2. What is Laser?
L : Light
A: Amplification (by)
S: Stimulated
E : Emission (of)
R : Radiation
Term coined by Gordon Gould.
Lase means to absorb energy in one form and to emit a new
form of light energy which is more useful.
6. The concept of ocular therapy using light first was
publicized by Meyer-Schwickerath, who took patients to
the roof of his laboratory in 1949 and focused sunlight on
their retinas to treat melanomas.
But,…required sunny weather
Thus, nonsolar sources.
Carbon arcs were used; by the mid-1950s, the xenon arc
photocoagulator had been developed and was made
commercially available by Zeiss.
BUT,…Strong visible and infrared emission leads to intense
retinal burn
7. A MASER (microwave amplification by stimulated emission of radiation)
is a device that produces coherent electromagnetic waves through
amplification by stimulated emission.
The first maser was built by Charles H. Townes, James P. Gordon, and H.
J. Zeiger at Columbia University in 1953
8. 1960 - Theodore Maiman : Built first laser
by using a ruby crystal medium .
9. 1963 - C. Zweng: First medical laser
trial (retinal coagulation).
1965 - W.Z. Yarn: First clinical laser
surgery.
1970- The excimer laser was invented
in by Nikolai Basov
1971 -Neodymium yttrium aluminum
garnet
(Nd.YAG) and Krypton laser
developed.
1983 : Trokel developed the eximer
laser.
10. PROPERTIES OF LASER LIGHT
Monochromatic (emit only one wave length)
Coherence (all in same phase-improve focusing )
Polarized (in one plane-easy to pass through media)
Collimated (in one direction & non spreading )
High energy (Intensity measured by Watt J/s)
11. LASER Vs. LIGHT
LASER
Simulated emission
Monochromatic.
Highly energized
Parallelism
Coherence
Can be sharply
focussed.
LIGHT
Spontaneous
emission.
Polychromatic.
Poorly energized.
Highly divergence
Not coherent
Can not be sharply
focussed.
12. How LASER is produced ?
Light is a form of energy at which the human eye is sensitive
13. LASER PHYSICS
Light as electromagnetic waves, emitting radiant energy
in tiny package called ‘quanta’/photon. Each photon has
a characteristic frequency and its energy is proportional
to its frequency.
Three basic ways for photons and atoms to interact:
Absorption
Spontaneous Emission
Stimulated Emission
23. THREE TYPE OF OCULAR PIGMENT
Haemoglobin:
absorbs blue, green and yellow with minimal red wavelength
absorption,
Argon Green are absorbed , Krypton yellow. useful to
coagulate the blood vessels.
Xanthophyll:
Macular area, Lens
Maximum absorption is blue. minimally absorbs yellow or red
wavelengths. Argon blue is not recommended to treat
macular lesions.
Melanin:
RPE, Choroid
absorbs green, yellow, red and infrared wavelengths
Pan Retinal Photocoagulation, and Destruction of RPE
Effective retinal photocoagulation depends on how well light penetrates the
ocular media and how well the light is absorbed by pigment in the target tissue
25. Thermal Effects
(1) Photocoagulation:
Laser Light
Target Tissue
Generate Heat
Denatures Proteins
(Coagulation)
Rise in temperature of about 10 to 20 0C will cause coagulation of tissue.
26. How does panretinal photocoagulation
work?
Sublethally injured RPE cells that surround areas of
photocoagulation necrosis and produces significant
thinning of the outer retina.
By decreasing the oxygen consumption at the
photoreceptor–RPE complex, more oxygen is available to
diffuse into the inner retina and vitreous.
Enhanced oxygen diffusion into the inner retina and
vitreous reduces inner retina ischemia and the stimulus
for neovascularization.
PRP reduces retinal ischemia and the hypoxia-induced
expression of VEGF.
28. Thermal Effects
(3)Photovaporization
Vaporization of tissue to CO2 and water occurs when
its temperature rise 60—100 0C or greater.
Commonly used CO2
Absorbed by water of cells
Visible vapor (vaporization)
Heat Cell disintegration
Cauterization Incision eg..Femtosecond laser
29. Photochemical effcts
Photoablation:
Breaks the chemical bonds that hold tissue together
essentially vaporizing the tissue, e.g. Photorefractive
Keratectomy, Argon Fluoride (ArF) Excimer Laser.
Usually -
Visible Wavelength: Photocoagulation
Ultraviolet Yields : Photoablation
Infrared : Photodisruption
Photocoagulation
Contd. …
30. PHOTOCHEMICAL EFFECT
Photoradiation (PDT):
Also called photodynamic therapy.
E.G. Treatment of Ocular tumours and CNV
Photon + Photo sensitizer in ground state (S)
Molecular Oxygen Free Radical
S + O2 (singlet oxygen) Cytotoxic Intermediate
Cell Damage, Vascular Damage , Immunologic Damage
31. Delivery systems
Transpupillary: - Slit lamp
- Laser Indirect Ophthalmoscopy
Trans scleral : - Contact
- Non contact
Endophotocoagulation.
32. Slit lamp biomicroscopic laser
delivery
Most commonly employed mode for anterior and
posterior segment.
ADVANTAGES:
Binocular and stereoscopic view.
Fixed distance.
Standardization of spot size is more accurate.
Aiming accuracy is good.
33. Laser indirect ophthalmoscope.
Advantages :
Wider field(ability to reach periphery).
Better visualization and laser application in hazy
medium.
Ability to treat in supine position.(ROP/EUA)
Disadvantage : difficulty in focusing.
Difficulty to standardize spot size.
Expensive.
Un co-operative patient.
Learning curve.
39. Uses
1. Diabetic Retinopathy – Pan-retinal
photocoagulation.
Indications:
High risk PDR
Early PDR or very severe NPDR in
→ Patients with poor compliance
→ During pregnancy
→ Patients with systemic diseases
→ Pending cataract surgery
→ One-eyed patients
40. Type of laser: PRP with Argon (green-514nm
wavelength)
Laser delivery system: Indirect ophthalmoscope and +20
D lens
Laser parameters:
ꟷ Spot size: 200-500 μ
ꟷ Pulse duration: 100 ms
ꟷ Power: 200-250 mW (goal is to produce grey burn)
ꟷ Spacing: 1-1.5 burn width apart
41. Number of sittings: 3
ꟷ PRP I: Inferior and nasal retina
ꟷ PRP II: Temporal retina
ꟷ PRP III: Superior retina
43. 2. Diabetic maculopathy:
Indication: Clinically significant macular edema
Basic guidelines
ꟷ All areas of macular thickening must be treated
ꟷ FFA is done to look for points of leakage
ꟷ Focal leak → focal laser photocoagulation
ꟷ Diffuse leak → grid photocoagulation
Laser delivery system: Slit lamp
44. Focal laser
Direct laser to microaneurysm
>500 μm from centre of fovea
Laser parameters:
ꟷ Spot size: 50-100 μ
ꟷ Duration: 50-100 ms
ꟷ Power- titrated to whiten
microaneurysm
Grid laser
Laser to area of diffuse leakage &
capillary non-perfusion on FFA
Laser parameters:
ꟷ Spot size: 50-200 μ
ꟷ Duration: 50-100 ms
ꟷ Power: titrated to achieve mild
burn
ꟷ Laser is done in C-shaped manner
within the vascular arcade &
avoiding area of papillomacular
bundle
46. Type of laser:Grid laser- for macular
edema
Laser parameters:
ꟷ Spot size: 50-200 μm
ꟷ Duration: 50-100 ms
ꟷ Power: titrated to achieve mild
burn
Sectoral photocoagulation-
for neovacularization
Laser parameters
ꟷ Spot size: 200-500 μm
ꟷ Pulse duration: 100 ms
ꟷ Power: 200-250 mW
ꟷ Area: beyond 2 DD from centre of
macula upto equator
47. 4. Retinopathy of prematurity
Indications:
ꟷ Stage I, Zone I with plus disease
ꟷ Stage II, Zone I with plus disease
ꟷ Stage III, Zone I with plus disease
ꟷ Stage III, Zone I without plus disease
ꟷ Stage II, Zone II with plus disease
ꟷ Stage III, Zone II with plus disease
Type of laser: PRP (with LIO)
48. Laser parameters:
ꟷ Spot size:200-500 μm
ꟷ Power: 300-400 mW
ꟷ Duration: 300-400 ms
ꟷ Aim is to ablate the entire avascular retina from the
ridge upto the ora serrata in a near confluent burn
pattern getting as close to the ridge as possible.
49. Complications:
ꟷ Premature infants are prone to develop apnoea.
ꟷ Conjunctival chemosis.
ꟷ Subconjunctival hemorrhage due to excessive scleral
indentation.
ꟷ Rarely cataract formation.
ꟷ Intense photocoagulation may lead to anterior
segment ischemia and necrosis resulting in hypotony
and phthisis bulbi.
50. 5. Choroidal neovascularization (CNV)
Conventional(direct) laser:
Type of laser: 532 nm frequency doubled YAG or
argon green (514 nm)
Technique:
ꟷ The membrane is first delimited by moderate
intensity non-confluent laser spots extending to at
least 100 μ of the surrounding normal retina
Subsequently, intense confluent burns are applied to
the membrane per se until uniform whitening is
observed
51.
52. Laser parameters
ꟷ Extrafoveal
Characteristi
cs
Border Membrane Treatment area
Spot size 100-200 μ 200 μ 100 μ beyond
hyperfluorescenc
e on FFA
Duration 100-200
ms
200-500 ms
Intensity Moderate Intense
53. ꟷ Juxtafoveal
Characteristics Border Membran
e
Treatment area
Spot size 200 μ 200 μ Confined to
hyperfluorescenc
e on FFA
Duration 200-500
ms
200-500
ms
Intensity Moderate Intense
55. Photodynamic therapy:
ꟷ Dosage: 6 mg/m2 of verteporfin infused intravenously
ꟷ The amount of dye calculated is given over 10 minutes
(infusion phase) and then a further 5 minutes are allowed
for the dye to accumulate (accumulation phase).
ꟷ After this 15 minute interval, the choroidal membrane
complex is exposed to low energy diode laser light (689
nm) for 83 seconds.
56. ꟷ This activates the dye accumulated with the
neovascular complex and results in its closure.
ꟷ Spot size is 1000 more than the greatest linear
dimension (GLD) of the choroidal membrane
identified in the early angiographic frame (for classic
membranes)
Complications:
ꟷ Visual disturbances
ꟷ Photosensitivity reactions
ꟷ Overdosing- macular infarction
ꟷ In case of extravasation- backache and allergic
reactions
57. Transpupillary Thermotherapy:
Advantage over conventional laser: Compared to the
40⁰ temperature elevation with conventional laser
photocoagulation, TTT causes a 10⁰ rise of temperature,
so minimizing collateral damage
Type of laser: Slit lamp with a modified diode(810nm)
laser
Laser patameters
Initial treatment
ꟷ Spot size: 3mm
ꟷ Duration: 60 s
ꟷ Power: 800mW
58. ꟷ If a change in colour of retina is noted, then the
power is reduced by 20% until no colour change is
seen for entire 60 sec duration.
Transscleral Diode Laser Photocoagulation
Procedure:
ꟷ Under aseptic conditions and peribulbar anesthesia
ꟷ Lateral rectus muscle bridled after doing a limited
peritomy temporally
ꟷ Intermuscular septa on either side dissected and then
the diopexy probe was introduced
59. ꟷ Test burns are applied to the temporal retina and the
time taken to obtain a visible burn noted
ꟷ The probe is then gently guided to the submacular
area under indirect ophthalmoscopy
ꟷ Control burn is applied to the region of the membrane
as determined by site of leakage seen on early phase
of FFA
ꟷ Conjunctiva closed with 6-0 vicryl interrupted sutures
ꟷ Subconjunctival gentamicin plus dexamethasone
injection given.
60. 6. Retinal lesions predisposing to detachment and
retinal tear
Indications:
ꟷ Presence of symptoms- Floaters, flashes and blurring
of vision.
ꟷ Focal vitreo-retinal adhesions
ꟷ Presence of non-traumatic retinal detachment in
fellow eye
ꟷ Large tear(>2 DD), posterior tear, superior tear, U-
shaped or flap tear
ꟷ Family history of retinal detachment
61. Purpose: To induce a sterile inflammation which
stimulate proliferation of the RPE → indirectly
improves adhesion between the RPE and the
neurosensory retina.
Laser delivery system: Slit lamp with contact lens or
LIO
Principle:
ꟷ The entire perimeter of the break should be
surrounded by laser application.
ꟷ Particular attention to the anterior margin and horns
of a tear should be paid.
62. ꟷ In the presence of a rim of fluid or in subclinical
detachment, laser is applied to the attached retina
immediately around the detachment.
ꟷ If applied to the area of detachment, it may cause
further progression of the detachment.
ꟷ Laser treatment of an inflamed retina is avoided as
there is a risk of producing a retinal break
Laser parameters:
ꟷ Two-three rows of confluent burns
ꟷ Spot size: 200-500 μm
ꟷ Mild to moderate burn intensity
63. 7. Eales’ disease: It is an idiopathic, inflammatory
peripheral vasculitis characterised by retinal
periphlebitis and capillary non-perfusion leading to
hypoxia
Indications:
ꟷ Neovascularization elsewhere
ꟷ Neovascularization disc
ꟷ Neovascularization iris
Laser delivery system: LIO
65. 8. Central serous chorioretinopathy
Focal laser photocoagulation (extra-foveal leakage)
Indications:
ꟷ Non-resolving or recurrent CSCR with V/A: <6/12
ꟷ Well defined leakage on FFA, atleast 500 μ away
from centre of fovea
Laser parameters:
ꟷ Spot size: 100- 200 μ
ꟷ Duration: 100-200 ms
ꟷ Power: 100-200 mW
66. Photo dynamic therapy (PDT)- foveal leakage
Standard/conventional PDT
Dose: 6mg/m2 infusion of
vertiporfin over 15 min followed
by delivery of laser 692nm 15 min
after commencement of infusion
Total light energy: 50J/cm2,
delivered in 83 sec
(photosensitisation time)
Complications:
ꟷ CNV development
ꟷ Post-treatment visual loss
ꟷ Potential choroidal ischaemia
Safety enhanced PDT
Dose: 3mg/m2 infusion of
vertiporfin over 8 min followed by
delivery of laser 692nm 10 min
after commencement of infusion
Total light energy: 50J/cm2,
delivered in 83 sec
(photosensitisation time)
67. 9. Retinal artery macroaneurym:
These are solitary, saccular or fusiform dilation
(diameter:125 -250μ) of the retinal arteriole involving
usually, the first three divisions.
Two forms: acute & chronic
Acute form: sudden loss of vision due to retinal or
vitreous hemorrhage
Chronic form: gradual loss of vision due to leakage
and exudation into the macular area
Laser photocoagulation is required for chronic forms
68. Laser parameters:
ꟷ Spot size: 200-300 μ
ꟷ Duration: 200-500 ms
ꟷ Power: 200mW
Direct treatment: laser is focused directly on the
macroaneurysm so as to obtain slow and gentle
whitening
In indirect treatment: laser burns are placed around
the aneurysm
69. 10. Coats’ disease: Idiopathic retinal telangiectasia
associated with intraretinal and subretinal exudation
and frequently exudative retinal detachment, without
signs of vitreoretinal traction
Indication:
ꟷ Severe vascular anomalies with macular exudation
ꟷ Exudative retinal detachment
ꟷ Vascular anomalies posterior to equator
ꟷ Neovascularization
Type of laser: LIO/ Slit lamp
70. Laser parameters:
ꟷ Spot size: 200-500 μ
ꟷ Power: 200 mW
ꟷ Duration: 200-500 ms
ꟷ End point: whitening of lesion
71. 11. Retinal capillary hemangioma: Vascular hamartoma
Indication:
ꟷ All capillary hemangiomas except those touching the
optic nerve head
Type of laser: Argon green or frequency doubled YAG
Laser parameters:
ꟷ Spot size: 200-500 μ
ꟷ Duration: 0.2- 1.0 s
ꟷ Power: titred to produce mild-moderate whitening of
lesion.
ꟷ Small lesion→ direct treatment
ꟷ Large lesion → treatment of feeder vessel
72. 12. Choroidal hemangioma: Vascular hamartoma
Manifest in two forms: diffuse & circumscribed
Indication:
ꟷ Serous retinal detachment
Aim of treatment: achieve resolutioon of serous
retinal detachment and not tumor obliteration
Conventional laser: entire tumor surface is covered
with laser spots
73. PDT: 6 mg/m2 of verteporfin dye is injected
intravenously
Laser parameters
ꟷ Spot size: 6000 μ(maximum)
ꟷ Laser used 689 nm
ꟷ Type of laser delivery: Slit lamp
ꟷ Lens used: Mainster wide field lens
ꟷ In peripapillary choroidal hemangioma, laser spot is
applied at a distance of 200 μ from the optic disc edge
ꟷ Large lesion(>2 mm) radiant exposure of 100 J/cm2
with exposure of 186 seconds
ꟷ Small lesion(<2 mm) radiant exposure of 75 J/cm2
with exposure of 125 seconds
74. 13. Choroidal melanoma: commonest primary
malignant intraocular tumors, arising from choroidal
melanocytes.
Indication:
ꟷ Tumor size: <15 mm basal diameter &
thickness <5mm
Type of laser: Argon laser photocoagulation
76. Type of laser: Slit lamp
Technique:
ꟷ The cone angle is set at 10⁰ and laser energy is
focused above the inferior extent of the haemorrhage
to facilitate gravity-aided drainage of blood into the
vitreous cavity
ꟷ Begin with an energy of 1.5 mJ using single pulse.
ꟷ 5-6 spots required to create a dehiscence and
ꟷ 8-10 spots of lower energy to achieve drainage of the
blood.
81. Advantages:
ꟷ Safe
ꟷ Relatively painless
ꟷ Less time consuming
ꟷ Well tolerated
ꟷ More number of spots in single sitting
ꟷ Requires less number of sitting
82. 2. Navigational lasers
532-nm pattern-type eye-tracking laser integrates live
colour fundus imaging, red-free and infra-red
imaging, FFA with photocoagulator system.
After image acquisition and making customized
treatment plans by physicians including marking
areas which will be coagulated the treatment plan is
superimposed onto the live digital retina image during
treatment
The physician controls laser application and the
systems assist with prepositioning the laser beam.
83. Advantages over conventional lasers:
ꟷ Fast
ꟷ Painless
ꟷ Better documentation
ꟷ Wide field viewing system allows for better accuracy
84. Scanning Laser ophthalmoscopy
SLO uses a near-infrared diode laser (675 nm) beam
that rapidly scans the posterior pole
The reflected light is detected by a confocal photodiode
that is conjugate to the retinal plane, and the digitized
image is stored in a computer.
The confocal filter ensures that only light reflected from
the narrow spot illuminated by the laser is recorded.
85. Stereoscopic high-contrast images can be produced
with and without dyes such as fluorescein or ICG,
and altering the laser wavelength permits selective
examination of different tissue depths
Clinically, however, SLO has been used more in the
objective evaluation of the surface contour of the
optic nerve head in glaucoma than in the diagnosis of
retinal disease.
86. Optical coherence tomography(OCT)
Uses diode laser light in the near infrared spectrum (810
nm) to produce high resolution cross-sectional images
of the retina using coherence inferometry
Editor's Notes
The two photons that have been produced can then generate more photons, and the 4 generated can generate 16 etc… etc… which could result in a cascade of intense monochromatic radiation.