ROLE OF LASERS IN OPHTHALMOLOGY

Presenter : Dr. Ajay Gulati

HISTORY

Dates to 400 BC, when Plato described the dangers of direct sun gazing during an eclipse

Czerny and Deutschmann, in 1867 and 1882, respectively, focused sunlight through the dilated pupils of rabbits

Meyer-Schwickerath undertook the study of retinal photocoagulation in humans in 1946 using the xenon arc lamp

The first functioning laser was demonstrated by Maiman in 1960. The active laser material was a ruby which emitteda radiation of 649 nm (red light) pulsed with a xenon flash lamp

First clinical ophthalmic use of a laser in humans was reported by Campbell et al. in 1963 and Zweng et al. in 1964

Argon laser was developed in 1964, L’Esperance conducted the first human photocoagulation with it

He also introduced the frequency-doubled neodymium:yttrium-aluminum-garnet (Nd:YAG) and krypton lasers in 1971 and 1972, respectively

Q-switched , mode-locked , tunable dye laser , semiconductor infrared diode laser were other sequential discoveries

INTRODUCTION

LASER stands for Light Amplification by Stimulated Emission of Radiation

The basic laser cavity consists of an active medium in a resonant cavity with two mirrors placed at opposite ends. One of the mirrors allows partial transmission of laser light out of the laser cavity, toward the target tissue. A pump source introduces energy into the active medium and excites a number of atoms. In this manner, amplified, coherent, and collimated light energy is released as laser energy through the mirror that partially transmits. The various lasers differ mainly in the characteristics of the active medium and the way this active medium is pumped

Properties of laser light that make it useful to ophthalmologists

MonochromaticitySpatial coherenceTemporal coherenceCollimationAbility to be concentrated in a short time

intervalAbility to produce nonlinear tissue

effects

Laser physics

TYPES

Carbon Dioxide

Neon

Helium

Krypto n

Argon

Gas

Nd Yag

Ruby

Solid State

Gold

Copper

MetalVapour

Argon Fluoride

EXCIMER Dye Diode

LASERS

Tissue Interactions

Carbon Dioxide(Photo vaporisation)

Neon

Helium

Krypton(Photo coagulatn)

Argon(Photo coagulatn)

Gas

Nd Yag(Photo coagulatn)(Photo disruption)

Ruby(Photo coagulatn)

Solid State

Gold(Photo dynamic)

Copper

MetalVapour

Argon Fluoride(Photo ablation)

EXCIMER Dye(Photo coag.)

(Photo dynamic)

Diode(Photo coag.)

LASERS

DELIVERY SYSTEMS

Slit-lamp biomicroscope : most common, delivery is transcorneal, with or without the aid of contact lenses

Indirect ophthalmoscope : condensing lens , transcorneal

Endolaser probes : fiber-optic probes used within the eye

Exolaser probes : fiber-optic probes used trans-sclerally

PARAMETERS AND TECHNIQUES

Wavelength: choice of optimal wavelength depends on the absorption spectrum of the target tissue

PRINCIPAL WAVELENGTHS OF COMMONLY USED LASERS 193 nm - Excimer (Cornea) 488 - 514 nm - Argon (Retina) 532nm - Frequency doubled Nd:YAG 694.3 nm - Ruby 780 - 840 nm - Diode 1064 nm - Nd Yag (Capsule) 10,600 nm - Carbon dioxide (Skin)

Other Parameters

Power

Exposure Time

Spot Size

TISSUE EFFECTS OF LASER

PHOTORADIATION (PDT):

Also called Photodynamic Therapy

Photochemical reaction following visible/infrared light

particularly after administration of exogenous chromophore.

Commonly used photosensitizers:

Hematoporphyrin

Benzaporphyrin Derivatives

Photon + Photosensitizer in ground state (S)high energy triplet stage Energy Transfer Molecular Oxygen Free Radical S + O2 (singlet oxygen), Cytotoxic Intermediate Cell Damage, Vascular Damage , Immunologic Damage

Photoablation:

Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy, Argon Fluoride (ArF) Excimer Laser.

Photocoagulation:

Laser Light

Target Tissue

Generate Heat

Denatures Proteins (Coagulation)

Rise in temperature of about 10 to 20 0C will cause coagulation of tissue.

PhotovaporizationVaporization of tissue to CO2 and water occurs when its

temperature rise 60—100 0C or greater.

Commonly used CO2

Absorbed by water of cells

Visible vapor (vaporization) Heat Cell disintegration Cauterization Incision

Photodisruption:Mechanical Effect:

Laser Light

Optical Breakdown

Miniature Lightening Bolt

Vapor

Quickly Collapses

Thunder Clap

Acoustic Shockwaves

Tissue Damage

MODES OF OPERATION

Continuous Wave (CW) Laser: It deliver the energy in a continuous stream of photons.

Pulsed Lasers: Produce energy pulses of a few tens of micro to few mili second.

Q Switched Lasers: Deliver energy pulses of extremely short duration (nano second).

Mode-locked Lasers: Emits a train of short duration pulses (picoseconds) to femtoseconds

Pulsed pumping

Safety

Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is

Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players.

Class II/2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power, for example laser pointers.

Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.

Class IIIb/3B can cause immediate eye damage upon exposure. Class IV/4 lasers can burn skin, and in some cases, even

scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.

Warning symbol for lasers

USES

DIAGNOSTIC THERAPEUTIC

DIAGNOSTIC

Scanning Laser Ophthalmoscopy

Laser Interferometry/ Optical Coherence Tomography

Wavefront Analysis

Scanning Laser Ophthalmoscopy

In the scanning laser ophthalmoscope (SLO), a narrow laser beam illuminates the retina one spot at a time, and the amount of reflected light at each point is measured. The amount of light reflected back to the observer depends on the physical properties of the tissue, which, in turn, define its reflective, refractive, and absorptive properties. Media opacities, such as retinal hemorrhage, vitreous hemorrhage, and cataract, also affect the amount of light transmitted back to the observer. Because the SLO uses laser light, which has coherent properties, the retinal images produced have a much higher image resolution than conventional fundus photography.

study retinal and choroidal blood flowmicroperimetry, an extremely accurate mapping of the

macula’s visual field.

Tests Performed on the Scanning Laser Ophthalmoscope

Scanning Laser Acuity Potential (SLAP) Test: The letter E corresponding to different levels of visual acuity (ranging from 20/1000 to 20/60) is projected directly on the patient’s retina. The examiner directs the test letters to foveal and/or extrafoveal locations within the macula, and determines a subject’s potential visual acuity.

This is especially helpful in individuals who have lost central fixation but still possess significant eccentric vision.

Microperimetry / Scotometry : The SLO could visualize a particular area of the retina and test its sensitivity to visual stimuli, thereby generating a map of the seeing and non-seeing areas.

Hi-Speed FA / ICG Fluorescein and Indocyanine Green Angiography (FA/ICG)

performed using the SLO is recorded at 30 images per second, producing a real-time video sequence of the ocular blood flow

Optical Coherence Tomography

diode laser light in the near-infrared spectrum (810 nm) partially reflective mirror used to split a single laser beam into two, the measuring

beam and the reference beam measuring beam is directed to the retina , laser beam passes through the neurosensory retina

to the retinal pigment epithelium (RPE) and the choriocapillaris. At each optical interface, some of the laser light is reflected back to the OCT’s photodetector

reference beam is reflected off a reference mirror at a known distance from the beam splitter, back to the photodetector. The position of the reference mirror can be adjusted to make the path traversed by the reference beam equal to the distance traversed by the measuring beam to the retinal surface. When this occurs, the wave patterns of the measuring and reference beams are in precise synchronization, resulting in constructive interference. This appears as a bright area on the resulting cross-sectional image. However, some of the light from the measuring beam will pass through the retinal surface and will be reflected off deeper layers in the retina. This light will have traversed a longer distance than the reference beam, and when the two beams are brought back together to be measured by the photodetector, some degree of destructive interference will occur, depending on how much further the measuring beam has traveled. The amount of destructive interference at each point measured by the OCT is translated into a measurement of retinal depth and graphically displayed as the retinal cross-section.

OCT images are displayed in false color to enhance differentiation of retinal structures. Bright colors (red to white) correspond to tissues with high reflectivity, whereas darker colors (blue to black) correspond to areas of minimal or no reflectivity. The OCT can differentiate structures with a spatial resolution of only 10 μm

Wavefront Analysis and Photorefractive Keratectomy

Lasers are used in the measurement of complex optical aberrations of the eye using wavefront analysis

Hartmann-Shack aberrometer

Therapeutic Uses

• Lids and Adnexae • Anterior Segment & Posterior Segment

Lids and Adnexae

Skin: (usually CO2 laser) Lid Tumors : carbon dioxide laser ,benign and

malignant ,bloodless but scarring, lack of a histologic specimen, and inability to assess margins.

Blepharoplasty (carbon dioxide or erbium:YAG laser ) Xanthalesma ( green laser) Aseptic Phototherapy Pigmentation lesion Laser Hair Removal Technique Tattoo Removal Resurfing

Lacrimal Surgery Endoscopic Laser Dacryocystorhinostomy

Anterior Segment

Conjunctival / Corneal Growths, Neovascularization

Refractive Surgery

Laser in Glaucoma

Laser in Lens

Refractive Surgeries

Photorefractive keratectomy

Laser subepithelial keratomileusis (LASEK)

Laser-assisted in situ keratomileusis (LASIK)

Photorefractive keratectomy

low myopia (up to 6D) and low hyperopia (up to 3D)

LASIK jjj

2 to 9 D

lamellar dissection with the microkeratome

refractive ablation with the excimer laser

IntraLASIK/Femto-LASIK or

All-Laser LASIK ( corneal flap is made with

Femtosecond laser microkeratome)

Suction Ring Microkeratome Flap Removed

LASIK Flap replaced Post operative

Femto lasers in cataract surgery

LenSx Lasers (ALCON)new level of precision and reproducibilityThe Laser creates a) Corneal incisions with precise dimensions and

geometry.b) anterior capsulotomies with accurate centration

and intended diameter, with no radial tears.c) lens fragmentation (customized fragmentation

patterns)

Lasers in Glaucoma

Laser treatment for internal flow block

Laser treatment for outflow obstruction

Miscellaneous laser procedures

Laser treatment for internal flow block

Laser peripheraLiridotomy

&

Laser iridopLasty (GoniopLasty)

Laser peripheraLiridotomy

ND:YAG Laser iridotomy : Q-switched Nd:YAG lasers (1064 nm)

2–3 shots/burst using approximately 1–3 mJ/burstopening of at least 0.1 mm.

Argon or Solid-State Laser iridotomy: Photocoagulative (lower energy & longer exposure)

Iris color (pigment density) is the most imp factor Iris color can be divided into three categories: a) light brown : 600–1000 mW with a spot size of 50 µm

and a shutter speed of 0.02–0.05 second b) dark brown: 400–1000 mW , spot size of 50 µm and a

shutter speed of 0.01 second c) blue iris: 200- µm spot, 200–400 mW, 0.1 Second to anneal the pigment epithelium to the stroma ,

Then the spot size reduced to 50 µm and power increased

to 600–1000 mW at 0.02–0.1 second to perforate

Complications of Laser iridotomy

IritisPressure elevationCataractHyphemaCorneal epithelial injuryEndothelial damageFailure to perforateLate closureRetinal burn

Laser Iridoplasty (Gonioplasty)

Plateau iris & Nanophthalmos: 100–200- µm spot size , 100–30 mW at 0.1 second , 10- 20 spots evenly distributed over 360º

Laser treatment for outflow obstruction

Laser TrabeculoplastyExcimer Laser TrabeculostomyLaser Sclerostomy

Laser trabeculosplasty (LTP) :a) Argon laser trabeculoplasty (ALT) : 50 µm

spot size and 1000-mW power for 0.1 second , 3–4° apart 20–25 spots per quadrant

b) Selective Laser trabecuLopLasty (SLT) : Q-switched, frequency-doubled 532-nm Nd:YAG laser 400-µm spot , 0.8 mJ , 180° with 50 spots or 360° with 100 spots , 3–10 ns

COMPLICATIONSIritisPressure elevationPeripheral anterior synechiaeHyphema

Excimer Laser Trabeculostomy((ELT)

precise and no thermal damage to surrounding tissues

ab-interno (used intracamerally) : 308-nm xenon-chloride (XeCl) excimer laser delivers photoablative energy

Laser sclerostomy

Nd:YAG laser, the dye laser, 308-nm XeCl excimer laser, argon fluoride excimer laser, erbium:YAG laser, diode lasers, the holmium:YAG laser etc .

Ab-externo : probe applied to the scleral surface under a conjunctival flap.

Ab-interno : through a goniolens

Miscellaneous laser procedures

CyclophotocoagulationLaser suture lysis (LSL)Reopening Failed Filtration sitesLaser synechialysisGoniophotocoagulationPhotomydriasis (pupilloplasty)

Cyclophotocoagulation

Trans-scleral CyclophotocoagulationA) Noncontact Nd:YAG laser

cyclophotocoagulationB) Contact Nd:YAG laser

cyclophotocoagulationC) Semiconductor diode laser trans-scleral

cyclophotocoagulation

Endoscopic cyclophotocoagulation (ECP)

Laser suture lysis (LSL)

When lasering sutures, the flange of the Hoskins laser suture lens holds up the lid. The suture is located under the laser slit lamp

lens is pressed steadily against the conjunctiva, displacing edema until a clear image of the suture is seen . The suture usually is treated near the knot. The long end of the suture will then retract into the sclera

Laser synechialysis : lyse iris adhesions

Goniophotocoagulation: anterior segment neovascularization , rubeosis , fragile vessels in a surgical wound

Photomydriasis (pupilloplasty) : enlarge the pupillary area by contracting the collagen fibers of the iris

Lasers In Lens

Posterior Capsular Opacification : (Nd:YAG) laser posterior capsulectomy

Laser posterior capsulectomy

Cruciate pattern Circular pattern

Posterior Segment

Laser in vitreous

Laser in Retinal vascular diseases

Other Retinal diseases

Laser in vitreous

Vitreolysis in cystoid macular edema

Viterous membranes & traction bands

Laser Photocoagulation In Vascular Diseases

Panretinal Laser Coagulationa) Full Scatter Panretinal Laser Coagulationb) Mild Scatter Panretinal Laser CoagulationFocal Laser ApplicationSubthreshold Laser Coagulation for

Retinal Disease

Full Scatter Panretinal LaserCoagulation

Diabetes : four accepted indications for a dense (full scatter) panretinal laser coagulation are

a) Presence of vitreous or preretinal hemorrhageb) Location of new vessels on or near the optic disk (NVD) c) Presence of new vessels “elsewhere” (NVE)d) Severity of new vessels (proliferation area greaterthan one-fourth of the optic disk size)exposure times 100–200 ms ,a spot size of 500 μm. The laser

application should lead to a mild white retinal lesion. The distance between the laser spots 0.5–1 laser spot. range of laser spots varies between 1,000 and 2,000 . It is recommended to apply laser lesions in Two to four sessions, 2 weeks apart , Regression expected after 4–6 weeks

Central Retinal Vein Occlusion: main complications of a central vein occlusion apart from macular edema are neo-vascularizations of the retina and of the iris

no effect of prophylactic pan-retinal laser coagulation to prevent neovascularizati-ons of the iris. But if neovascularizations of the retina or of the iris exist,the treated eyes clearly benefit from full scatter panretinal laser coagulation

Branch Retinal Vein Occlusion: characterized by macular edema and vitreous hemorrhage from retinal neovascularizations

Retinal laser coagulation done not earlier than 3–6 months.

done only if retinal hemorrhage has significantly cleared.

For the treatment of macular edema, exposure times of 100 ms and a spot size of 100 μm are recommended. The distance of 2–3 spot diameters. The area of the edema should be treated in a dense grid. After occurrence of neovascularizations a sector retinal laser coagulation is indicated.

Mild Scatter Panretinal LaserCoagulation

For Non-proliferative diabetic retinopathyrisk factors for treating non PDRThe 4:2:1 rulea) If either intraretinal bleeding occurs in 4

quadrantsb) Or if venous beading occurs in at least 2 quadrantsc) Or if intraretinal microvascular abnormalities (IRMA) occur in at least one quadrant

600 laser spots of 500 μm ,exposure times 100–200 ms spots more spaced than full scatter.

Focal Laser Application

Clinically significant macular edema (CSME) It is present and should be treated by focal laser

coagulation if:a) There is a clinical retinal thickening within 500

μm distance from the center of the maculab) There is hard exudation within 500μm distance

from the center of the macula with retinal thickening in the bordering retina

c) There is a retinal thickened area by the size of at least one papilla diameter within the distance of

one papilla diameter from the center of the macula

Placement of the laser coagulation spots has to be decided by fluorescein angiography

exposure times 100ms and a spot size of 100 μm with beginning power of 70–80 mW.

leads to a mild gray retinal lesion.

Subthreshold Laser Coagulation forRetinal Disease

Selective treatment of the RPEDiabetic macular edemaCentral serous retinopathy (CSR)Drusen in age-related macular degeneration

(AMD)

Focal diabetic macular edema before treatment bySRT

The same fundus 2h after SRT–the lesions are visibleonly in the fluorescein angiogram and show the pattern of treatment

Fundus image 6 months after SRT. The hard exudateshave resolved

Photodynamic therapy (PDT)

Indications

CNVs due to age-related macular degeneration, pathologic myopia, angioid streaks and presumed ocular histoplasmosis syndrome

Retinal capillary hemangiomaVasoproliferative tumorParafoveal teleangiectasis

For age-related macular degeneration and pathologic myopia : i.v Verteporfin at 6mg/m2 BSA over 10 mins. Five minutes after the cessation of infusion, light exposure (laser emitting light of 692 nm) with an irradiance of 600 mW/m2 is started, delivering 50 J/cm2 within 83 s .

Angiod Streaks: light dose of 100 J/cm2 over an interval of 166 s

Other Uses Of Lasers in Post. Segment

Drainage of subretinal fluid / haem

Retinal Breaks or Tears

Intraocular tumors (RB , Melanomas )

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