argon Laser [488 nm blue-green, 514 nm green]

1984 Krypton Laser [red 647.1 nm, yellow 568.2 nm]

1988 Nd:YAG Laser [1064 nm]

1990 Diode Laser [810 nm]

1996 Solid State “ALT” [532 nm]

2001 Frequency Doubled Nd:YAG laser: SLT [532 nm]

2006 Diode MicroPulse Laser: MLT [810 nm]

2008 Titanium:Sapphire Laser [790 nm]

Indications

when IOP remains above "target" IOP despite maximally tolerated medical therapy

when patients are noncompliant

pseudoexfoliation glaucoma

when surgery needs to be deferred due to a patient's systemic status

Contraindications

Narrow angles

Presence of peripheral anterior synechiae

Uveitis

Advanced glaucoma

Developmental glaucomas.

Mechanical theory

Biologic theory

Cell division theory

Theories Of Mechanism

thermal energy produced by

pigment absorption

shrinkage of collagen in the

trabecular lamellae

shortening of the treated meshwork

enlarge existing spaces between

two treatment sites

Mechanical theory

Biologic Theory

Laser energy causes tissue injury with a resultant cascade of events.

Upregulation of interleukin I and tumor necrosis factor also upregulates metalloproteinase expression.

Macrophages are attracted, and they alter the secreted extracellular matrix, allowing an increased aqueous outflow.

Cell Division Theory

Laser applications stimulate cell division in the anterior TM.

Loss of endothelial cells over the trabecular beams causes the peripheral corneal endothelial cells to divide and slide over the lasered areas.

These cells produce different extracellular matrix, enhancing the aqueous outflow.

Preoperative Preparation

Patients are instructed to continue all glaucoma medications on their regular schedule.

Patients are routinely pretreated with apraclonidine to prevent a significant IOP spike that could adversely affect visual function.

The eye should not be exposed to diagnostic procedures before the treatment because this can affect corneal clarity.

Surgical Technique

Argon laser trabeculoplasty is performed using topical anesthesia.

The gonioscopic mirror of an antireflection-coated, three-mirror lens is used routinely.

Ritch trabeculoplasty lens.

A 17-diopter planoconvexbutton lens over two mirrors provides 1.4 magnification, reducing a 50-µm laser spot to 35 µm

Before starting treatment, it is critical to identify the angle landmarks.

The treatment begins with the gonioscopic mirror at the 12 o'clock position viewing the inferior angle.

The inferior angle tends to be the most open part and has the most pigmentation, making angle structures more clearly defined in this area.

This facilitates identification of the angle landmarks and avoids treating the wrong part of the angle.

The use of a fixation light for the contralateral eye assists the patient in maintaining the appropriate eye position.

Before the initiation of treatment, the eyepieces are focused and the argon laser is set to the standard treatment parameters: a spot size of 50 μm, a duration of 0.1 seconds, and an average power of 800 mW (range 600 to 950 mW).

During the treatment, the power setting required to blanch the trabecular meshwork or cause a small bubble formation is empirically determined.

It is helpful to use a standardized treatment technique. This involves starting with the mirror at the 12 o'clock position and rotating it in a clockwise manner.

The laser burns are placed at the anterior border of the pigmented trabecular meshwork.

The more posterior the treatment, the greater the incidence of IOP elevation and formation of posterior synechiae.

The aiming beam should be the smallest and roundest target possible.

This can be achieved by mechanically directing the laser beam forward and backward.

If the treating contact lens is tilted and not perpendicular to the eye, the aiming beam will appear oval.

the lens on the eye and making sure that the aiming beam is perpendicular to the lens ensures that the full power density of the treatment will be achieved.

If the trabecular meshwork cannot be seen easily, having the patient move the eye in the direction of the gonioscopic mirror often opens the angle and improves visibility.

The spacing of the laser burns is the same whether 180°or 360° are treated, that is, 20 to 25 burns per 90° of angle treated, regardless of the area treated.

POSTOPERATIVE

MANAGEMENT

The patient is instructed to continue all glaucoma medications as usual and begin a topical steroid drop four times a day for 4 to 5 days.

If the patient has had a significant IOP elevation or has severe glaucomatous damage, the IOP is measured the next day.

Most patients are reexamined 2 to 5 days later and then at about 4 weeks.

If at 4 weeks the pretreatment goal has not been achieved, the second half of the angle can be treated.

Complications

Transient IOP elevation

Iritis

peripheral anterior synechiae

membrane covering the entire trabecular

meshwork

Transient IOP elevation

the pressure rise is mild and lasts less than 24 hours

IOP rise occurs within 2 hours after treatment in most cases

IOP rise occurs within 2 hours after treatment in most cases

mechanism of posttrabeculoplasty pressure rise is an inflammatory reaction, with fibrinous material and tissue debris in the meshwork

Iritis common early posttrabeculoplasty complication

49% eyes showed significant inflammation

inflammation peaked 2 days after the treatment

More frequent in eyes with exfoliation syndrome or pigmentary glaucoma

It is mild and transient and easily controlled with a brief postoperative course of topical corticosteroids

postoperative management includes prednisolone 1%, or fluorometholone 0.1%, four times daily for 5 days

Peripheral Anterior

Synechiae The formation of peripheral anterior synechiae is

also a common complication of trabeculoplasty.

These are typically small and tented, corresponding to the location of the laser applications.

Membrane most serious late posttrabeculoplasty complication

Histopathologic studies show changes in the trabecular meshwork, including an endothelial layer over the inner surface

It can lead to an increase in resistance to aqueous outflow.

It is more common in eyes in which a higher number of trabeculoplasties was performed

Selective Laser Trabeculoplasty

frequency-doubled Q-switched 532-nm Nd:YAG laser.

repeatable procedure because of the lack of coagulation damage to the trabecular meshwork.

A total of approximately 50 to 60 adjacent, nonoverlapping spots are placed over 180 degrees of the trabecular meshwork with energy ranging from 0.5 to 1.2 mJ per pulse, set to prevent bubble formation

A Latina lens, Goldmann 3 mirror or Ritch lens is used for he procedure

The aim is to cover the angle, but taking care that the laser spot should not impinge upon the iris

3 nanoseconds (preset); Spot Size: 400 microns (preset); Energy: 1.0 mJ/pulse

It targets the melanocytes in the trabecular meshwork.

The biologic response in the trabecular meshwork results in release of cytokines that trigger macrophage recruitment.

This in turn causes IOP reduction by increased aqueous outflow through the TM.

SLT treats the meshwork without causing any thermal or coagulative damage to the surrounding structures

TITANIUM:SAPPHIRE LASERTRABECULOPLASTY

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