laser types and uses laser is acronym of LIGHT amplification bt stimulated emmision of Radiations

1. LASER in Ophthalmology
By:
Saif ullah Email ID: optomsaif.4all@hotmail.com
FIACLE, M.PHIL OPTM, MPH, BS OPTM
Assistant Professor Optometry
PIO, Al-Shifa Trust Eye Hospital

2. LASER:
• the word laser was initially an acronym for Light Amplification by Stimulated
Emission of Radiation (LASER) .
• It means that when an electron receive energy in the form of photon it jumps to its
outer most shell or high energy level.
• These electrons are unstable in higher state so they loose their energy and jump
down to its lower energy state.
• An electron may stay in a metastable state for minutes or longer.
• A photon of appropriate frequency passing near such an electron will stimulate the
electron immediately to drop to a lower state and radiate an identical photon.

5. • Although the total energy in laser light may be slight, it can be focused on
a very small area to produce a very high energy density.
• Laser light is also highly directional
• Lasers may operate continuously ( eg, an argon laser photocoagulator) or
in pulses ( eg, a YAG laser for capsulotomy).
• Mode locking and Q-switching are 2 common methods of producing a
pulsed output.

6. Properties of Laser
 Coherency
 Monochromatism
 Collimated
 Constant Phasic Relation
 Ability to be concentrated in short time interval
 Ability to produce non linear effects
Llight waves travel parallel to each other in a single
direction with weaker divergence

7. Pulsed and Contineous Laser
 Pulsed – energy delivered in brief bursts, more power
 Examples: Nd YAG, Excimer lasers
 Continuous – Argon, krypton lasers, diode lasers, and dye lasers

8. 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.

9. Wavelengths of Laser Light

10. Electromagnetic Spectrum

11. Basic Components of Laser
 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

12. Laser Tissue Interaction:
• Laser surgery involves l of 4 light-tissue interactions:
– photocoagulation
– photoablation,
– photodisruption, or photoactivation.
Usually -
Visible Wavelength : Photocoagulation
Ultraviolet Yields : Photoablation
Infrared : Photodisruption
Photocoagulation

13. Photocoagulation
• Photocoagulation is the process by which heat generated by the
absorption of light denatures proteins.
• Pigmented tissue absorbs light and converts it to heat, which denatures
(coagulates) the pigmented and adjacent tissues.
• Retinal photocoagulation was first performed by focusing sunlight onto
the retina using a heliostat.
• Sunlight was replaced by a xenon light source, which was ultimately
replaced by a variety of lasers. During retinal photocoagulation, laser light
is absorbed by
• the retinal pigment epithelium (RPE), and the heat produced denatures
(coagulates) the retinal proteins.

14. • The outer retinal layers are more affected than are the inner layers, a fact
that has several clinical implications.
• The more edematous the retina, the less heat reaches the inner layers and
the less visible the laser burn.
• Accordingly, when photocoagulating an edematous retina, it is important
to look for signs of photocoagulation occurring in the deeper retinal
layers.
• The difficulty with coagulating the inner retinal layers is the reason laser
photocoagulation is often ineffective in preventing the progress of
retinoschisis, especially when only the innermost layers split.
• Controlling laser spot size and duration is crucial.

15. (A) Head-mounted binocular indirect ophthalmoscopy laser under general anaesthesia; (B) appearance immediately following laser
photocoagulation for type 1 disease

16. Photoablation
• It uses high-energy ultraviolet photons to break covalent chemical bonds.
• An excimer laser, for example, generates photons at a wavelength of 193
nm;
• these photons are absorbed by and break the covalent bonds in corneal
collagen, thereby vaporizing the collagen molecules.
• Because the energy of photoablation is used only to break bonds, no heat
is produced and the technique does not scar adjacent tissue.
• Presently, photoablation is used only for keratorefractive procedures.

17. Fig. 7.16 Corneal (Photo ablation ) during photorefractive keratectomy

18. Photodisruption
• The posterior capsule is transparent to visible and near-infrared light,
including the 1.06-f.lm wavelength produced by the Nd-YAG laser.
• This type of laser is pulsed, so the energy it produces is released in a very
short time, producing a large momentary power.
• Also, the laser beam is focused, concentrating the power into a small area.
• In the vicinity of the focus, electrons are stripped from their atoms by
ionization, but they quickly recombine, which produces a spark and an
acoustic wave that mechanically disrupts the posterior capsule.

19. (A) Vacuolated or pearl-type; (B) Elschnig pearl formation
(arrow) following laser capsulotomy; C: laser pitting of an IOL

20. Photoactivation
• Photoactivation is the conversion of a chemical from one form to another
by light.
• Vision itself depends on the photoactivation (cis-trans isomerization) of
rhodopsin in photoreceptor outer segments.
• A clinical application of photoactivation includes the use of verteporfin, a
drug that remains chemically inert until activated by light, after which it
destroys neovascular tissue e.g. Photo Dynamic Therapy in New Vascular
AMD.

21. LASER TREATMENT OF
FUNDUS DISORDERS
 Diabetic Retinopathy
 Retinal Vascular Diseases
 Choroidal Neovascularization (CNV)
 Clinical Significant Macular Edema (CSME)
 Central Serous Retinopathy (CSR)
 Retinal Break/Detachment
 Tumour

22. Cont’d
 ARMD
 Retinal Vein Occlusion
 Eale’s Disease
 Coats Disease
 Peripheral Retinal Lesion
 Retinopathy of prematurity

23. 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

25. Pathogenesis of diabetic macular edema

29. Retinal hemorrhage

30. 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

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

32. What is PDT ?
 Visudyne (Verteporfin)
 Selective Damage
of SRNVM.
 Costly.

33. Retinoblstoma
before treatment
Retinoblastoma after thermotherapy