lasers in glaucoma,retina

1. LASERS IN
OPHTHALMOLOGY
Dr. NIKITA JAISWAL

2. HISTORY:
• In 1916, ALBERT EINSTEIN laid the foundation for
invention of laser
• Laser was coined by GURDEN GOULD.
• The first working laser in ophthalmology was made
by THEODORE MAIMAN,1960.
• He utilized a pulsed ruby laser coupled with a
monocular direct ophthalmoscopic delivery system.

3. GLOSSARY
• INTRODUCTION
• PROPERTIES
• TYPES
• LASER –OPHTHAL
RELATION
• APPLICATIONS
• MODE OF DELIVERY
• AREA OF INTEREST

4. L: LIGHT
A: AMPLIFIED BY
S: STIMULATED
E: EMISSION
R: RADIATION

5. INTRODUCTION
PROPERTIES:
• Coherence: wavelengths of the laser light are in
phase in space and time.
• Monochromatic light : beam of single wavelength.
• Collimation: all rays are parallel to each other.

7. Genesis

11. Diode 810nm
Krypton red 647nm
Krypton yellow 568nm
Frequency doubled 532nm
NdYAG
Argon green 514nm
Argon blue 485nm

12. Green Argon laser (514.5 nm)
•It is absorbed selectively at the retinal pigment epithelium (RPE),
hemoglobin pigments, chorio-capillaries, layer of rods and cones
and at the outer and inner nuclear layers.
•It is readily absorbed by the melanin granules.
•It coagulates from chorio capillaries to inner nuclear layer
of the retina.
•It is suitable for photocoagulation of retinal pigment epithelium
(RPE), choroids and blood vessels.

13. Freq-doubled Nd: YAG laser (532 nm)
•Itproduces a pea-green beam.
•It is often termedas “green Nd: YAGlaser” or “KTP
laser”.
•It is more highlyabsorbed by hemoglobin (Hb) and the
melaninpresent inretinal pigment epithelium (RPE) and trabecular meshworkthan the argon laser beam. It
coagulates from choriocapillaries to outernuclearlayerof the retina.
•Itis small and portable likediode laser.
•It is a solid state and diode pumped CWlaser.
•Itcauses photocoagulation with least energy trans-
mission and shows considerable safety in maculartreatment. Hence, it is fast gaining major marketshare of
posterior segment photocoagulator.

14. 1.Krypton red laser (647 nm)
1. Themelaningranules also readily absorb it.
2. It is not absorbed by the hemoglobin (Hb) and xanthophylls pigments present in the maculararea. Hence,it is
particularly suitable for macularphoto- coagulation and coagulation of subretinal neovascular membrane.
3. It coagulates deeper into the retinal pigment epithelium .
4. (RPE) and choroids. It has insignificant photo- coagulation effect onthe vascular system of the retina. Itis less
absorbed and more highlytransmitted throughretinal pigment epithelium (RPE) . So, it is able to produce more
extensive and deep coagulation of choriocapillaries and choroids.

15. Diode laser (810 nm):-
•It is the most important semiconductor laser [GaAlAs (720-890nm)GaAs (810nm)]
•Direct photocoagulation of microaneurysmis difficult becauseit is poorly absorbed by hemoglobin.
•However, it is as effective as argon, freq-doubled Nd: YAG laser in reducingmacular edema.
•It offers increasedpatient comfort due to absence of bright flash of light.
•However, due to deeper penetration in to the choroids, it may bepainful if the intensityof retinal coagulation is
not properly titrated /reduced.
•It is a low cost, portable, small, high powered and versatile laser.

16. Light tissue interactions:
Photocoagulation Photodisruption
Photoablation photoactivation

17. Types:
• Solid state:ruby,Nd:yag
• Gas lasers: argon,krypton,neon,helium
• Excimer: argon fluoride

18. Photocoagulation:
• Laser light is absorbed by the RPE & then it produces heat which
denatures the proteins.
• Light energy applied to tissue changes to thermal energy –tissue
temperature rises by 65’c which causes coagulative necrosis.
• This heat coagulate the pigmented & adjacent tissues.
• The outer layers are more effected than the inner layers.

19. Types of lasers in
photocoagulation
• Green argon laser (514.5 nm)
• Freq doubled Nd:YAG laser (532 nm)
• Krypton red laser (647nm)
• Diode laser(810nm)

20. Photodisruption:
• The energy produced is released in a very short
time.
• The laser beam is focused, concentrating the power
into small area
• It produces a spark & an acoustic wave—which
disrupts the tissue.
• ex:Nd:YAG laser.

21. Photoactivation
• It is a conversion of chemical from one form to
another by light.
• ex-the use of verteporfin –a drug that is chemically
inert but is activated by light ,after which it
destroys neovascular tissue.

22. Photoablation :
Temperaturerise does not take place in the shorter wavelengths of the ultraviolet
spectrum.
At the site of impact, the tissue simply disappears without any charringand temperature
rise.
Surface of the target tissue can be precisely removed, layer-by-layer,in photoablation.
Photoablation with 193 nmargonfluoride (ArF) excimer

24. Laser parameters
Laser Parameters
•Power = Numberof”photons”emitted each second and is
expressed in watts (W).
•Exposure time = Theduration in second (sec.) the “photons”
are emitted ineach burn from thelaser.
•Spot size = Thediameter of the focused laser beam and is
expressed in micron(μm).

25. CLINICAL APPLICATIONS

26. OUR SCOPE :
laser
PCIOL
RETINAL DEGENERATIONS
Glaucoma
LPI
ALT
SLT
Retina
DR/FOCAL /GRID

27. Nd-YAG posterior capsulotomy

30. Pattern of capsulotomy opening
• Cruciate opening: It is the usual choice. Thefirst shot
is made superiorly in the location of some fine tension lines at 12o’ clock and progressing towards 6 o’ clock.
•Christmas tree pattern opening: Thistype of opening is preferred whenthereis increased tendency
to intraocularlens pitting (IOL pitting) or damage due to presence of minimumgap orno gap between posterior
surface of intraocularlens andopacified posterior capsule.
•Revised Hexagonal Capsulotomy technique

32. Follow-up Schedule
Inour countrythe following protocol of follow up is feasible or
advisable.
1st follow up visit –Next day or day after tomorrow. 2nd
follow up visit – One/two weeks.
3rd follow up visit – Four/six weeks.
COMPLICATIONS :
TRANSIENT ELEVATION OF IOP
IOL PITTING
ACUTE GLAUCOMA
RRD
LESS COMMON
IRITIS
HYPHAEMA
MACULAR HOLE
ENDOPHTHALMITIS

33. LASERS IN GLAUCOMA
• ALT
• SLT
• LASER PERIPHERAL IRIDOTOMY

34. Application of continuous wave Argon Laser either
bichromatic blue-green (454.4–528.7 nm ) or mono-
chromatic green ( 514.5 nm ) non penetrating coagulative
burns to the trabecular meshwork ( TM ) results in improved
aqueous outflow.
Laser thermalenergyis absorbed by pigmented trabecularmeshwork.
Possibly this causes increasedspace inintertrabecular space due to shrinkageof collagen fibrils of trabecular
lamellae andleads to increasedaqueous outflow throughthe trabecular mesh-work.
Shrinkageof collagen fibrils also tightens the trabecularmeshwork ringand opens up drainage pores.
Macrophages migrateinto the treated area and engulf extracellular matrix(ECM)..

35. ALT Technique Proper
1.Parameters: Energy:400-1200mW, exposure-0.1 second and spot size-50μ(micron).
2.No.of laser burns: Single session schedule-100burns over entire360 degree. Double session
schedule-50burnsover 180degree intwo sessions at 4 weeks interval.

36. End point of optimal energy effect: Blanching
or tissue whitening with minimal or no
bubble formation Large bubble formation
indicates energy level is too high
If the tissue reaction is inadequate, increase
the energy/power by 200 mW until optimal
end point is achieved by least power.
Site of focus: At the junction of the anterior
nonpigmented and posterior pigmented
trabecular meshwork If properly focused the
laser focus will be perfectly round with a clear
outline.
A = Schwalbe’s Line, B = Nonpigmented
trabecular meshwork, C = Pigmented
trabecular meshwork, D = Scleral Spur and
E= Ciliary Band

37. 1 and 2= Blanching or tissue
whitening with no bubble
formation Ideal, 3 =The
aiming beam is ill focused the
laser focus is oval with blurred
edge unacceptable,
4 =Minimal or small bubble
formation Acceptable,
5 =Slight discoloration
Acceptable and
6 = Large bubble formation 
Indicates too high power setting

Unacceptable,

38. SLT
• Selectiave Laser
Trabeculoplasty” (or
Selective Laser
Trabeculotherapy) is
performed with a
frequency doubled
Nd:YAG laser ( 532 nm ).
It has replaced argon
laser trabeculoplasty
(ALT) due to lack of
damage to the trabecular
meshwork.
• It selectively targets the
melanin granules within the
cells of the pigmented
trabecular meshwork (TM).
Disruption of the melanin
granules cause cell death
termed as “selective
photothermolysis ”.
• There is no structural or
photocoagulative damage
to the trabecular meshwork
(TM).
• Eliminates scarring (seen in
ALT) which is responsible for
reduced aqueous outflow.

40. . Parameters:
Energy—0.6-1mJper pulse (to avoid bubble formation) Pulse
duration—3nanosecond (ns) and
Spot size—400μm.
2.No. of laser burns: 50single short pulses 3ns )
spread over 180 degree of the trabecularmeshwork (inferior/
nasal quadrant).
3.End point of optimal energy effect: Thereis
no end point like blanching or tissue whitening or
bubble formation as seen in ALT
4.Site of focus: Theshots cover entire heightof
trabecular meshwork.
1 = Schwalbe’s Line, 2 = Nonpigmented trabecular
meshwork, 3 = Pigmented trabecular meshwork, 4
=Scleral Spur and 5= Ciliary Band. Left: Argon Laser
Trabeculoplasty-50 μm laser spots at the junction of
the pigmented and nonpigmented trabecular
meshwork, 150 μm apart; Right: Selective Laser
Trabeculoplasty-400 μm confluent laser spots covering
entire height of the trabecular meshwork

42. LPI:

43. Iridotomy Technique
Proper(ARGON)
“Hump” technique: Initially a “hump” is created on the iris with contraction
burn of 500 μm spot size, 200-400 mW energy and 0.5-second exposure. The
hump is penetrated full thickness with 50 μm, 700-1200 mW and 0.1/0.2
second burns.
Drumhead” technique: Initially stretch burns areplaced circularlyaround the
site of iridotomy with 200 μm, 200 mWand 0.2sec. Parametersto create taughtness of
the centralarea like “drumhead”. Thecentral area is penetrated with 50
micron, 700-1200 mW and
0.1/0.2 second burns.

44. ND YAG LPI:
• Insertion of contact
lens: Commonly
Abraham contact
• Lens is used. It has a
+66 diopter peripheral
button over a routine
contact lens

45. Iridotomy Technique Proper
•Usually, 3-8 mJ per shot from Nd: YAG laser andone to three shots are sufficient
to complete the procedure.
•A full thickness opening in iris in one shot is the optimal
target. Often up to four shots areneeded toachieveperforation ofiris.
•Axis of the focusing beam should coincide with the axis of the contact lens.
•Conditions/situations whereuse ofcontact lens is avoided higherenergyis required and
more central iridotomy is to bemade.
•If the anterior chamberdepth is nil, the pulse energyshould not exceed10-12 mJ.

46. •Optimal siteof iridotomy
• Between 10 o’ clock and 2 o’ clock.
• Avoid 12 o’ clock site-here gas bubble
may obstruct the siteof the opening.
• Will becoveredby the uppereyelid.
• About three-fourth of the distance between
pupillary margin and iris periphery.
• Avoid arcus senilis —The opacity interferes with
clear focus and transmits less laser energy.
• Avoid visible iris vessels.

47. 1.Follow-up Schedule Thefollowing protocol is suggested:
1st follow up—next day or day after tomorrow.
1. 2nd follow up—one week postlaser.
2.3rd follow up—three weeks postlaser.
3.4th follow up—six weeks postlaser.

48. Retinal lasers

50. Laser delivery systems:
Indirect ophthalmoscope
Slit lamp biomicroscope
Endophotocoagulation

52. Know what we have……

55. Burn intensity
light Barely visible retinal blanching
mild Faint white retinal burn
Moderate Opaque,dirty white retinal burn
heavy Dense-white retinal burn

57. OCULAR TISSUES LIGHT ABSORBED LIGHT PASSED
MELANIN GREEN,YELLOW,RED
& INFRAREDS
XANTHOPHYLL BLUE YELLOW & RED
HAEMOGLOBIN BLUE, GREEN & YELLOW RED

58. Practical aspects of laser
photocoagulation
• Anaesthesia:topical,peribulbar/retrobulbar
• Lenses:2 types of contact lenses
1-negative-power planoconcave lenses.
2-high-plus-power lenses.
Negative power -Upright image with superior resolution.
-favoured for macular treatment
-provide the same retinal spot size.
High plus power -Inverted image
-Offer a wide field of view
-provide a spot size that is magnified
over the laser setting size.

59. Choice of laser wavelength:
• Focused on the degree to which photocoagulation must be targeted to a
particualr tissue sparing the normal tissue.
• Area directly related to intensity & duration of irradiation.
Lasers characteristic Preferred
Green laser Absorbed well by
melanin & Hb
Retinal vascular
abnormalities/CNV
Red laser Good penetration &
cause deeper burns
Moderate vitreous
hemorhages
Yellow laser Minimal scatter & little
potential for
photochemical changes.
Retinal vascular &
choroidal
neovascularizarion

60. PRP
• Gas laser
• Mechanism: PHOTOCOAGULATION
• 514.5 nm wavelength(visible)
INDICATIONS
• Diabetic retinopathy
• Macular edema
• CRVO/BRVO
• Eales disease
• sickle cell retinopathy,coats disease

61. photocoagulation
INDICATIONS:
RETINAL ISCHEMIA
PDR
NVD
LASERS:ARGON GREEN,DIODE,KRYPTON

62. PRP/Scatter Photocoagulation Technique Proper
1.PRP is usually divided over 3 sessions with 1-2week(s) interval between thesessions.
2.TheDiabetic Retinopathy Study (DRS) protocol recommended 800-1600burnsin PRP.
However, 1800-2200burns are often reported.
3.Location of PRP burns—Itextends from 500 μm nasal to the optic disc margin, 2DD(3000
μm) temporal to, above and below the macular center, just within the
vascular arcade and extending peripherally to or beyond the
equator.

63. SITTING:
• 3 SITTINGS
• INTERVAL 1-3 WEEKS
• 1800 applications of 500 µm retinal spot size,0.1 to 0.2 sec duration
(180mw to start with)
SESSION SPOT SIZE POWER EXPOSURE
1ST 100-200µm 100-400mw 0.05-0.2 sec
2ND 300-500µm 400-800 mw 0.1-0.2 sec
3RD 300-500
µm
400-800 mw 0.1-0.2 sec

66. Modertae to heavy laser
burns
Laser in PRP

68. FOCAL PHOTOCOAGULATION:
SPOT SIZE EXPOSURE POWER
50-100µm 0.1 SEC 100-400mw
: Areas 5oo µm away from disc margin &
centre of macula but within within 3000µm

69. complications
• Paracentral scotoma
• Transient increase of edema
• Photocoagulation scar expansion
• Subretinal fibrosis at laser site
• Inadvertent foveolar burns

70. Grid photocoagulation
Indication: Previously untreated areas of
diffuse leakage in the retina
-Areas 5oo micron away from disc margin &
centre of macula are excluded
Grid laser is usually placed on papillo-macular
bundle
Spot size exposure Power
50-200µm 0.1 sec 50-100mw
Lasers used:- argon green & yellow

72. Retinal degeneration:
• Parameters
• Spot size—500-800
μm
• Exposure—0.1-0.2
sec.
• Power—*400-600
mW
• Pattern—Usually
solitary, linear, single
row and interrupted
(interval = 1⁄2 of spot
size)

73. 1.Thephotocoagulation burnsshould beplaced at least 1 DD (Disc diameter) i.e. 1500 μm
away from theborder of
2.the peripheral retinal degeneration.
3.Initially, most anteriormargins are photocoagulated.
4.If thedegeneration is extensive or considerable vitreous
5.traction is present, initial single row of coagulation may be reinforcedbydouble row of
linear, interrupted coagulation

74. Pattern scan laser:
• This is done in single spots with pulse durations of
10 to 20 ms rather than conventional 100-200 ms
• Multispot laser delivers multiple uniform laser burns
simultaneously by a single foot pedal depression in a
variety of pattern.
• Patterns are:-
Pattern Retina Macula
Square arrays 5*5
Arcs Concentric rows
varying from 1 to 3
Exclusion zone upto
2mm
circular For small hole

75. Disadvantages
• The spot size is restricted (100,200& 400micron)
• Inability to design the pattern
• It produces some more noise.
• Difficulty in penetration through media opacities.

76. Micropulse laser:
• This was invented by pankratov in 1990 in this the laser
energy in short-pulse or in micropulse.
• Parameters:- retinal spot size,laser energy & duration
constant, size of retinal lesion is governed by DUTY CYCLE.
• Longer the OFF time between pulses lesse will be
the duty cycle= less damage to tissue & less heat
produced.
Cumulative refraction
time between pulses.

78. Take home seminar message:
1. ultraviolet photokeratoconjunctivitis (also
known as ‘welder’s flash’ or simply ‘photo- keratitis’.
2.one aspect of ‘snow-blindness’ from wavelengths of ~180-
400 nm)
3.ultraviolet cataract (~295-325 nm – and perhaps to 400 nm).
This is expected only from chronic exposure under normal.
4. Choice of lasers should be based on the type of tissue we
are interested in.
5.Photocoagulation temp. of treated tissue is raised from 37’c
to 50’c
6.Argon green and diode lasers are delivered through
Laser Endoscope during vitrectomy.