2. INTRODUCTION
LASER is an acronym for:
L : Light
A : Amplification (by)
S : Stimulated
E : Emission (of)
R : Radiation
3. GORDON GOULD
“LASER”
SIR ALBERT EINSTEIN
Foundation of laser
1917
MEYER SCHWICKERATH
Focused sunlight for surgery
1940
THEODORE MAIMAN
Built first laser-ruby
crystal medium
1960
NICOLAY G .BASOV
Invention of excimer
laser.
1970
DANIELE ARON ROSA
YAG laser for
capsulotomies
1982
4. LASER PHYSICS
• QUANTUM THEORY - electrons in atoms (or molecules) exist in non-
radiating states and each state is associated with a specific energy level
• Each element or compound has a unique distribution of energy states.
• E = hν
• (the difference in energy (E)
• PHOTON characteristic frequency (ν)
• (h) is the Planck constant)
5. Two basic ways for
photons and atoms to
interact:
• STIMULATED
ABSORPTION.
• SPONTANEOUS
EMISSION
6. PROPERTIES OF LASER
• Not a very efficient light source
• Compared with the amount of energy required to power a laser, the amount
of energy produced is modest
• Monochromatic – one colour
• Coherence – in phase with one another-improves focusing
• Collimated – less than 0.1degree divergence.
7. LASERS – NAMED AFTER ACTIVE MEDIUM.
SOLID STATE
• Ruby
• Nd:yag
• Erbium:yag
• Titanium-
sapphire
GAS
• Argon
• Krypton
• Helium
• Neon
• Carbon
dioxide
METAL VAPOUR
• Copper
• Gold
9. TYPES OF OPHTHALMIC LASERS
LASER TYPE WAVELENGTH TYPICAL
PULSE
DURATION
INTERACTION
CO2 9.2-10.8 um CW or ms Pulsed thermal
Nd : YAG 1064 nm (λ/2 = 532nm) 100ps-CW Plasma + thermal +mech
Diode 635-1550 nm Few ns - CW Thermal +photochemical
Ruby 694 nm 1-250 um Thermal
Argon ion 488, 514 nm CW or ms pulsed Thermal
Krypton ion 531 , 568 , 647 nm CW or ms pulsed Thermal
He Ne 633 nm CW Imaging
10. COMPONENTS OF LASER SYSTEM
3 Vital Components
1. Lasing Medium
2. Pumping Source
3. Optical Resonator
11. 1. Lasing medium
Substances having the property to lase
A collection of atoms/molecules/ions that emit radiation in the optical part of
the electromagnetic spectrum.
It may be a solid, liquid or gas
Nature of the lasing medium determines the nature of the emitted radiation
(wavelength /colour)
12. 2. Pumping source
A source of external energy that activates lasing medium
Generates a stimulating photon which in turn causes stimulated
absorption and population inversion.
May be an electrical discharge, heat, flashlamp or ionising radiation.
13. 3. Optical resonator
Amplifies the generated radiation and creates a much powerful beam.
Consists of Brewester windows that allows passage of light to a pair of
mirrors, one totally reflective and the other partially reflective.
The no.of resonating cycles varies greatly amongst the various lasers.
15. Laser delivery
3 basic systems
Slit lamp
Laser indirect ophthalmoscope
(LIO)
Endolaser
Routes
Trans pupillary
Trans scleral
Interaction with ocular tissue
Contact
Non contact
16. 1. Slit lamp bio-microscopic laser delivery
Most commonly employed mode for anterior and posterior
segment.
ADVANTAGES
Binocular and stereoscopic view
Fixed distance
Increased magnification
Standardization of spot size is more accurate
Aiming accuracy is good.
17. 2. Laser indirect ophthalmoscope
ADVANTAGES
Wider field
Better visualization and laser application
in hazy medium.
Ability to treat in supine position.
DISADVANTAGES
Difficulty in focusing.
Expensive
Learning curve
19. Types of ocular pigment
• Macular Xanthophyll:
• Present in inner and outer plexiform layers,
confined to fovea. absorbs blue light but passes
green , yellow , red.
• Haemoglobin in blood vessels absorbs blue ,
green and yellow light but not red.
• Melanin in RPE and choroid absorb all visible
wavelengths. Excellent absorption by green ,
yellow , red and infrared wavelengths.
21. Absorption of laser
light by tissue
Rise in temperature
of tissue and local
inflammation and
scarring
Denaturation of
proteins -
TISSUE
BURNS
Eg., Argon , Krypton , diode (810nm) , frequency doubled ND:YAG
laser.
PHOTOCOAGULATION
22. Beam absorbed
by target
tissue
Increase in tissue
temperature
Critical boiling
point of tissue – gas
bubble formation
Vaporization of
intracellular and
extracellular water.
– TISSUE BURNS
• Micro-explosions
PHOTOVAPOURISATION
Eg., carbon dioxide laser with far –
infrared wavelengths
23. PHOTOIONIZING – PHOTODISRUPTION
• Instantaneous
electric field
generation
INTENSE ENERGY ON
SMALLAREA – target
tissue
• Production of
plasma –
creating a shock
wave
STRIPS ELECTRON
FROM TARGET ATOM
• Photons
emitted
DISRUPTION
(cutting) OF
TARGET TISSUE
Eg: ND:YAG , Femtosecond
24. PHOTO-ABALATION
Laser in far ultraviolet
wavelength is used
(<350 nm)
Breakage of long
chain tissue polymers
(Interatomic bonds)
Converts them into smaller
volatile fragments that
diffuse away
- TISSUE ETCHING
Eg: EXCIMER laser
26. Argon blue-green laser
Mixture of 70% blue (488nm) and 30% green (514nm) light.
Most commonly employed for retinal photocoagulation and trabeculplasty.
Photocoagulation aims to treat the outer retina and spare the inner retina to
avoid damaging the nerve fiber layer.
Absorbed selectively at RPE, Hemoglobin, choriocapillaries, layer of rods
and cones and outer and inner nuclear layers.
Coagulates from RPE to nerve fiber layer.
Not used now due to more damage to nerve fiber layer
27. Frequency doubled Nd:YAG LASER
Most commonly used laser.
Produces a green beam. Wavelength – 532nm
Highly absorbed by Hemoglobin and melanin pigment.
Coagulates from RPE to ONL.
Causes coagulation with least energy transmission and shows considerable
safety in macular treatment also.
28. Krypton red laser
Absorbed readily by Melanin.
Not absorbed by Xanthophyll and hemoglobin and hence it is suitable for macular
photocoagulation.
Wavelength - 647nm.
Coagulates deeper into RPE and choroids. Insignificant effect on vascular system
of retina.
Painful due to deeper penetration into choroid.
29. Diode lasers
Emits an infrared wavelength of 810nm.
Absorbed only by melanin, hence used for macular
photocoagulation.
Also penetrates the sclera.
Used for grid laser. PRP, Transpupillary thermo therapy and Diode
cyclophotocoagulation.
30. Excimer lasers
• High energy ultraviolet light – 1975
• Corneal application – Trokel and Srinivasan in 1983
• Gas mixture : rare gas + halogen
Rapidly
dissociates –
emitting uv light
(Argon Fluoride
– 193nm)
Highly unstable
rare gas- halide
molecule
Application
of high
voltage
current
(30,000eV)
31. Femtosecond laser
Infrared laser with a wavelength of 1053nm.
• Photodisruption
• FS laser has pulse duration in
the femtosecond range (10-15 second)
APPLICATIONS :
• LASIK flap creation
• stigmatic keratotomy (AK)
• presbyopia correction
• channel creation for implantation of intrastromal corneal ring segments (ICRS)
• intrastromal presbyopia correction (INTRACOR)
33. Pre laser work-up
4 components
1. Basic work up
2. Adjunctive Diagnostic procedures
3. Selection of type of lenses and Anaesthesia
4. Patient counselling.
34. Laser management of diabetic retinopathy
Photocoagulation has remained the only established non-invasive
mode of treatment for diabetic maculopathy and proliferative
retinopathy.
The argon blue-green laser has been traditionally used, though of
late solid state frequency-doubled 532 nm YAG (green) laser is
used.
35. Mechanism of action
In Proliferative Retinopathy
Direct destruction of neovascular complex.
Destruction of hypoxic/ischemic area that produces vasoproliferative
factors.
Convert hypoxic retina to anoxic retina thereby more retinal blood is
available to nourish the remaining retina.
Decreased oxygen requirement of inner retina.
Produce chorioretinal adhesion that resists against vitreo-retinal traction
force.
36.
37. • All focal leaks located between
500µm and two disc diameters
(=3000µm) are treated directly
• Initially, 50 to 100µm spots at 0.1
second duration are used to produce
whitening or microaneurysm.
• Focal lesions located 300 to 500 µm
from the centre of the macula are
treated if visual acuity was <20/40
Focal laser photocoagulation
Focal laser around neovascular tuft
38.
39. GRID LASER PHOTOCOAGULATION
• Areas of diffuse leakage are treated
• 50 to 200µm spot size burns placed one
burn width apart , at 0.1 second
duration
• Laser is done in c shaped manner
within the vascular arcades and
avoiding papillomacular bundle.
• Burns must be atleast 500µm away
from the disc margins.
• About 100 to 200 spots may be
necessary.
40. Modified grid laser
Area of papillo-macular bundle is spared.
Direct focal photocoagulation of leaking micro-aneurysm is added.
Special Precautions:
Accurate localization of foveal centre to avoid burns close to fovea (within
300 µm of the foveal centre.
Intense burn is avoided by starting the initial burns with lower power setting
(50 – 100mW) and gradually increasing (increment of 10-20mW) to achieve
optimal light intensity burns
41. SCATTERED PRP indications
Panretinal photocoagulation (PRP) is indicated for any eye with
high-risk PDR
rubeosis iridis
neovascular glaucoma
When the compliance for follow-up is doubtful, even without HRC
42. SCATTERED PRP PARAMETERS
• 200 to 500µm spot size.
• 0.2 to 0.5 second duration
• Burn intensity – moderate (150-
400mWatt) and the burns must be ½ to 1
burn width apart.
• 1800 to 2200 burns are given.
• The whole retina other than the posterior
pole within 3000µm (vascular arcade)
from foveal centre and 500µm from disk
margin are treated.
43. Subthreshold diode micropulse laser
photocoagulation
Uses a 810 nanometer diode laser.
Desired effect is to reduce the laser damage to ocular tissue.
In micropulse mode, the laser energy is delivered with a train of repetitive
short pulses (typically 100x300 msec each) in packets.
The limitation is the difficulty of the treatment without the feedback of an
ophthalmoscopically visible endpoint.
Minimizing the chorio-retinal laser damage allows confluent therapy and re-
treatment of the same areas, which may be needed in macular edema.
44.
45. SIDE EFFECTS OF PRP
Delayed dark adaptation
Mild restriction of peripheral visual fields.
Vitreous hemorrhage may occur from new vessels during treatment and is
best stopped by pressure on the eye with the laser contact lens.
Treatment at any given sitting of more than 1000 burns has risk for the
iatrogenic development of CME, choroidal effusion, exudative retinal
detachment, and angle closure.
46. FOLLOW UP
The first routine follow-up visit is scheduled for 4-6 weeks following the completion
of the PRP.
Supplemental treatment (usually only after 6-8 weeks of completion of PRP) is
recommended for
if retinopathy progresses despite treatment
if a patient has shown good regression of disease initially, and, in the course of follow-
up, shows new neovascularization.
In cases with severe VH or traction , surgical intervention is advised.
Vitrectomy removes the scaffolding for neovascular growth and also removes possible
stimuli for new vessel growth.
48. VENOUS OCCLUSIONS
Branch and central vein occlusion represent the second most frequent cause
of retinal vascular disturbance, after diabetic retinopathy.
The amount of visual and retinal damage is related to the geographic area
drained by the occluded vein, the extent of occlusion, and the ability of the
surrounding vessels to develop collaterals.
49. BRVO
The two most significant vision-threatening complications of branch vein
occlusion are macular edema and retinal/optic disc neovascularization.
INDICATIONS
1. Grid Laser—Persistent macular edema responsible
for ≤ 6/12 (or 20/40) vision with intact perifoveal
capillary network, late accumulation of flouroscein at
the fovea, in BRVO of at least 3 months duration.
2. Scatter/PRP—Retinal neovascularisation (NVE
and or NVD), in BRVO of at least 3 months duration.
CONTRAINDICATIONS
1. Macular non-perfusion
2. Reduced visual acuity due to
RPE changes
50. GRID LASER IN BRVO
PARAMETERS
Exposure time—100msec.
Spot size—100-200 μm
Intensity of burn-light, 1 burn/spot
size width apart
Location and pattern—Same as for
grid laser in diabetic maculopathy
The grid laser may extend upto the border
of the FAZ i.e.; 500 μm from the macular
center and from arcade to arcade.
Areas of capillary leak.
Areas of papillomacular bundle.
Areas of retinal hemorrhages avoided.
51. Scatter prp in brvo
It may be done either in
combination with grid laser or
alone for treatment of NVE
and or NVD.
New vessels are found
usually at the junction of the
normal and ischemic retina.
PARAMETERS
Exposure time—100msec.
Spot size—200-500 μm
Intensity of burn-moderate, 1 burn/spot size width
apart.
Location and pattern of scatter-Same as for scatter/PRP
in diabetic retinopathy. Only the sector/segment of
retina affected by capillary non-perfusion in BRVO.
52. Follow up in brvo
Follow up schedule—Every 4 months
1st follow up-4 months postlaser
* FFA is a must in 1st follow up
*If macular edema persists along with diminished visual acuity, additional
grid photocoagulation may be considered.
*If neovascularization persists or aggravates additional scatter laser may be
considered.
2nd follow up-8 months post laser.
53. Sector laser in an eye with long standing superotemporal BRVO
and macular exudates
54. CRVO
In CRVO, the collaterals develop on the optic disc between the retinal and
choroidal circulation. In ischemic CRVO, new vessels usually develop on
the iris (NVI) and angle of the anterior chamber/trabecular meshwork
(NVA).
TIMING OF LASER
CRVO patients should be examined at monthly interval during immediate 6-
month post CRVO period. Routine undilated slit-lamp examination and
gonioscopy is a must to detect early new vessels iris (NVI) and angle of the
anterior chamber/trabecular meshwork (NVA) in monthly check ups.
55. INDICATION FOR LASER IN CRVO
Indication
1. Prompt/immediate PRP Laser—(a) In ischemic CRVO with rubeosis iridis
(NVI) and or NVA. (b) In ischemic CRVO with NVE and or NVD.
2. Prophylactic PRP Laser—In CRVO when close follow up is not possible.
Macular grid laser has got no role even in CRVO with macular edema. Only
PRP is done in CRVO when indicated.
High-risk characteristics in CRVO
• Visual Acuity <6/60 (or 20/200)
• Angiographically extensive areas of capillary nonperfusion.
56. PRP/SCATTER LASER IN CRVO
Parameters
Exposure time—100-500msec.
Spot size— 500-1000 μm
Intensity of burn-moderate, ½-1 burn/spot size width apart
No. of burns— 1200-2000
Location and pattern—Same as for scatter/PRP laser in diabetic retinopathy.
57. FOLLOW UP SCHEDULE IN CRVO
Every month till regression of new vessels
1st follow up-1 month postlaser
• Undilated Slit-lamp examination and gonioscopy is a must to detect
regression of new vessels (NVI and NVA). After regression of new
vessels the follow up is carried out at 3 months interval.
59. PHOTOCOAGULATION IN RETINAL VASCULITIS
INDICATIONS
1. Eales’ disease—Mainly indicated
for ischemic and proliferative
stages (Stage II and III).
2. Other causes of retinal vasculitis:
• Pars planitis
• Sarcoidosis
• CMV retinitis
• Behcet’s disease.
CONTRAINDICATIONS
1. Presence of active inflammation,
i.e. phlebitis.
2. Stage I and IV of Eales’ disease.
60. TIMING OF LASER
Photocoagulation is done in Eales’ disease/retinal vasculitis only after the
inflammation subsides or is brought under control by oral steroid.
In Eales’ disease/retinal vasculitis photocoagulation can be delivered
through Slit-lamp biomicroscope/ Binocular indirect
ophthalmoscope/Endolaser.
61. PHOTOCOAGULATION TECHNIQUE
Technique of “Anchoring photocoagulation “ is employed to eliminate or lessen
complications.
Photocoagulation of new vessels around posterior pole.
PARAMETERS
Spot size - 200-300 μm
Intensity - Moderate to strong
Placement - Focal burns around the neovascular tissue along temporal arcade are
used. All neovascular extensions are similarly covered with focal photocoagulation
burns.
Additional sector PRP may be done prophylactically, if vitreous hemorrhage is
anticipated.
63. Formerly known as central serous retinopathy (CSR). Noninflammatory
in nature,Characterized by serous macular detachment. Defect(s) in the RPE
allows choroidal fluid to leak into the subretinal space.
Medical treatment has almost no role; in particular, corticosteroids have to
be strictly avoided as these may increase the risk of recurrence.
About 80% of eyes with CSCR undergo spontaneous resolution of
subretinal fluid and a return to normal or near normal visual acuity within 1-
6 months. Remaining 20% last longer but resolve within 12 months.
64. INDICATIONS FOR LASER
1. Persistent CSC of > 4-6 months duration.
2. Recurrent CSC with visual acuity < 6/12.
3. Chronic CSC.
4. Occupational need of the patient requires prompt recovery of vision.
5. Well-defined leaks > 500 μm away from the foveal center with a visual
acuity of < 6/12.
65. PHOTOCOAGULATION TECHNIQUE
Parameters
• Spot size-100-200 μm
• Exposure duration-0.1 sec
• Power—100-200 mW
• Intensity—Grade 2
• Pattern—3-5 confluent burns.
Follow up Schedule
1st – 2 weeks postlaser – OCT may
be considered.
2nd– Every 2 weeks post 1st
follow up.
68. RETINOPATHY OF PREMATURITY
ROP is characterized by proliferation of abnormal vessels in premature
infant’s peripheral retina.
Blinding sequelae of ROP can be prevented only by timely intervention in
infants at high-risk for progression.
The intervention includes proper and complete ablation of the avascular
retina by either cryoretinopexy or photocoagulation of all affected retinal
quadrants.
69.
70. LASERS FOR ROP
Indications
Threshold ROP (Stage 3, Zone 1 or
2, Extent 5 contiguous or 8
cumulative).
Timing of Laser
Within 24 to 48 hours of diagnosis.
Photocoagulation Technique Proper
Parameters
• Spot size—100 μm
• Exposure duration—0.1 sec
• Power—100 mW
• Intensity—Grade 2
71. Photocoagulation Technique Proper
Pattern: Nearly confluent or ½ burn width apart.
Photocoagulate the entire avascular area anterior to the mesenchymal ridge
upto the ora serrata.
Start with most posterior avascular zone and adjacent to most severe
pathological area.
Temporal area is treated at first.
Treat as many areas possible without indentation and minimal rotation of the
eyeball.
72. FOLLOW-UP SCHEDULE
1st – 1week-post laser
– Look for skipped areas
– Look for signs of regression
Flattening of mesenchymal ridge
Disappearance of mesenchymal
ridge
2nd – 2weeks-post laser
– Look for signs of regression (visible
within 2 weeks post laser)
– Retreatment may be considered in the
absence of signs of regression
– Treat skipped areas
• Every 2-4 weeks interval post regression of ROP.
75. INDICATIONS:
1. History of retinal detachment in
fellow eye
2. Morphological progression of
peripheral retinal degeneration.
3. Appearance of subjective
symptoms like lightning flashes.
4. Aphakic eye
CONTRAINDICATIONS
1. Asymptomatic lattice degeneration
without
a) Hole
b) History of RD in fellow eye
2. Presence of even a shallow RD around
peripheral retinal degeneration.
Peripheral retinal degenerations include lattice degeneration, paving stone
degeneration and pigmentary degeneration.
76. Photocoagulation technique
proper
PARAMETERS
Spot size – 500-800 µm
Exposure – 0.1-0.2 sec
Power: 400-600mW
Pattern: Usually solitary, linear,
single row and interrupted.
(interval = ½ spot size)
Photocoagulation burns should be
placed at least 1500 µm away from the
border of peripheral retinal
degeneration.
Anterior margins are photocoagulated
initially.
If degeneration is extensive – initial
single row of coagulation may be
reinforced by double row of linear
interrupted coagulation
77.
78. Retinal breaks
Retinal breaks include atrophic retinal holes (without operculum), retinal holes with
free floating or attached operculum and retinal tears.
INDICATIONS
History of RD in fellow eye
Very shallow RD with little SRF
Presence of vitreous traction on the
margin of break or operculum.
Presence of vitreous or PRH with a
break.
Persistent symptomatic retinal
break
CONTRAINDICATIONS
Asymptomatic inferior break with
pigmented margins.
Absence of history of RD in fellow
eye.
79. Photocoagulation technique proper
PARAMETERS
Spot size: 500 – 1000 µm.
Exposure: 0.2 – 0.5 sec
Power: 400 – 600 mW
Pattern: Usually solitary, linear, single
row and interrupted burns to surround
the anterior, posterior and lateral
margins of the break
The laser beam should avoid the pathway of
vitreous attachment to the operculum.
The operculum of horseshoe tear should not
be photocoagulated.
80. PHOTO DYNAMIC THERAPY
Subfoveal choroidal neovascularization (CNV) seen in wet or exudative Age-related Macular
Degeneration (AMD) is best treated by Photodynamic Therapy (PDT) or Ocular
Photodynamic Therapy (OPT) with verteporfin before the institution of anti-VEGF (Vascular
Endothelial Growth Factor) therapies.
Mode of Action
Verteporfin (Visudyne) is lipophilic (binds with LDL in the blood) and preferentially
accumulates in the capillary endothelial cells of neovascular membrane.
The accumulated dye absorbs specific wavelength (689 nm) of rays from laser emission.
The light activated verteporfin converts normal oxygen to ‘singlet oxygen’. The highly
energized ‘singlet oxygen’ and reactive free radicals destroy the endothelial cells of the CNV
leading to occlusion of the neovascular membrane without collateral damage to the overlying
photoreceptors.
82. PHOTO DYNAMIC THERAPY
INDICATIONS
1. Classic subfoveal CNV in Wet AMD
2. Idiopathic CNV
3. High myopia
4. Traumatic rupture of choroids
5. Ocular histoplasmosis syndrome
6. Angiod streaks
7. Drusen of the optic nerve
The size of the lesion should be ≤ 5400 μm
(microns) in its greatest linear dimension
CONTRAINDICATIONS
Ocular
1. Dry AMD
2. Size of the lesion ≥ 5400 μm (microns) in
its greatest linear dimension.
Systemic
1. Known hypersensitivity to verteporfin
2. Patients suffering from porphyria
3. Patients suffering from severe hepatic
disorder
Relative contraindications
• Uncontrolled hypertension
• Unstable cardiac disorder.
83. PHOTO DYNAMIC THERAPY
Fifteen minutes after commencement of verteporfin infusion, i.e. 5 minutes after conclusion of dye
infusion, the CNV is illuminated with light from diode laser (689 nm).
PARAMETERS
Spot size-500 μm
Size of the beam—The perfectly circular beam should cover the lesion entirely and is adjusted to
extend 500 μm beyond the margin of the CNV membrane. So, size of the beam = 1000 μm + Greatest
linear dimension of the lesion.
Exposure time-83 seconds
Intensity- 600 mW/cm²
Total laser Energy-50J/cm²
Dose of the Dye-6 mg/m²
Unlike thermal laser (photocoagulation), visible retinal changes are not seen during laser application
in PDT.
In bilateral cases, the other eye may be treated immediately.
84.
85. TRANSPUPILLARY THERMO THERAPY
Transpupillary ThermoTherapy (TTT) is an alternative to Photodynamic Therapy
(PDT) for treatment of subfoveal choroidal neovascular membrane (CNV)
secondary to wet AMD.
MODE OF ACTION
Intralesional marginal hyperthermia (max.10°C) occurs following exposure to
large spot size, low irradiance over longer period of time from diode laser (810
nm-Infrared).
This probably causes endothelial thrombosis and occlusion of the neovascular
membrane, through release of free radicals, without collateral damage to the
overlying photoreceptors.
86. TRANSPUPILLARY THERMO THERAPY
INDICATIONS
Occult subfoveal choroidal neovascular
membrane (CNV) in Wet AMD
Occult juxtafoveal choroidal neovascular
membrane (CNV) in Wet AMD
Retinoblastoma
Choroidal hemangioma
Choroidal melanoma.
CONTRAINDICATIONS
Dry AMD
Choroidal neovascular membrane
(CNV) within 200 μm of the optic
disc.
Subfoveal choroidal neovascular
membrane (CNV) with good visual
acuity
87. TTT Technique proper
TranspupillaryThermoTherapy (TTT) is done within 72 hours post recent FFA.
The CNV is illuminated with light from diode laser (810 nm). The perfectly circular beam
should cover the lesion entirely.
PARAMETERS
Spot size-0.8 mm/1.2 mm/2 mm/3 mm
Exposure time-60 seconds (fixed)
Power-200- 600 mW. It is titrated by placing a test burn in nasal retina. Absence of reaction
or minimal reaction at the level of the RPE indicates optimum power requirement.
The power also depends on the spot size. Smaller spot size requires less power. Indian eyes
being more pigmented (contains more melanin pigments) require less power in comparison
to European /Caucasian eyes.
88. TTT is delivered through a slit lamp using infrared diode laser at 810 nm
