The document discusses lasers used in ophthalmology. It begins by defining what a laser is in terms of its acronym parts. It then covers laser physics including absorption, spontaneous emission, and stimulated emission. It describes different types of lasers used in ophthalmology like Nd:YAG, excimer, and diode lasers. Applications covered include treatments for glaucoma, cataracts, retinal diseases, and refractive errors. Mechanisms of laser tissue interaction like photocoagulation and photodisruption are also summarized.
2. INTRODUCTION
LASER is an acronym for:
L : Light
A : Amplification (by)
S : Stimulated
E : Emission (of)
R : Radiation
Term coined by Gordon Gould (1959)
3. 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
4. 3 Mechanisms of Light Emission
Atomic systems in thermal equilibrium with their
surrounding, the emission of light is the result of:
Absorption
And subsequently, spontaneous emission of energy
There is another process whereby the atom in an upper
energy level can be triggered or stimulated in phase with
the an incoming photon. This process is:
Stimulated emission
Is an important process for laser action
1. Absorption
2. Spontaneous Emission
3. Stimulated Emission
Therefore 3 process
of light emission:
8. PROPERTIES OF LASER LIGHT
Monochromatism (emit only one wave length)
Coherence (all in same phase-improve focusing )
Polarized (in one plane-easy to pass through media)
Collimated (in one direction & non spreading )
High energy (Intensity measured by Watt J/s)
9. Laser Vs. Light
Simulated emission
Monochromatic.
Highly energized
Parallelism
Can be sharply focussed
Spontaneous emission
Polychromatic
Poorly energized
Highly divergence
Can not be sharply
focussed
10. CLASSIFICATION OF LASER
Carbon Dioxide
Neon
Helium
Krypton
Argon
Gas
Nd Yag
Ruby
Solid State
Gold
Copper
Metal
Vapour
Argon Fluoride
EXCIMER Dye Diode
LASERS
12. Different material produce specific wavelength depending on
their metastable state
Some laser procedures demand wavelengths which do not
correspond to metastable state of any working material
TWO METHODS – increase no. of available wavelengths
1. HARMONIC GENERATION
2. ORGANIC DYE LASER
HARMONIC GENERATION – Causes light to pass through an
optically non linear crystal which doubles its frequency
ORGANIC DYES – Complex chemical structure – large no. of
metastable orbits with different energy
13. Nd:YAG laser
(Neodymium-doped yttrium aluminum garnet) is a crystal that is used
as a lasing medium for solid-state lasers
Nd:YAG lasers typically emit light with a wavelength of 1064 nm, in
the infrared
Applications
Correct posterior capsular opacification
Peripheral iridotomy in patients with angle-closure glaucoma
Frequency-doubled Nd:YAG lasers (wavelength 532 nm) are used for
pan-retinal photocoagulation in patients with diabetic retinopathy
15. LASER TISSUE INTERACTION
LASER VARIABLE:
Wavelength
Spot Size
Power
Exposure time
TISSUE VARIABLE:
Transparency
Pigmentation
Water Content
16. THREE TYPE OF OCULAR PIGMENT
Haemoglobin:
absorbs blue, green and yellow with minimal red wavelength
absorption, useful to coagulate the blood vessels
Xanthophyll:
Macular area
Maximum absorption is blue. minimally absorbs yellow or red
wavelengths
Melanin:
RPE, Choroid
absorbs green, yellow, red and infrared wavelengths
Pan Retinal Photocoagulation, and Destruction of RPE
Effective retinal photocoagulation depends on how well light penetrates
the ocular media and how well the light is absorbed by pigment in the
target tissue
18. Thermal Effects
(1) Photocoagulation:
Laser Light
Target Tissue
Generate Heat
Denatures Proteins
(Coagulation)
Rise in temperature of about 10 to 20
0C will cause coagulation of tissue
20. Thermal Effects
(3)Photovaporization
Vaporization 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 eg..Femtosecond laser
21. Photochemical effects
Photoablation:
Breaks the chemical bonds that hold tissue
together essentially vaporizing the tissue, e.g.
Photorefractive Keratectomy, Argon Fluoride
(ArF) Excimer Laser
22. PHOTOCHEMICAL EFFECT
Photoradiation (PDT):
Also called photodynamic therapy
E.G. Treatment of Ocular tumours and CNV
Photon + Photo sensitizer in ground state (S)
Molecular Oxygen Free Radical
S + O2 (singlet oxygen) Cytotoxic Intermediate
Cell Damage, Vascular Damage , Immunologic
Damage
23. Delivery Systems
Transpupillary - Slit lamp
- Laser Indirect Ophthalmoscopy
Trans scleral - Contact
- Non contact
Endophotocoagulation
27. i. Removal of lid masses
ii. Orbitotomies
iii. Blepharoplasty, Aesthetics (smoothen wrinkles)
iv. Capillary hemangioma, Portwine stain
Therapeutic Uses
A. Extraocular Adnexae
34. Panretinal Photocoagulation
PRP place laser spots in the peripheral retina for
360 degrees sparing the central 30 degrees of
the retina
POWER, SIZE, NUMBER, AND SESSIONS
Recommendations in the ETDRS for an initial
treatment consisted of 1,200 to 1,600 burns of
moderate intensity, 500-μm size, one-half to one-
spot diameter spacing at 0.1-second duration,
divided over at least two sessions
35. Proliferative diabetic retinopathy
Neovascularisation of iris
Severe non proliferative diabetic retinopathy
associated with-poor compliance for follow up-before
cataract surgery-renal failure-one eyed patient
Central retinal vein occlusion, branch retinal vein
occlusion
Indications
36. Focal or Grid Photocoagulation
Macular edema from diabetes or branch vein occlusion
Retinopathy of prematurity(ROP)
Closure of retinal microvascular abnormalities such as
microaneurysms, telangiectasia and perivascular leakage
Focal ablation of extrafoveal choroidal neovascular
membrane
Creation of chorioretinal adhesions surrounding retinal
breaks and detached areas
Treatment of ocular tumors
37. Focal or grid laser settings
50-100 micron spot size, 0.05-0.1 sec( for focal spot size
50micron, for grid 100-200 micron)
Spots must be atleast one burn width apart
Seal specific leaking blood vessels in a small area of the
retina, usually near the macula
38. Pathophysiology Of Focal Laser
Laser energy removes unhealthy RPE cells which
are then replaced by more viable RPE cells
Photocoagulation stimulates the existing RPE cells
to absorb more fluid.
Laser treatment may stimulate vascular endothelial
proliferation and improve the integrity of the inner
blood-retinal barrier
Several theories
39. FEMTOSECOND LASER
Mode-locking is a technique in optics by which a laser can be
made to produce pulses of light of extremely short duration, on
the order of picoseconds (10−12 s) or femtoseconds (10−15s).
Indications
• Clear Corneal Incisions in LASIK
• Cataract Surgery
• Corneal Incision
• Capsulotomy
• Phacofragmentation
40. Chemical : Some lasers require hazardous or toxic substances
to operate (i.e., chemical dye, Excimer lasers)
Electrical : Most lasers utilize high voltages that can be
hazardous
LASER HAZARDS
41. Fire : The solvents used in dye lasers are flammable.
High voltage pulse or flash lamps may cause ignition.
Flammable materials may be ignited by direct beams or
specular reflections from high power continuous wave
Skin :
Acute exposure to high levels of optical radiation may
cause skin burns; while carcinogenesis may occur for
ultraviolet wavelengths (290-320 nm)
LASER HAZARDS
42. Ocular :
Acute exposure of the eye to lasers can cause corneal or
retinal burns (or both)
Chronic exposure to excessive levels may cause corneal or
lenticular opacities (cataracts) or retinal injury
Laser light in the visible to near infrared spectrum can cause
damage to the retina resulting in scotoma (blind spot in the
fovea). This wave band is also know as the "retinal hazard
region".
Laser light in the ultraviolet (290 – 400 nm) spectrum can cause
damage to the cornea and/or to the lens.
Ocular Hazards