Different types of lasers and laser delivery system
1. DIFFERENT TYPES OF
LASERS AND DELIVERY
SYSTEM
PRESENTER - DR. KRATI GUPTA
MODERATOR - DR. HEMLATA DEKA
2. WHAT IS LASER?
• 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.
3. HISTORY OF LASER
• 1917 -Sir Albert Einstein laid the foundations for the laser.
• 1958 - C.H. Townes, A.L. Schawlow: Theoretical basis for lasers.
• 1960 - Theodore Maiman : Built first laser using a ruby crystal.
• 1963 - C. Zweng: First medical laser trial (retinal coagulation).
• 1965 - W.Z. Yarn: First clinical laser surgery.
• 1970- The excimer laser was invented in by Nikolai Basov.
• 1971 -Neodymium yttrium aluminum garnet (Nd-YAG) and Krypton laser developed.
4. PROPERTIES OF LASER
• Monochromatic (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)
5. HOW IS LASER PRODUCED?
• Light is emitted in the form of 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
12. THREE TYPES OF OCULAR PIGMENT
• Haemoglobin:
Hemoglobin in blood vessels absorbs blue, green and yellow light, but
does not absorb red light.
• Xanthophyll
Xanthophyll pigment of the retina absorbs blue light, but passes green,
yellow and red light.
• Melanin:
Excellent absorption by green, yellow, red and infra- red wavelengths.
15. DIFFERENT TYPES OF LASER
Solid State Gas Metal vapour Dye Excimer Diode
Ruby Ion Copper Rhodamine Argon Fluoride Gallium-Aluminium
Arsenide
Nd YAG Argon Gold Krypton Fluoride
ErbiumYAG Krypton Krypton Chloride
Helium
CO2
17. LIGHT TISSUE INTERACTIONS
1. PHOTOCOAGULATION
• In photocoagulation temperature of treated tissue is increased from 37°C to at
least 50°C.
• This results in denaturation of tissue protein and coagulation at the absorbent
tissue site.
• This results from conversion of light energy to heat energy.
• Temperature rise in tissue is proportional to the amount of light absorbed by
the tissue.
18. LIGHT TISSUE INTERACTIONS
1. PHOTOCOAGULATION
• Absorption of the light frequencies is high in :
i. Pigmented trabecular meshwork
ii. Iris
iii. Ciliary body and
iv. Retinal pigment epithelium (owing to melanin)
v. Blood vessels (owing to hemoglobin).
• Lasers commonly used in the type of photocoagulation are:
i. Argon
ii. Krypton,
iii. Diode
iv. Nd:YAG lasers
19. LASERS COMMONLY USED IN PHOTOCOAGULATION
CW GREEN ARGON LASER (514.5 nm)
• It is absorbed selectively at :
• It coagulates from choriocapillaries to inner nuclear layer of the retina.
• It is suitable for photocoagulation of retinal pigment epithelium, choroids and blood
vessels.
i. Retinal pigment epithelium
ii. Hemoglobin pigments
iii. Choriocapillaries
iv. Layer of rods and cones
v. Outer and inner nuclear layers
vi. Melanin granules
20. LASERS COMMONLY USED IN PHOTOCOAGULATION
FREQ-DOUBLED ND: YAG LASER (532 NM)
• It produces a pea-green beam.
• It is often termed as “green Nd: YAG laser” or “KTP laser”.
• It is more highly absorbed by hemoglobin (Hb) and the melanin present in
retinal pigment epithelium (RPE) and trabecular meshwork than the argon
laser beam.
• It coagulates from choriocapillaries to outer nuclear layer of the retina.
21. LASERS COMMONLY USED IN PHOTOCOAGULATION
FREQ-DOUBLED ND: YAG LASER (532 NM)
• It is small and portable like diode laser.
• It is a solid state and diode pumped CW laser.
• It causes photocoagulation with least energy transmission and shows considerable
safety in macular treatment.
• Hence, it is fast gaining major market share of posterior segment photocoagulator.
22. LASERS COMMONLY USED IN PHOTOCOAGULATION
KRYPTON RED LASER(647 nm)
• The melanin granules also readily absorb it.
• It is not absorbed by the hemoglobin (Hb) and xanthophylls pigments present in
the macular area.
• Hence, it is particularly suitable for macular photocoagulation and coagulation of
subretinal neovascular membrane.
• It coagulates deeper into the retinal pigment epithelium (RPE) and choroids.
23. LASERS COMMONLY USED IN PHOTOCOAGULATION
KRYPTON RED LASER(647 nm)
• It has insignificant photocoagulation effect on the vascular system of the retina.
• It is less absorbed and more highly transmitted through retinal pigment epithelium.
• So, it is able to produce more extensive and deep coagulation of choriocapillaries and
choroids.
24. LASERS COMMONLY USED IN PHOTOCOAGULATION
DIODE LASER (810 nm)
• It is the most important semiconductor laser [GaAlAs (720-890 nm) GaAs (810
nm)]
• Direct photocoagulation of microaneurysm is difficult because it is poorly
absorbed by hemoglobin.
• It is as effective as argon, freq-doubled Nd: YAG laser in reducing macular edema.
25. LASERS COMMONLY USED IN PHOTOCOAGULATION
DIODE LASER (810 nm)
• It offers increased patient comfort due to absence of bright flash of light.
• Due to deeper penetration in to the choroids, it may be painful if the intensity of
retinal coagulation is not properly titrated /reduced.
• It is a low cost, portable, small, high powered and versatile laser.
26. LASERS COMMONLY USED IN PHOTOCOAGULATION
DIODE LASER (810 nm)
• Lasers with blue wavelength light should not be used for photocoagulation in following
situations;
1. In the macular area – Xanthophyll pigments absorb blue light maximally and green
light poorly.
Hence, in macular photocoagulation blue light (blue-green argon laser) will cause
unwanted inner retinal damage
2. In older patients – The ageing lens absorbs blue light much more than other light
wavelengths.
The shorterwavelength blue lights are also more scattered by aged crystalline lenses.
27. INFLUENCE OF OPACITIES IN THE OCULAR MEDIA
UPON LASER PARAMETER (POWER)
• Any opacity in the ocular media such as :
• Reduces energy level of the laser beam striking the retinal surface by reflection,
scattering or absorption of the laser beam.
• Hence, the optimum power level should be arrived at by gradually increasing the power
to cause optimum coagulation burn for that procedure.
i. corneal edema,
ii. corneal haziness,
iii. flare and cells in the anterior
chamber
iv. lental opacity and
v. vitreous opacity
31. LASER TISSUE INTERACTION
2. Photoablation
• tissue is removed by light as when intramolecular bonds of biological tissues are
broken, disintegrating target tissues and the disintegrated molecules are volatilized.
• In photoablation, temperature rise does not take place.
• At the site of impact, the tissue simply disappears without any charring and
temperature rise.
• Surface of the target tissue can be precisely removed, layer-by-layer, in photoablation.
• Photoablation with 193 nm argon fluoride (ArF) ,excimer laser.
32. LASER TISSUE INTERACTION
3. Photodisruption
• The temperature of treated localized microscopic area of tissue is increased from 37°C
to 15000°C.
• On optical breakdown at the desired site, electrons are stripped from the atoms of
target tissue resulting in development of plasma (collection of ions and electrons)
• This leads to hydrodynamic and acoustic shock wave, which mechanically tears the
tissue microscopically.
• Photodisrupter lasers are Q-switched and pulsed Nd YAG laser , frequency-doubled Nd:
YAG is commonly used to create a posterior capsulotomy or a peripheral iridotomy.
33. LASER TISSUE INTERACTION
4. Photovaporization
• If laser irradiation higher than those required for photocoagulation is applied to target
tissue, rapidly expanding water vapor can cause tissue disruption (photovaporization).
• This results from a microexplosion when the temperature of water rises above the
boiling point.
• In these situations, photovaporization is usually accompanied by photocoagulation,
providing hemostasis.
• The CO2 laser (10600 nm wavelength irradiation) effectively vaporizes tissues.
• Example of clinical use of these lasers are Holmium: YAG or Erbium : YAG laser
sclerostomy.
34. LASER TISSUE INTERACTION
5. Photoradiation
• Hematoporphyrin derivative is selectively taken up and retained by metabolically
active tumor tissue.
• In photoradiation, this photosensitized tissue is exposed to 630 nm red lights from a
dye laser, producing cytotoxic singlet oxygen and tissue destruction.
• Similarly, Verteporfin preferentially accumulates in choroidal neovascular membrane
(CNV).
• In photodynamic therapy the choroidal neovascular membrane is subjected to laser
emission from diode (689 nm) with resultant occlusion and thrombosis of the
neovascular tissue.
36. MODES OF OPERATION
Continuous Wave (CW) Laser: It delivers the energy in a continuous stream of
photons.
Eg: Argon, Krypton lasers, Diode lasers and dye lasers.
Pulsed Lasers: Produce energy pulses of a few micro to milliseconds, taking
the form of alternating ‘on’ and ‘off’ periods.
Eg: Nd YAG, Excimer Laser.
37. MODES OF OPERATION
Q Switched Lasers: Deliver energy pulses of extremely short duration
(nanosecond).
Mode-locked Lasers: Emits a train of short duration pulses (picoseconds to
femtoseconds) .
Pulsed pumping: Another method of achieving pulsed laser operation is to
pump the laser material with a source that is itself pulsed, either through
electronic charging in the case of flashlamps, or another laser which is
already pulsed.
38. LASER PARAMETERS
• Power = Number of “photons”emitted each second and is expressed in watts (W).
• Exposure time = The duration in second (sec.) the “photons” are emitted in each
burn from the laser.
• Spot size = The diameter of the focused laser beam and is expressed in micron (µm).
Spot size is usually fixed for treatment of a particular lesion.
39. LASER PARAMETERS
• However, the energy (Power × Exposure time) parameters must be decreased
or increased, with the decrease or increase in the spot size parameter.
• The spot size when focused on the retina depends on;
1) Laser Spot Magnification Factor (LSMF) of the laser lens,
2) Spot size selected in the Slit-lamp
3) Refraction of the eye under treatment.
• Energy = Number of”photons”emitted during an exposure of any duration
and is expressed in joules (J).
Energy (Joules) = Power (Watt) × Exposure time (Second)
40. LASER DELIVERY
• Laser can be delivered through 3 types of approach :
1. SLIT LAMP BIOMICROSCOPE
2. LASER INDIRECT OPHTALMOSCOPE
3. INTRAOPERATIVE LASER ENDOSCOPE
41. SLIT LAMP BIOMICROSCOPE
• The most common and popular delivery system.
• Laser parameters viz.; power, exposure time and spot size can be changed.
• Binocular and stereoscopic view.
• Fixed distance.
• Standardization of spot size is more accurate.
• Aiming accuracy is good.
42. LASER INDIRECT OPHTHALMOSCOPE
• Argon green and diode lasers are delivered through a fiberoptic cable.
• Ideal for photocoagulation of peripheral retinal breaks and degenerations.
Ideal for PRP/scatter photocoagulation of extreme retinal periphery in
eyes with rubeosis iridis, PDR, post-CRVO, retinopathy of prematurity etc.
• Ideal for photocoagulation in children under general anesthesia.
• Ideal for photocoagulation in eyes with small pupil, intraocular gas and
lental opacities.
43. LASER INDIRECT OPHTHALMOSCOPE
• Unsuitable for focal and or grid laser of macula.
• Spot size is altered by the dioptric strength of the hand held condensing
lens and moving a lever on the headset.
• Spot size is also altered by the refractive status of the eye.
• The spot size in a hypermetropic eye is smaller than in an emmetropic eye
whereas, the spot size in a myopic eye is larger than in an emmetropic eye.
• In LIO,
Retinal spot size = Power of condensing aspheric
lens × Image plane spot size/60
44. LASER INDIRECT OPHTHALMOSCOPE
ADVANTAGES DISADVANTAGES
Wider field(ability to reach
periphery).
Difficulty in focusing.
Better visualization and laser
application in hazy medium.
Difficulty to standardize spot size
Ability to treat in supine
position.(ROP/EUA)
Expensive.
Learning curve
Patient uncoperation
45. INTRAOPERATIVE LASER ENDOSCOPE
• Argon green and diode lasers are delivered through Laser Endoscope during
vitrectomy.
• Ideal for photocoagulation of retinal surface neovascularization (NVE), peripheral
retinal breaks etc.
• Ideal for photocoagulation of giant retinal tear.
