Lasers in Glaucoma Presenter: Dr. David Luellwitz Introducon • A laser is a device that emits light through a process of op<cal amplificaon based on the smulated emission of electromagne<c radiaon. • Proper<es of laser • Monochromac • Coherent • Parallelism • Brightness Lasers used in glaucoma 488 - 514 nm - Argon blue-green & green 810 nm Diode 1064 nm - Nd:YAG 10,600 nm - Carbon dioxide Different types of laser LASERS Gas Solid State Metal EXCIMER Dye Diode Vapour Argon Ruby Copper Argon Fluoride Krypton Nd Yag Gold Helium Neon Carbon Dioxide Three basic light-ssue interacons • Photocoagulaon • Laser light is absorbed by the target <ssue or by neighboring <ssue, generang heat that denatures proteins (i.e., coagulaon) • Photodisrup<on • Power density is so great that molecules are broken apart into their component ions, creang a rapidly expanding ion ‘plasma.’ This ionizaon and expanding plasma create subsequent shock-wave effects which cause an explosive disrup<on of <ssue to create an excision • Photoablaon: • breaks the chemical bonds that hold <ssue together, essen<ally vaporizing the <ssue Modes of operaon Con<nuous Wave (CW) Laser: It delivers the energy in a con<nuous stream of photons. Pulsed Lasers: Produce energy pulses of a few micro to milliseconds. Q Switched Lasers: Deliver energy pulses of extremely short duraon (nanosecond). Mode-locked Lasers: Emits a train of short duraon pulses (picoseconds to femtoseconds) Lasers in Open angle glaucoma • OuTlow enhancement • Laser trabeculoplasty • Inflow reduc<on • Cyclophotocoagulaon(for end stage disease) Lasers in Angle closure glaucoma • Relief of pupillary block • Laser iridotomy • Modificaon of iris contour • Laser iridoplasty • Inflow reduc<on • Cyclophotocoagulaon(end stage disease) Lasers in Post-opera3ve treatment • Laser suture lysis • Adjacent to trabeculectomy • Laser sclerostomy • Laser gonio-puncture • Adjacent to non-penetrang surgery Nd:YAG laser • Beckman and Sugar in 1973 were first to use Nd:YAG laser • Neodymium crystal is embedded in y_rium-aluminium garnet • It can be operated in • Free mode • Q-switched • Mode locked regime • Free mode has thermal effect on <ssue • While Q-switched and mode locked have photo disrup<ve effect. • Q-switched and mode locked regime • truly pulsed lasers with emissions of high power density in very short duraon. • Q-switched system • energy within the laser cavity is raised several <mes by making the usually par<ally reflec<ve mirror totally opaque. • Then suddenly making it transparent again by using polaroid filters • So there is rapid deple<on of energy confined within laser cavity. Q-switched Mode lock Duraon 10-20ns 30-70ns Irradiance 106 109 Op<cal switching Pockel cell/dye Dye Efficiency Beer Poor •In pockel cell - op<cal switching occurred by electrical modulaon •While in dye - op<cal switching occurs when the energy buildup becomes very high •So dye driven switches are inefficient and prone to malfunc<oning. Laser iridotomy • Laser treatment to connect anterior and posterior chamber to relieve pupillary block. • Effec<ve for pupillary block • Relavely non invasive • Preferable to surgical iridotomy indicaon • Definive indicaons • Acute angle closure. • Chronic (creeping) angle closure • Mixed mechanism glaucoma • Phacomorphic with an element of pupillary block • Iris bombé • Rela3ve indica3ons • Cri<cally narrow angles in asymptomac paents • Younger paents, especially those who live some distance from medical care or who travel frequently • Narrow angles with posi<ve provocave test • Iris–trabecular contact demonstrated by compression gonioscopy Types of laser • Photodisrup<ve Nd:YAG laser,(Q-switched and mode-lock) • The photothermal argon lasers Pa3ent prepara3on • Pilocarpine 1% is ins<lled twice, 5 minutes apart; miosis helps to stretch and thin the iris. • Proparacaine 0.5% drops are ins<lled immediately before the procedure Lens choice • Abraham lens- 66D planoconvex buon. • The Wise lens -103D planoconvex buon, • concentrates the laser energy more • it minimizes the spot and magnifies the target even more • difficult to focus. • Advantage of the Abraham lens -energy delivered to both cornea and re<na is four <mes less than that with Wise lens. Specific techniques • Place- peripheral iris under the upper eyelid to avoid ghost images that may arise through the iris hole. • Iris crypts represent thinner iris segments and, as such, are penetrated more easily. • The superonasal posi<on (at 11 and 1 o’clock) is the best posi<on to use to prevent inadvertent irradiaon of the fovea Laser Iridotomy - posion Nd-YAG laser • The energy- 3–8 mJ, • Pulses- there are 1–3 per shot, and one or more shots are used for penetraon • The Q-switched mode is used • Place-between the 11 and 1 o’clock posi<ons, • Iris blood vessels are avoided Argon laser • Long pulses (0.2 seconds) for light-colored irides (blue, hazel, light brown), • short pulses (0.02–0.05 seconds) for dark brown irides. • Power; 1000 mW • Spot size ; 50 μm • single area is treated with superimposed applicaons un<l perforaon is obtained • pigment flume is found to move forward (“smoke sign” or “waterfall sign”) Del Priore L.V., Robin A.L., Pollack I.P.: Neodymium:YAG and argon laser iridectomy: long term follow-up in a prospec<ve randomized clinical trial. Ophthalmology 1988; 95:1207-1211 Post laser management • Steroids are given 4 <mes a day for 7 days to reduce post laser inflammaon . • An<-glaucoma medicaon like B-blockers are given 2 <mes a day for 7 days to reduce chances of post laser IOP spike. • Paent is re-checked aer 7 days for IOP and patency of iridotomy. Argon versus Nd:YAG Laser Argon laser Nd:YAG laser • . Uptake of energy Require pigmented cells Doesn’t require Iris colour Dark brown Light and medium colour iris Late closure High chance Less chance Combined Argon Nd:YAG technique • Used in sequen<al combinaon for dark brown irides or for paents who are on chronic an<coagulant therapy • First, the argon laser (short-pulse mode) is used to aenuate the iris to about one fourth the original thickness and to coagulate vessels in the area. • Then Nd:YAG laser is used, with the beam focused at the center of the crater; one or more bursts are used to complete the iridectomy. Complica3ons • Intraocular Pressure Spikes • Laser-Induced Inflammaon • Iridectomy Failure • Diplopia • Bleeding • Lens Opaci<es • Corneal Injury Laser peripheral iridoplasty • It is an effec<ve means of opening an apposi<onally closed angle. • Procedure consists of placing contrac<on burns in the extreme periphery to contract the iris stroma between the site of burn and the angle so it physically opens an angle. • Argon laser are used with the lowest power seng that creates contrac<on of the iris Laser Iridoplasty Note the almost Ring like burns for laser iridoplasty • Spot size : 100–200- µm • Power: 100–30o mW • Duraon : 0.1 second. • Lighter irides will require slightly higher energy levels than darker • Ten to twenty spots evenly distributed over 360º of the iris are usually sufficient Indicaon • A_ack of angle closure glaucoma • Plateau iris syndrome commonest indicaon • Angle closure related to size or posi<on of lens • Nanophthalmos • Facilitate access to the trabecular meshwork for laser trabeculoplasty • Minimize the risk of endothelial damage during iridotomy Contraindica3ons • Contraindicaon • Advanced corneal edema or opacificaon • Flat anterior chamber • Synechial angle closure • Complicaon: • mild iris • Corneal endothelial burn • Transient rise in IOP Laser trabeculoplasty • Relavely effecve,non-invasive. • Laser treatment to trabecular meshwork increase to increase oulow. Mechanism of ac3on • Wise and Wi_er proposed that thermal energy produced by absorp<on of laser by pigmented trabecular meshwork caused shrinkage of collagen of trabecular lamellae this opened up intertrabecular space in untreated region and expanded schlemm’s canal by pulling the meshwork centrally • Eliminaon of some trabecular cells pos_rbeculoplasty.this s<mulate remaining cells to produce different composi<on of extracellular matrix with lesser ouTlow obstruc<ng proper<es. Laser trabeculoplasty • Method • Argon laser trabeculoplasty • Selec<ve laser trabeculoplasty • Lens • Goldmann 3 mirror lens • Lana trabeculoplasty lens: Argon laser trabeculoplasty • Laser parameter • Power -300-1200mW • Spot size—50µm • Duraon -0.1 sec • Number of burns-30-50 spots evenly placed over 180deg. remaining in subsequent visit. Argon laser trabeculoplasty • Ideally,spot should be applied Over schlemm’s canal avoding The iris root at the junc<on of Anterior 1/3 to posterior 2/3 of Meshwork. • The energy level should be set To induce a reac<on from a Slight transient blanching of The treated area to small Bubble formaon Selecve laser trabeculoplasty • SLT target pigmented trabecular meshwork cells without causing thermal damage to non-pigmented cells or structure. • Laser :Frequency doubled Q switched ND:YAG laser • Pulse :3nsec. • Spot size 400 µm • Power :o.8 mJ power • No.of spots :apprx.50 spots are applied • End point :minimal bubble or no bubble Selecve laser trabeculoplasty (arrow) versus argon laser trabeculoplasty treatment (arrowhead). (Courtesy of M. Berlin, MD.) Comparison ALT SLT TYPE OF LASER Argon blue green 488/514nm Double frequency Nd:YAG 532nm Spot size(µm) 50 400 Duraon 0.1s 3ns Power 300–900 mW 0.6–1.2 mJ Degrees 180 180–360 Indicaons • Chronic open angle glaucoma • Exfoliaon syndrome • Pigmentary glaucoma • Glaucoma in aphakia or pseudophakia Contraindica3ons • Closed or extremely narrow angles • Corneal