Laser Treatment In Glaucoma

Laser Iridotomy

•       relieve pupillary block

•       effective, relatively non-invasive, preferable to surgical iridectomy

Indications for Laser Iridotomy

•       PAC & PACG: if pupillary block significant

•       PACS         

•       Absolute: PAC/PACG in the fellow eye

•       Relative: confirmed family history of PAC/PACG, need for repeated dilated examinations, poor access to regular ophthalmic care, medication required that may provoke pupillary block

•       Secondary angle closure with pupil block e.g. lens induced

•       Not helpful if pupil block not dominant e.g. uveitis, iris cyst and uveal effusion)

Type of laser: Nd:YAG laser, Argon laser, Argon followed by Nd:YAG laser (in thick iris)

Complications: corneal endothelial and/or epithelial burns, endothelial decompensation, IOP spikes, post-laser inflammation, posterior synechia, bleeding, closure of iridotomy hole, cataract formation or progression, glare and monocular diplopia,  retinal burn

 

Laser Iridoplasty

-      Laser burns to contract the peripheral iris in order to widen the anterior chamber angle and access of aqueous humor to angle.

Indications for Laser Iridoplasty

-    Acute

•       Medically unresponsive AAC

•        Patent PI with high IOP or recurrence acute attack

•        Lens induced secondary AAC

•        Contraindication to usual medication

-      Chronic

•       Plateau iris

•       Appositional closure despite patent PI

•       CACG with suboptimal IOP control

Technique: Argon laser 0.2-0.5 sec, 200-500 mW, 500 µm, 30-40 spots/360 degrees

Limitations

•       Developed PAS and IOP rise

•       Trabecular damage

•       Not helpful in PAS

Complications

•       IOP spike

•       Focal corneal endothelial damage

•       Pupil distortion

•       Iritis, pigment dispersion

•       PAS

•       Loss of effect over time

 

Selective Laser Trabeculoplasty (SLT)

            Widely use, relatively effective, non-invasive, avoid medical non adherence, easy to perform

Good Candidates for SLT:

            Suitable for POAG, OHT, NTG, pseudoexfoliation glaucoma, pigmentary glaucoma patients who medical therapy failure or inappropriate, adjunct to medical therapy, primary treatment if appropriate, poor compliance

Mechanism: to enhance TM outflow by frequency-doubled Nd:YAG laser (532 green) aim to cover area of pigment and non pigment TM

Laser Parameters: Spot size 400 micrometer, exposure 3 nanosecond, power 0.4-1.4 mJ, 30-50 spots over 180 degrees

Efficacy:

•        Replace 1 topical medication, decrease IOP 20-30% at 6 months and decrease effect over time to 23% at 6 years (mean survival time 2 years)

•       SLT 180 degrees effectively equal to 360 degrees

•       Procedure can repeat but less efficacy compared to first laser treatment

-      100% of 360 degree SLT and 84% of 180 degree SLT maintain IOP fluctuation of less than 3 mmHg at 2 years

Predictive factors: higher baseline IOP related with higher success rate

 

Endoscopic Cyclophotocoagulation (ECP)

Microglaucoma surgery

Instrument:

•       probe is key point – have both light source (175 W xenon for illumination) and aiming beam (helium-neon laser)

•       810 nm diode laser

Approach: anterior (clear cornea) or posterior (pars plana)

Anaesthesia: subtenon or retrobulbar block

Patient Selection:

•       Stand alone: aphakic or pseudophakic

•       Combined with cataract Sx

•       Combined with other surgeries

Special cautions:

•       Localized zonule weakness or dialysis

•       Advanced PXG: limited laser uptake

•       Uveitis or NVG : not contraindicate but beware of severe inflammation or post-op hypotony

•       Phakic: beware of capsular damage

Complications: minimal

1.      Inflammation

2.      IOP spike

3.      Cataract progression: easily

 

Cyclophotocoagulation with MicroPulse Technology

new alternate laser to the standard diode transcleral cyclophotocoagulation (G probe).

Concept: continuous wave mode to minimize thermal elevation reduce energy, different pathway of decrease IOP

Instrument: Irides Cyclo G6 MP laser (810 nm)

FDA approved in USA in early 2016

Pros

•       Griddle, gentle slightly move on conjunctiva

•       Not necessary to use eyelid speculum

•       Minimise collateral thermal damage

•       No evidence of structure change

•       Effect on the 1st day to 1 week (less inflammation)

•       40% IOP reduction

•       Reduction of inflammation and phthisis (complications in Diode probe)      

           

Laser treatment in angle closure glaucoma: laser iridotomy? or laser iridoplasty?

•       Diagnosis and pathology are the keys of choosing laser strategy.

•       Appropriate laser treatment should be done before irreversible change of both TM and optic nerve head.

•       Laser iridotomy: definitive treatment of PAC with pupillary block, but remaining progressive narrowing of angle.

•       Laser iridoplasty:

•       Alternative approach for acute PAC (effective result)

•       Eliminate residual appositional closure (plateau iris)

•       As routine treatment: unproven

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