lasers in glaucoma
DESCRIPTION
Lasers in Glaucoma, Dr.Parth Satani, Dr.Rita Dhamankar, Laxmi Eye InstituteTRANSCRIPT
Lasers in Glaucoma
Presenter:Dr.Parth Satani
Moderator:Dr.Rita Dhamankar
Introduction
A laser is a device that emits light through a process of opticalamplification based on the stimulated
emission of electromagnetic radiation.
Properties of laser
Monochromatic
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
Carbon Dioxide
Neon
Helium
Krypton
Argon
Gas
Nd Yag
Ruby
Solid State
Gold
Copper
Metal
Vapour
Argon Fluoride
EXCIMER Dye Diode
LASERS
Three basic light-tissue interactions Photocoagulation
Laser light is absorbed by the target tissue or by neighboring tissue, generating heat that denatures proteins (i.e., coagulation)
Photodisruption
Power density is so great that molecules are broken apart into their component ions, creating a rapidly expanding ion ‘plasma.’ This ionization and expanding plasma create subsequent shock-wave effects which cause an explosive disruption of tissue to create an excision
Photoablation:
breaks the chemical bonds that hold tissue together, essentially vaporizing the tissue
Modes of operation
Continuous Wave (CW) Laser: It delivers the energy in a continuousstream of photons.
Pulsed Lasers: Produce energy pulses of a few micro to milliseconds.
Q Switched Lasers: Deliver energy pulses of extremely short duration(nanosecond).
Mode-locked Lasers: Emits a train of short duration pulses(picoseconds to femtoseconds)
Lasers in Open angle glaucoma
Outflow enhancement
Laser trabeculoplasty
Inflow reduction
Cyclophotocoagulation(for end stage disease)
Lasers in Angle closure glaucoma
Relief of pupillary block
Laser iridotomy
Modification of iris contour
Laser iridoplasty
Inflow reduction
Cyclophotocoagulation(end stage disease)
Lasers in Post-operative treatment
Laser suture lysis
Adjacent to trabeculectomy
Laser sclerostomy
Laser gonio-puncture
Adjacent to non-penetrating surgery
Nd:YAG laser
Beckman and Sugar in 1973 were first to use Nd:YAG laser
Neodymium crystal is embedded in yttrium-aluminium garnet
It can be operated in
Free mode
Q-switched
Mode locked regime
Free mode has thermal effect on tissue
While Q-switched and mode locked have photo disruptive effect.
Q-switched and mode locked regime truly pulsed lasers with emissions of high power density in very
short duration.
Q-switched system
energy within the laser cavity is raised several times by making the usually partially reflective mirror totally opaque.
Then suddenly making it transparent again by using polaroidfilters
So there is rapid depletion of energy confined within laser cavity.
Q-switched Mode lock
Duration 10-20ns 30-70ns
Irradiance 106 109
Optical switching Pockel cell/dye Dye
Efficiency Better Poor
•In pockel cell - optical switching occurred by electrical modulation•While in dye - optical switching occurs when the energy buildup becomes very high •So dye driven switches are inefficient and prone to malfunctioning.
Laser iridotomy
Laser treatment to connect anterior and posterior chamber to relieve pupillary block.
Effective for pupillary block
Relatively non invasive
Preferable to surgical iridotomy
indication
Definitive indications
Acute angle closure.
Chronic (creeping) angle closure
Mixed mechanism glaucoma
Phacomorphic with an element of pupillary block
Iris bombé
Relative indications
Critically narrow angles in asymptomatic patients
Younger patients, especially those who live some distance from medical care or who travel frequently
Narrow angles with positive provocative test
Iris–trabecular contact demonstrated by compression gonioscopy
Types of laser
Photodisruptive Nd:YAG laser,(Q-switched and mode-lock)
The photothermal argon lasers
Patient preparation
Pilocarpine 1% is instilled twice, 5 minutes apart; miosis helps to stretch and thin the iris.
Proparacaine 0.5% drops are instilled immediately before the procedure
Lens choice
Abraham lens- 66D planoconvex button.
The Wise lens -103D planoconvex button,
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 retina is four times 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 position (at 11 and 1 o’clock) is the best position to use to prevent inadvertent irradiation of the fovea
Laser Iridotomy - position
Nd-YAG laser
The energy- 3–8 mJ,
Pulses- there are 1–3 per shot, and one or more shots are used for penetration
The Q-switched mode is used
Place-between the 11 and 1 o’clock positions,
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 applications until perforation 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 prospective randomized clinical trial. Ophthalmology 1988; 95:1207-1211
Post laser management
Steroids are given 4 times a day for 7 days to reduce post laser inflammation .
Anti-glaucoma medication like B-blockers are given 2 times a day for 7 days to reduce chances of post laser IOP spike.
Patient is re-checked after 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 sequential combination for dark brown irides or for
patients who are on chronic anticoagulant therapy
First, the argon laser (short-pulse mode) is used to attenuate 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.
Complications
Intraocular Pressure Spikes
Laser-Induced Inflammation
Iridectomy Failure
Diplopia
Bleeding
Lens Opacities
Corneal Injury
Laser peripheral iridoplasty
It is an effective means of opening an appositionally closed angle.
Procedure consists of placing contraction 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 setting that creates contraction of the iris
Laser Iridoplasty
Note the almost Ring like burns for laser iridoplasty
Spot size : 100–200- µm
Power: 100–30o mW
Duration : 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
Indication
Attack of angle closure glaucoma
Plateau iris syndrome commonest indication
Angle closure related to size or position of lens
Nanophthalmos
Facilitate access to the trabecular meshwork for laser trabeculoplasty
Minimize the risk of endothelial damage during iridotomy
Contraindications
Contraindication
Advanced corneal edema or opacification
Flat anterior chamber
Synechial angle closure
Complication:
mild iritis
Corneal endothelial burn
Transient rise in IOP
Laser trabeculoplasty
Relatively effective,non-invasive.
Laser treatment to trabecular meshwork increase to increase outflow.
Mechanism of action
Wise and Witter proposed that thermal energy produced by absorption 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
Elimination of some trabecular cells posttrbeculoplasty.thisstimulate remaining cells to produce different composition of extracellular matrix with lesser outflow obstructing properties.
Laser trabeculoplasty
Method
Argon laser trabeculoplasty
Selective laser trabeculoplasty
Lens Goldmann 3 mirror lens
Latina trabeculoplasty lens:
Argon laser trabeculoplasty
Laser parameter Power -300-1200mW
Spot size—50µm
Duration -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 junction of
Anterior 1/3 to posterior 2/3 of
Meshwork.
The energy level should be set
To induce a reaction from a
Slight transient blanching of
The treated area to small
Bubble formation
Selective 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
Selective 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 frequencyNd:YAG 532nm
Spot size(µm) 50 400
Duration 0.1s 3ns
Power 300–900 mW 0.6–1.2 mJ
Degrees 180 180–360
Indications
Chronic open angle glaucoma
Exfoliation syndrome
Pigmentary glaucoma
Glaucoma in aphakia or pseudophakia
Contraindications
Closed or extremely narrow angles
Corneal edema
Aphakia with vitreous in ant.chamber
Vascular glaucoma
Acute uveitis
Primary congenital glaucoma
Angle recession glaucoma
Complications
Most common risk is IOP spikes in about 3–5% of patients
Iritis
Peripheral ant.synechiae
Hemorrhage
Corneal complication
Waning of response
Comparison
ALT maintained IOP control in 67–80% of eyes for 1 year, in 35–50% for 5 years, and in 5–30% for 10 years (i.e., an attrition rate of 6–10% per year).
With SLT, IOP lowering occurs within 1–2 weeks; IOP lowering can continue for up to 4–6 months post-treatment and also continues for 3–5 years with a similar attrition to ALT
Shingleton B.J., Richter C.U., Belcher C.D., et al: Long-term efficacy of argon laser trabeculoplasty. Ophthalmology 1987; 94:1513-1518
Weinand F.S., Althen F.: Long-term clinical results of selective laser trabeculoplasty in the treatment of primary open angle glaucoma. Eur J Ophthalmol 2006; 16:100-104.
Lasers in malignant glaucoma
Argon laser
Power :200–800 mW
Duration :0.1 second
spot size :100–200- µm.
This may restore the normal forward flow of aqueous, especially when accompanied by aggressive cycloplegic, mydriatic, and hyperosmotic therapy
The Nd:YAG beam is directed at the anterior hyaloid face between the ciliary processes using a single burst at power
settings used for posterior capsulotomy.
In aphakic ciliary block glaucoma the Nd:YAG laser can rupture the vitreous face and break the block.
Pseudophakic ciliary block glaucoma can also be treated with a Nd:YAG laser by rupturing anterior hyaloid .
Rupture of the posterior capsule may be needed to break the block in some cases
Cyclophotocoagulation
Reduce aqueous production by destruction of ciliaryepithelium
Techniques Transscleral
Transpupillary
Endolaser
Indication Failure of multiple filtering surgeries
Primary procedure to alleviate pain in neovascular glaucoma with poor visual potential.
Painful blind eye
Surgery not appropriate
Cyclophotocoagulation
Trans-scleral cyclophotocoagulation
destroys ciliary epithelium and associated vasculature
decreased aqueous humor production.
Nd:YAG laser –
good scleral penetration
light energy is absorbed by blood and pigment of the ciliary body.
Diode laser (810 nm) has lower scleral transmission than the Nd:YAG laser (1064 nm) but greater absorption by melanin.
So use of 50% less energy compared to the continuous wave Nd:YAG laser to achieve the same effect
Cyclophotocoagulation
Trans-scleral Cyclophotocoagulation
Noncontact Nd:YAG laser cyclophotocoagulation
Contact Nd:YAG laser cyclophotocoagulation
Semiconductor diode laser trans-scleral cyclophotocoagulation
Endoscopic cyclophotocoagulation
Cyclophotocoagulation
Noncontact Nd:YAG laser cyclophotocoagulation Nd:YAG laser is mounted on slit-lamp
4–8 J/pulse,
duration :20 ms
placed 1.0–1.5 mm posterior to the limbus total of 30–40 spots
3 and 9 o’clock positions spared to avoid long posterior ciliaryarteries
A contact lens may be used to blanch blood vessels to improve the focus
Atropine 1% and prednisolone acetate 1% are prescribed four times a day; these are tapered as inflammation subsides.
Cyclophotocoagulation
Contact Nd:YAG laser cyclophotocoagulation Nd:YAG laser in the continuous mode via a fiber optic system in
direct contact with the conjunctiva
The fiber optic laser probe is positioned perpendicularly on the conjunctiva with the anterior edge 0.5–1.0 mm posterior to the surgical limbus.
power level of 4–9 W and duration between 0.5 and 0.7 seconds
Cyclophotocoagulation
Semiconductor diode laser trans-scleralcyclophotocoagulation
most widely used method of ciliary ablation with reported success rates ranging from 40% to 80%.
it is semiconductor diode laser (wavelength 810 nm)
1500–2500 mW for 1.5–3 seconds and a total of 18–24 spots
ENDOSCOPIC LASER CYCLOPHOTOCOAGULATION
ENDOSCOPIC LASER CYCLOPHOTOCOAGULATION Performed with an 810 nm diode laser
Xenon light source that provides illumination and a helium-neon laser aiming beam
starting settings are 0.25 W with continuous exposure time.
The actual time of exposure is based on visual effect of ciliaryprocess shrinkage and whitening
Typically, as much of the ciliary process is treated as possible, as there is a significant portion posteriorly that is usually not treated
cycloplegics are not necessary and steroids are used in the usual postoperative dosing
Comparison
Complications
Conjunctival burn
Hyphema
Inflammation
Pain
IOP spike
Cataract
Pupil abnormality
Hypotony
Need for re-treatment
Loss of visual acuity
Vitreous hemorrhage
Choroidal detachment
Phthisis
CO2 Laser Assisted SclerectomySurgery Similar to trabeculectomy
Major difference being that after the scleral flap is raised, the remaining sclera over the Schlemm’s canal and trabecularmeshwork is dissected by the CO2 laser probe until aqueous percolated over the entire dissected bed.
Aimed to prevent intra ocular complications.
Performed under sub-conjunctival anesthesia.
CO2 Laser Assisted SclerectomySurgery
Drawbacks
Demands careful and delicate surgery
Relatively long learning curve
Can be performed only by highly skilled surgeons,
Laser suture lysis
Subconjunctival trabeculectomy flap sutures can be lysed with the laser postoperatively if there is inadequate filtration
Dark nylon or proline sutures can usually be severed with the argon laser
settings of 200–1000 mW for 0.02–0.15 second with a 50–100-µm spot size
feasible from about 3–15 days after surgery or up to at least 2 months or more after mitomycin-C use
Singh J, et al: Enhancement of post trabeculectome bleb formation by laser suture lysis, Br J Ophthalmol80:624, 1996.
Method
Laser suture lens. The device has a small convex lens that compresses the edematous conjunctiva permitting a clear view of the tiny nylon suture underneath the conjunctiva. This suture then can be cut easily with a 50-µm spot laser beam using 400 mW of energy for 0.1 second.(Photo courtesy of John Hetherington Jr, MD, University of California,San Francisco.)
Dense hemorrhage in the tissues overlying the suture will absorb the energy, prevent treatment, and possibly cause conjunctival perforation.
fluorescein-stained conjunctiva limits argon laser energy transmission to the sutures and may cause conjunctival
perforation.
thick, inflamed Tenon’s capsule may also preclude successful LSL
After laser steroid is given to reduce external scarring
Additional suture can be lysed 1-2 days after
Reopening of failed filtration site Filtering sites can close because of fibrosis on the external side
Membrane formation or iris incarceration on the internal side of the sclerostomy
Argon or Q-switched Nd:YAG laser can vaporize it With the argon laser, settings of 300–1000 mW at 0.1–0.2 second with a 50–100-µm spot
The Nd:YAG laser is also useful in opening an obstructed sclerostomy
Single bursts of 2–4 mJ are delivered via a Nd:YAG coated goniolens to disrupt any translucent membrane obstructing it.
Kandarakis A, et al: Reopening of failed trabeculectomies with ab interno Nd:YAG laser, Eur J Ophthalmol 6:143,
1996.
Femto laser in the offing
Applications for the femto laser ab externo include
Creating trabeculectomy flaps,
Non-penetrating procedure flaps,
Near-perforating deep excisions under flaps,
Removal or thinning of trabecular meshwork and the inner wall of Schlemm’s canal, and creating suprachoroidal fistulae
Excimer Laser
ab interno procedures include
ELT (excimer laser trabeculostomy) equivalent using docked gonio lens delivery systems
To Create full thickness or near full thickness scleralwindows for trabeculectomy
To create suprachoroidal fistulae.
Cyclodialysis and laser
Cyclodialysis clefts have been both opened and closed with laser
Argon laser photocoagulation using thermal burns of 0.1 second 100-µm spot size, and 500 mW can be used to close cyclodialysisclefts and reduce hypotony
Nd:YAG is used to open cleft.
Closure of a cyclodialysis cleft. The beam is aimed deep into the cleft to create an inflammatory response and generate closure.Postoperative mydriasis and cycloplegia may aid this process.
Laser synechiolysis
The argon laser can be used to pull early or lightly adherent
peripheral anterior synechiae away from the angle or cornea.
(400–800 mW, 0.1–0.2 second,50–100-µm spot size
It is simillar to iridoplasty
Helpful to break and arrest formation of iridocorneal adhesions after penetrating keratoplasty or other forms of peripheral anterior synechiae.
Chronic synechiae can be very resistant to argon iridoplasty.
The Nd:YAG laser can lyse iris adhesion.
Use- early irido–corneal–endothelial (ICE) syndrome to disrupt synechiae,
Side-effect is bleeding.
Goniophotocoagulation
Use - anterior segment neovascularization
Goniophotocoagulation is useful to obliterate fragile vessels in a surgical wound like in cataract incisions or trabeculectomy or goniotomy wounds
Argon laser 100-µm spot size for 0.1–0.2 second and 300–500 mW of energy will usually obliterate these vessels
Bleeding is common,
Gross hyphema may occur
Other uses of lasers Goniopunctures in NPGS is mandatory, after a while,
as during the surgical procedure itself, the AC is left alone.
Goniopunctures are done with a YAG Laser
These help passage of aqueous into the scleral lake.
Blocked inner ostium can be freed by Yag Laser, post trabeculectomy.
Vitriolysis , in case of a vitreous tag sticking out, can be done using a YAG laser.
Modifying bleb by lasers after staining the bleb with gention violet.
Goniopuncture
Lasering the bleb
Lasers in Glaucoma -Summarizing Lasers in glaucoma are an important part of the
armamentarium in the management.
Several situations exist when laser therapy may prove beneficial to the control of intraocular pressure, in association with medical therapy and may enhance quality of life by preserving visual function.