The document discusses laser technology and its applications in ophthalmology. It begins by defining what a laser is and describing its key properties such as coherency, monochromaticity, collimation, and ability to concentrate energy. It then discusses different laser types (pulsed, continuous), operation modes (CW, Q-switched), wavelengths used, and basic laser components. The main laser tissue interactions - photocoagulation, photoablation, photodisruption, and photoactivation - are explained. Applications of laser treatment for various posterior segment diseases are covered, including diabetic retinopathy, CNV, CSR, and tumors.

1. By
Mutahir Shah
Resident M Phil VS
Pakistan Institute of Community
Ophthalmology
HMC Peshawar.
Laser (Introduction and Indication
in Posterior Segment Diseases

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 (inphase)
 Monochromatism
 Divergence
 Collimated (perfectly align and parallel)s
 Ability to be concentrated in short time interval

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.
 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. What is PDT ?
 Visudyne (Verteporfin)+ Laser 689 nm
after 15 minutes of the start of infusion.
 Selective Damage
of SRNVM.
 Costly.

22. 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
 Tumor

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

24. 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

26. Pathogenesis of diabetic macular
edema

30. Retinal hemorrhage

31. Retinal breaks and tears
Laser settings
Wavelength :argon
green,
Duration :0.1-
0.2seconds.
Retinal spot size:
200-500microns.
Intensity : moderate
retinal whitening

32. 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.

33. Retinoblastoma
before treatment
Retinoblastoma after
thermotherapy

34. Diode laser cycloablation;

35. Thank