ROLE OF LASERS IN OPHTHALMOLOGY Presenter : Dr. Ajay Gulati
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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