Laser

1. LASER
By Azmat jehan
Definition =Laser is an acrynoum for light
amplification by stimulated emmission of
radiation. Or laser is a device which produce a
coherent,unidirectinal,monochromatic,intence &
collimated beam of light.
History=The theory was formulated by einstine in
1917 but working principle was explained by
schwlow.first ruby crystal laser was made by dor
maman in 1960.
Krasnor in 1972 produce/develop Q switched laser .it
was a cold laser (ruby laser).
Aron-rosa develop Nd Yag laser in 1981.

2. Instrumentation or Components of laser
1-Lasing medium. 2-Optical cavity. 3-Excitation source
1-Lasing medium. A substance that when stimulated emits light in all
direction.
2-Optical cavity.It is a cavity containing lasing medium and is used to
reflection light from lasing medium back in to it.It typically consist of
two mirrors.At one end the mirror is fully silvered wheras that at
other end the
3-Excitation sourec.For excitation of lasing medium it may be
….Electricaly from power supply
….Lamps
….Other laser.

3. Working principle
 The lasing medium is present within the optical
cavity. Normally the number of atoms in ground
state is higher than those in the excited state .
 When energy is provided the electron by gaining
energy move from lower to higher energy level &
thus atom becomes excited .
 A condition /situation is reached when number of
atoms in excited state become greater ,than those in
the ground state is known as population inversion.
 At this stage the atoms are unstable & thus drop
back to lower energy level by limitation energy in the
form of photon ,this is called spoontanous emission .

4. cont
 These photons are not exactly in phase,when
the excited atoms are hit by the stimulated
energy as a result instead of excitation .
 These atoms loose energy this emission is
called stimulated emission .the photon reflects
to & fro b/w the two mirrors .with each pass the
energy enhances & coherency is gained. some
of these coherent photons lose through
transparent portion of semi silvered mirror
producing laser light.

5. Types
 Laser are mainly divided in to
 Solid laser
 Liquid laser
 Gas laser
 Excimer laser
Solid state laser ,two main types are
 Nd –Yag laser (1064 nm)
(neuodium yatrium alluminium garnet)
 Hruby laser

6. .
 Most common gas laser are HeNe ,other gas laser
included Co2 laser.which emites light in far
infrared ,used for lid surgery.
 Excimer laser =Chlorine & fluorine mixed with inert
gases such as kaypton ,neon & xenon etc are used
for photoablation i.e in refractive error .eg PRK
 Its wave length is 190 nm .it lies in UV region i.e
vacum UV.
 Semiconductor=Also called as diod laser ,they are
not solid laser its wavelenght,is 810 nm.used for
writhing in CD or player or laser printers.

7. Modes of laser
 Mainly two types
 1-continiouse
 2-pulsed
 Continuesd mode laser continously produced laser
and usually photocogolation in result.
 Pulsed laserm produced /provide laser light in
pulsed form most of photodistruption &
photoablation are pulsed laser ,

8. Properties of laser
 Monochromacity
 Laser light is composed of waves of same
wavelength .the monochromacity improves
the focusing characteristics of laser light .
 Directionality
 Laser light is a unidirectional light emit a
narrow beam light that spreads slowly i.e
1mm spreading occur for each metre
travelled .
 Directionality also improves the focussing of
light in to a small spot.

9. Coherence
 Coherency means that all the waves are exactly
in phase i.e in space & time .Coherency
localized to create interferance of laser
interferometer.
Polarization =
 Laser light is linearly polerized light polerization
enhances the transmission through laser
medium & out loss and by reflection.
Intensity
 Intensity is the power light beam per unit area.

10. Effect on living tissues
 The property of light which effect the living tissue
included .
 Waveleght (
 Pulse duration (max duration`~max effect)
 Absorption magnitude
 Laser absorbing tissue
 Laser needs substrate to get absorbed ,these
includes
 Melanin
 Xanthophylls
 Hemoglobin

11. Melanin
 These are present in choroid and RPE,
 Absorption of most of visible portion occur i-e 360-
780 nm.
 XANTHOPHYL
 Yellow pigment present in macula.
 Strongly absorb blue light .
 That is the reason blue light is contraindicated in
macula degeneration.
 Hemoglobin
 Present in RBCs
 Absorb blue ,green ,yellow wavelength.
 Necessary for photocoagulation but not for ablation.

12. Common uses
 Laser is used in industries for
 Welding
 Cutting
 Evaporation
 Communication
 Medical
 Scientific purpose

13. Laser in treating A/S Pathologies
 Laser is used in treatment of A/S pathologies
 Eye lid surgery e.g trichiasis
 Pterigium
 Corneal refractive error treatment (excimer
193nm)
 Glaucoma treatment (argon laser gonioplasty
 Laser iridotomy
 Laser capusoltomy
 It is a prophylaxis to PCO.

14. PRK(Photorefractive keratotomy
 Hyperopia 2-4 D
 Excimer laser is used to ablate the central
optical zone due to which the cornea
becomes thin & iop pushes it making cornea
more curved cover the error.
 Myopia up to 10 D
 Here laser is applied and the periphery is
made thus iop pushes the thin periphery
anterioraly making it less curved little flatter.

15. Uses of in diagnosis investigation
 These include
 CSLO
 OCT
 Laser microperimetery

16. photocoagulation
 It is procedure in which laser is continuously
make to fall on the target tissue as a result
tissue temperature increase and induce
structural change occur in the target tissue.
 e.g. PRP pan retinal photocoagulation .in
diabetic retinopathy macula the whole retina
photocoagulated
 Fused oedema treatment grid form is used in
this laser.
 Focal laser for hard exudate

17. Prophylaxis by laser.
 Retinal laser before R/D can also be sealed
by laser photocoagolation.
 Photodisruption.
 In this type of laserinteraction high power
pulsed laser is used to ionize the target and
rupture the surrounding tissues.
 E.g lid surgery by co2 laser
 Yag laser posterior capusulotomy
 Trabeculectomy
 Iridotomy.

18. Photoabalation
 In this type of tissue laser interaction the
target tissue is ablated by laser application
evaporated.e.g photorefractive keratectomy
in myopia & hyperopia.
 Advantages of laser surgery
 These includes
 The risk of infection introduction eye during
surgery .sergion can perform the sergury
more peripherly and full control.
 Surgery is performed in out setting and
patient can

19. Complecation
 Hyphemea
 Damage to lens
 Cornea abrassion
 Uveitis
 Raise of IOP
 Choroidal haemarage
 Vitreious haemorage
 Fovea burn
 Secondary narrow angle glaucoma
 Tractional R/D etc

20. Preperation of patient for laser
surgery
 Anaesthesia .it depend upon surgery types
so may be topical ,
 Retrobulber .when working near macula
 General .in children
 Pupil costriction .e.g by pilocarpine done in
patient whose going for peripheral iridotomy .
 Uses of contact lenses.

21. Possibilities of laser
 Three possibilities
 Vision can improve
 Vision can not improve however further
detoriation can be prevented.
 Vision may worsen but further detoriation will
be stop.

22. Refractive eeror and laser
 Either be treated by laser
 Male under 22 years
 Female under 20 years
 Myopes
 1-6D(PRK)
 6-12D (LASIK)
 Greater than 12 D (natural lens remove)
 Hyperopia
 1-4D (PRK)
 Greater than 4 D (LASIK)

23. DELIVERY SYSTEM
 Laser can be deliverd to the target through
 Indirect ophthalmoscope
 Indolaser tube to deliver
 Laser light inside the eye in connection with
slit lamp.

24. Saftey in laser room
 Never project un scanned beams in to an
audience.
 Never use mirror and reflectors in laser room.
 Always use saftey googels in the laser room.
 Never deflect laser beams with hand held
mirrors as they are difficult to control and can
direct beams in unexpected ways causing
eye damage.
 Never use mirror or watch crystals to deflect
static beams at shows as you can cause eye
damage to yourself or other spectators.