LASERS IN OPHTHALMOLOGY

LASERS IN OPHTHALMOLOGY

Dr Yasser Ibraheem Abdullah
Brief outline
Introduction.
History .
Laser physics.
Classification .
Laser tissue interactions.
Uses – therapeutic - diagnostic.
Complications.

INTRODUCTION

LASER is an acronym for:
•L : Light
•A : Amplification by
•S : Stimulated
•E : Emission of
•R : Radiation
Term coined by Gordon Gould. Lase means to absorb energy in one form and to emit a new form of light energy which is more useful.


LASER Vs. LIGHT

Stimulated emission

Spontaneous emission
Monochromatic
Polychromatic
Highly energized
Poorly energized
Parallelism
Highly divergence
Coherence
Not coherent
Can be sharply focused
Can not be sharply focused
LASER LIGHT

PROPERTIES OF LASER LIGHT

•Coherency
•Monochromatism
•Collimated
•Constant Phasic Relation
•Ability to be concentrated in short time interval
•Ability to produce nonlinear effects


LASER PHYSICS
•Light as electromagnetic waves, emitting radiant energy in tiny package called ‘quanta’/photon. Each photon has a characteristic frequency and its energy is proportional to its frequency.
•Three basic ways for photons and atoms to interact :
Absorption
Spontaneous Emission
Stimulated Emission

HOW LASER WORK ???

Continuous and pulsed lasers
•Pulsed – energy delivered in brief bursts, more power •Examples: Nd YAG, Excimer lasers
•Continuous – Argon, krypton lasers, diode lasers, and dye lasers

CLASSIFICATION OF LASER

Solid State Ruby Nd.Yag Erbium.YAG
Gas Ion Argon Krypton He-Neon CO2
Metal Vapour Cu Gold
Dye Rhodamine
Excimer Argon Fluoride Krypton Fluoride Krypton Chloride
Diode Gallium-Aluminum Arsenide (GaAlAs)


THREE TYPE OF OCULAR PIGMENT
•Haemoglobin : Argon Green are absorbed , Krypton yellow. These laser are found to be useful to coagulate the blood vessels.
•Xanthophyll : Present in inner and outer plexiform layers of macula. Maximum absorption is blue. Argon blue is not recommended to treat macular lesions.
•Melanin : RPE, Choroid Argon Blue, Krypton Pan Retinal Photocoagulation, and Destruction of RPE

ELECTROMAGNETIC SPECTRUM

LASER SAFETY
• Class-I : Causing no biological damage.
•Class -II : Safe on momentary viewing but chronic exposure may cause damage.
•Class -III : Not safe even in momentary view.
•Class -IV : Cause more hazardous than Class -III.

LASER SAFETY REGULATION:

•Patient safety is ensured by correct positioning.
•Danger to the surgeon is avoided by safety filter system.
•Safety of observers and assistants.

LASER TISSUE INTERACTION

LASER VARIABL TISSUE VARIABLE
Wavelength


Transparency

Spot Size

Water Content

Power

Pigmentation

Duration

LASER TISSUE INTERACTION
LASER

TISSUE

Thermal Effect Photo- chemical Ionizing Effect

Photocoagulation Photoablation

Photoradiation Photovaporization
Photodisruption


THREE BASIC LIGHT TISSUE INTERACTIONS

Photocoagulation:

Laser Light Target Tissue Generate Heat Denatures Proteins (Coagulation)
Rise in temperature of about 10 to 20 0C will cause coagulation of tissue.

2- Photo disruption:

•Mechanical Effect:
Laser Light Optical Breakdown Miniature Lightening Bolt Vapor Quickly Collapses Thunder Clap Acoustic Shockwaves Tissue Damage

3- Photoablation:

•Breaks the chemical bonds that hold tissue together essentially vaporizing the tissue, e.g. Photorefractive Keratectomy, Argon Fluoride (ArF) Excimer Laser.
Usually -
Visible Wavelength : Photocoagulation
Ultraviolet Yields : Photo ablation
Infrared : Photo disruption
Photocoagulation

PHOTOVAPORIZATION

•Vaporization of tissue to CO 2 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

PHOTOCHEMICAL EFFECT

PHOTORADIATION (PDT:(
•Also called Photodynamic Therapy
•Photochemical reaction following visible/infrared light particularly after administration of exogenous chromosphere.
•Commonly used photosensitizers:
Hematoporphyrin
Benzaporphyrin Derivatives
e.g. Treatment of ocular tumour and CNV

Photon + Photosensitizer in ground state (S)

3S (high energy triplet stage)

Energy Transfer

Molecular Oxygen, Free Radical , S + O2 (singlet oxygen) , Cytotoxic Intermediate

Cell Damage, Vascular Damage , Immunologic Damage

IONISING EFFECT
•Highly energized focal laser beam is delivered on tissue over a period of nanosecond or picoseconds and produce plasma in target tissue. •

Q Switching Nd.Yag

Ionization (Plasma formation)

Absorption of photon by plasma

Increase in temperature and expansion of supersonic velocity

Tissue Disruption Shock wave production

iridotomy
THREE BASIC COMPONENTS
•A Laser Medium
e.g. Solid, Liquid or Gas
•Exciting Methods
for exciting atoms or molecules in the medium
e.g. Light, Electricity
•Optical Cavity (Laser Tube)
around the medium which act as a resonator

MODES OF LASER OPERATION

•Continuous Wave (CW) Laser: It deliver their energy in a continuous stream of photons.
•Pulsed Lasers: Produce energy pulses of a few tens of micro to few mili second.
• Q Switches Lasers: Deliver energy pulses of extremely short duration (nano second).
•A Mode -locked Lasers: Emits a train of short duration pulses (picoseconds).
•Fundamental System: Optical condition in which only one type of wave is oscillating in the laser cavity.
•Multimode system : Large number of waves, each in a slight different direction ,oscillate in laser cavity.

Delivery systems

1- Transpupillary: - Slit lamp
- Laser Indirect Ophthalmoscopy
2- Trans scleral - Contact
- Non contact
3- Endophotocoagulation.


Slit lamp biomicroscopic laser delivery
•Most commonly employed mode for anterior and posterior segment.
•:ADVANTAGES
1- Binocular and stereoscopic view.
Fixed distance.
Standardization of spot size is more accurate.
Aiming accuracy is good.

Laser indirect ophthalmoscope.

• Advantages
Wider field(ability to reach periphery).
Better visualization and laser application in hazy medium.
Ability to treat in supine position.(ROP/EUA)
difficulty in focusing.
• Disadvantage
Difficulty to standardize spot size.
Expensive.
Un co -operative patient.
Learning curve.

USES

•THERAPEUTIC.
•DIAGNOSTIC.


LASER IN ANTERIOR SEGMENT
CORNEA: Laser in Keratorefractive Surgery:
•Photo Refractive Keratectomy (PRK).
•Laser in situ Keratomileusis (LASIK).
•Laser Sub epithelial Keratectomy (LASEK).
•Epi Lasik. Laser Thermal Keratoplasty .
•Corneal Neovascularization.
•Retrocorneal Pigmented Plaques.

EXCIMER LASER

•High energy UV laser.
•Excited dimer.
•Argon fluoride( 193nm) most commonly applied for corneal surgeries.
•Photoablation.
•Laser removes approximately 0.25microns of corneal tissue with each pulse.
•Amount of tissue to be ablated derived from “munnerlyn equation”
•Central ablation depth in microns=diopters of myopia*(ablation zone diameter in mm)2 3

FEMTOSECOND LASER

ADVANTAGES:
•Flap are more accurate and uniform in thickness.
•Centration of flap is easier.
•Better adherence to underlying stroma.
•Patient are more comfortable.
DISADVANTAGES:
•Suction break
•Costly


LASER IN GLAUCOMA
•Laser Iridotomy.
•Laser Trabeculoplasty (LT(
•Selective Laser Trabeculoplasty
•Trabecular ablation
•Gonioplasty (Iridoplasty, Iridoretraction)
•Pupilloplasty
•Sphincterotomy
•Iridolenticular Synechiolysis
•Goniophotocoagulation
•Goniotomy

Laser Filtration Procedures (sclerostomy):

•Ab Externosclerostomy (Holmium)
•Ab Internosclerostomy (Nd.YAG) 1- Contact 2- Non -contact
• Cyclodestructive Procedures (cyclophotocoagulation(
•Transscleral Cyclophotocoagulation
•Trnaspupillary Cyclophotocoagulation
•Diode Laser Endophotocoagulation

PUPILLOPLASTY

2-3 rows of burns circumferentially 1mm away from the pupillary margin. Innermost row:8spots, 200micron size, 200-400mW. Outer row:10- 12spots,400micron size,300- 500mW


Stretching the updrawn pupil
Laser parameters are same for photomydriasis.
Burns are placed along the inferior margin.

ARGON LASER TRABECULOPLASTY

Mechanism of action :Mechanical.
Biological.

LASER IN LENS

•Posterior capsulotomy
•Laser phacoemulsification
•Phacoablation.
•Laser in Lacrimal Surgery: Laser DCR.

LASER IN VITREOUS

•Vitreous membranes
•Vitreous traction bands

LASER TREATMENT OF FUNDUS DISORDERS

•Diabetic Retinopathy
•Retinal Vascular Diseases
•Choroid Neovascularization (CNV)
•Clinical Significant Macular Edema (CSME)
•Central Serous Retinopathy (CSR)
•Retinal Break/Detachment
•Tumour
•ARMD
•Retinal Vein Occlusion
•Eale’s Disease
•Coats Disease
•Peripheral Retinal Lesion
•Retinopathy of prematurity.


Informed consent
•Patient should be explained about the
possible complications to avoid legal problems
to the treating physician later.

CLASSIFICATION OF CHORIORETINAL BURN INTENSITY

•Light : Barely visible retinal blanching
•Mild : Faint white retinal burn
•Moderate : Opaque dirty white retinal burn
•Heavy : Dense white retinal burn

DIABETIC RETINOPATHY

TYPE OF RETINOPATHY THERAPY

Background

Control of diabetes, regular review
Maculopathy CSME
Focal photocoagulation
Diffuse leakage around macula
Grid laser
Circinate
Focal photocoagulation
Pre-proliferative Retinopathy
Frequent review
Proliferative retinopathy
Pan retinal photocoagulation
Advanced diabetic eye disease
Vitreoretinal surgery with photocoagulation


Retinal breaks and tears
Laser settings Wavelength :argon green, Nd YAG,dye yellow red , diode.
Duration :0.1-0.2seconds.
Retinal spot size: 200- 500microns.
Intensity : moderate retinal whitening

Choroidal melanoma

Indication:
1-Photocoagulation technique.
2-Initial destruction of the surrounding choroidal blood supply-1-2rows -200-500 microns 0.5-1sec-intense burn.
3-Direct tumour photocoagulation-low energy burns long duration5-30sec.

What is PDT ?

 Visudyne (Verteporfin)
 Selective Damage of SRNVM.
 Costly.

Standard Clinical Treatment Parameters for Visudyne PDT

•1 . Dye dose = 6 mg/m2 body surface area
•2 . Intravenous infusion over 10 min
•3 . Treatment at 15 min after start of dye infusion
•4 . Laser light wavelength of at 689 nm, irradiance of 600 mW/cm2 and fluence of 100 J/cm2


Trans pupillary thermotherapy
•Thermotherapy can involve using
•ultrasound, microwave, or infrared radiation to deliver heat to the eye.
•Retinoblastoma -application of diode (infrared) laser to the tumor surface in regions of disease activity.
• Goal- cause tumor cell death by raising the temperature of tumor cells to above 45°C for ~1 min, thus reducing blood supply and producing apoptosis.
PAttern SCAn Laser(PASCAL(
•The PASCAL Photocoagulator is an integrated semi -automatic pattern scan laser photocoagulation system designed to treat ocular diseases using a single shot or predetermined pattern array.
•.Nd:YAG laser: Laser source
•or laser indirect ophthalmoscope (LIO) slit lamp Delivery device:
• Control system for selecting power and duration •Method for selecting spot size
.

DIAGNOSTIC USE OF LASERS

•Scanning Laser Ophthalmoscopy
•allows for high -resolution, real-time motion images of the macula without patient discomfort.
•SLO angiography: to study retinal and choroidal blood flow.
•May be used to perform microperimetry, an extremely accurate mapping of the macula’s visual field.

Optical Coherence Tomography

•Uses diode laser light in the near -infrared spectrum (810 nm) to produce high-resolution cross-sectional images of the retina using coherence interferometry.


Complications
•General complications : - Pain - Seizures.
•Anterior segment complications:
Elevated IOP.
Corneal damage.
Iris burns.
Crystalline lens burns.
IOL and PC damage.
Internal opthalmoplegia.
Choroidal detachment and exudative RD.
Choroidal ,subretinal and vitreous hemorrhage
Thermal induced retinal vascular damage.
Preretinal membranes.
Ischaemic papillitis.
Paracentral visual field loss and scotoma.
Photocoagulation scar enlargement.
Subretinal fibrosis.
Iatrogenic choroidal neovascularisation.
Accidental foveal burns.