3. 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 l
ight energy which is more useful.
4. HISTORY
• 1960 : The first laser was built by Theodore
Maiman using a ruby crystal medium.
• 1963 : The first clinical ophthalmic use of laser
in humans.
• 1968 : L Esperance developed the argon laser.
• 1971 : Neodymium yttrium aluminum garnet
(Nd.YAG) and Krypton laser develop.
• 1983 : Trokel developed the eximer laser.
5. LASER Vs. LIGHT
LASER
Stimulated emission
Monochromatic.
Highly energized
Parallelism
Coherence
Can be sharply focussed.
LIGHT
Spontaneous emission.
Polychromatic.
Poorly energized.
Highly divergence
Not coherent
Can not be sharply focussed.
6. PROPERTIES OF LASER LIGHT
• Coherency
• Monochromatism
• Collimated
• Constant Phasic Relation
• Ability to be concentrated in short time interval
7. LASER PHYSICS –
HOW LASER Produced
• Light as electromagnetic waves, emitting radiant energy in tiny packag
e called ‘quanta’/photon. Each photon has a characteristic frequency a
nd its energy is proportional to its frequency.
• Three basic ways for photons and atoms to interact:
Absorption
Spontaneous Emission
Stimulated Emission
11. 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)
12. THREE TYPE OF OCULAR PIGMENT
• Haemoglobin:
Argon Green are absorbed , Krypton yellow. These laser are fo
und 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
14. 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.
17. Photothermal (photocoagulation and photo
vaporization)
• Photothermal effects include photocoagulation and photovaporizati
on.
• In photocoagulation, absorption of light by the target tissue results i
n a temperature rise, which causes denaturization of proteins.
– Typically, argon, krypton, diode (810) and Frequency doubled ND:YAG lasers.
• Photovaporization occurs when higher energy laser light is absorbed
by the target tissue, resulting in vaporization of both intracellular an
d extracellular water.
• The advantage of this type of tissue response is that adjacent blood
vessels are also treated, resulting in a bloodless surgical field.
– The carbon dioxide laser, with its wavelength in the far infrared, uses this m
ethod of action.
18. Photochemical (photoablation and photora
diation)
• Photochemical effects include photoradiation and photoablation.
• In photoradiation, intravenous administration of photosensitizing ag
ent, which is taken up by the target tissue, causes sensitization of the targe
t tissue.
• Exposure of this sensitized tissue to red laser light induces the formation of
cytotoxic free radicals.
– Photodynamic therapy (PDT) is an example of photoradiation therapy
• Photoablation occurs when high-energy laser wavelengths in the f
ar ultraviolet (< 350 nm) region of the spectrum and are used to break long
-chain tissue polymers into smaller volatile fragments.
• The exposure times in the photoablation process is usually much shorter (n
anoseconds) compared to photoradiation.
– Excimer laser is a photoablative process.
19. Photoionizing (photodisruption)
• In Photoionization high-energy light is deposited over a short i
nterval to target tissue, stripping electrons from the molecules
of that tissue which then rapidly expands, causing an acoustic s
hock wave that disrupts the treated tissue.
– The ND:YAG laser uses this "photodisruptive" mechanism.
21. MODES OF LASER OPERATION
• Continuous Wave (CW) Laser: It deliver their energy in a continuous str
eam 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 (picoseco
nds).
22. Delivery systems
• Transpupillary: - Slit lamp
- Laser Indirect
Ophthalmoscopy
• Trans scleral : - Contact
- Non contact
• Endophotocoagulation.
23. Slit lamp biomicroscopic laser delivery
• Most commonly employed mode for anterior and pos
terior segment.
ADVANTAGES:
• Binocular and stereoscopic view.
• Fixed distance.
• Standardization of spot size is more accurate.
• Aiming accuracy is good.
24. Laser indirect ophthalmoscope.
Advantages :
• Wider field(ability to reach periphery).
• Better visualization and laser application in hazy medi
um.
• Ability to treat in supine position.(ROP/EUA)
Disadvantage :
• difficulty in focusing.
• Difficulty to standardize spot size.
• Expensive.
• Un co-operative patient.
26. 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.
27. EXCIMER LASER
• High energy UV laser.
• Excited dimer.
• Argon fluoride(193nm) most commonly applied for corneal sur
geries.
• Photoablation.
28. EXCIMER LASER(contd…)
• Laser removes approximately 0.25microns of corneal tissue wi
th each pulse.
• Amount of tissue to be ablated derived from “munnerlyn equa
tion”
• Central ablation depth in microns=diopters of myopia*(ablatio
n zone diameter in mm)2
3
45. DIAGNOSTIC USE OF LASERS
• Scanning Laser Ophthalmoscopy
• allows for high-resolution, real-time motion images of the mac
ula without patient discomfort.
• SLO angiography: to study retinal and choroidal blood flow.
• May be used to perform microperimetry, an extremely accurat
e mapping of the macula’s visual field.
46. Optical Coherence Tomography
• Uses diode laser light in the near-infrared spectrum (810 nm) t
o produce high-resolution cross-sectional images of the retina
using coherence interferometry.
47.
48.
49. Complications
• General complications:
• Pain
• Seizures.
• Anterior segment complications:
Elevated IOP.
Corneal damage.
Iris burns.
Crystalline lens burns.
IOL and PC damage.
Internal opthalmoplegia.
51. Complications(contd..)
• Ischaemic papillitis.
• Paracentral visual field loss and scotoma.
• Photocoagulation scar enlargement.
• Subretinal fibrosis.
• Iatrogenic choroidal neovascularisation.
• Accidental foveal burns.
52. Lasers can….
Save a child’s eye as in Retinoblastoma.
Change a personality as in LASIK.
Cure a middle aged person with Glaucoma.
Restore Vn. in a person with After-Cataract.
Preserve & Retain Vn. in pts. with DR & ARMD
The possibilities are endless…...
53. References
YANOFF AND DUKER OPHTHALMOLOGY- 3rd edition.
LASERS IN OPTHALMOLOGY
A practical guide-AIIMS.
LASER SURGERY OF THE POSTERIOR SEGMENT- Steven M. Bloo
m
