Laser in ophthalmology

Retinal Laser
DR. PRATIK MOHOD

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.

LASER history
 1917 -Sir Albert Einstein created the foundations for the laser.

“
”
Concept of laser/light sources
in ophthalmology came
from????????

 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

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

1960 - Theodore Maiman : Built first laser
by using a ruby crystal medium .

 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.

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)

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.

How LASER is produced ?
Light is a form of energy at which the human eye is sensitive

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

CLASSIFICATION OF LASER
 Solid State
Ruby
Nd.Yag
Erbium.YAG
 Gas
Ion
Argon
Krypton
He-Neon
CO2
 Metal Vapour
Cu
Gold
 Dye
Rhodamine
 Excimer
Argon Fluoride
Krypton Fluoride
Krypton Chloride
 Diode
Gallium-Aluminum Arsenide
(GaAlAs)

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

LASER TISSUE INTERACTION
LASER
TISSUE
Thermal Effect Photo-
chemical
Ionizing
Effect
 Photocoagulation  Photoradation
 Photodisruption  Photoablation
 Photovaporization

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.

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.

Thermal Effects
(2) Photodisruption:
 Mechanical Effect: Laser Light

Acoustic Shockwaves

Tissue Damage
Contd. …

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

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. …

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

Delivery systems
 Transpupillary: - Slit lamp
- Laser Indirect Ophthalmoscopy
 Trans scleral : - Contact
- Non contact
 Endophotocoagulation.

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.

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.

Retinal lasers- Types and
uses

Lens Uses Image Spot
magnificatio
n
Field of view
Goldmann Macula
Equator
Periphery
Virtual
Erect
1.08 36⁰
Volk Supermacula
2.0
Macula Real
Inverted
2.15 70⁰
Mainster High
magnification
Macula Real
Inverted
1.34 75⁰
Volk area
centralis
Macula
Equator
Real
Inverted
1.13 82⁰
Mainster Standard Macula
Equator
Real
Inverted
1.03 90⁰
Panfundoscopic Equator
Periphery
Real
Inverted
0.76 120⁰

Lens Uses Image Spot
magnification
Field of view
Volk
transequator
Equator
Periphery
Real
Inverted
0.75 122⁰
Mainster wide
field
Equator
Periphery
Real
Inverted
0.73 125⁰
Volk Quadr
Aspheric
Equator
Periphery
Real
Inverted
0.56 130⁰
Mainster Ultra
field PRP
Equator
Periphery
Real
Inverted
0.57 140⁰
Volk
SuperQuard
160
Equator
Periphery
Real
Inverted
0.56 160⁰

Uses- Therapeutic
1. Diabetic retinopathy
2. Diabetic maculopathy
3. Retinal vein occlusion
4. Retinopathy of prematurity
5. Choroidal neovascularization (CNV)
6. Retinal lesions predisposing to detachment and retinal tear
7. Eales’ disease
8. Central serous chorioretinopathy
9. Retinal artery macroaneurym
10. Coats’ disease
11. Retinal capillary hemangioma
12. Choroidal hemangioma
13. Choroidal melanoma
14. YAG Laser hyaloidotomy
15. Optic disc pit

Uses- Diagnostic
1. Scanning laser ophthalmoscopy
2. Optical coherence tomography

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

 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

 Number of sittings: 3
ꟷ PRP I: Inferior and nasal retina
ꟷ PRP II: Temporal retina
ꟷ PRP III: Superior retina

 Complications
ꟷ Transient: headache, blurring of vision, macular
edema
ꟷ Persistent: nyctalopia, accomodative defect, reduced
contrast sensitivity, photophobia, reduced visual
fields
ꟷ PVD induction
ꟷ Inadvertent foveal burns

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

Focal laser
 Direct laser to microaneurysm
>500 μm from centre of fovea
ꟷ Duration: 50-100 ms
ꟷ Power- titrated to whiten
microaneurysm
Grid laser
 Laser to area of diffuse leakage &
capillary non-perfusion on FFA
ꟷ Power: titrated to achieve mild
burn
ꟷ Laser is done in C-shaped manner
within the vascular arcade &
avoiding area of papillomacular
bundle

3. Retinal vein occlusion
 Indication:
ꟷ Macular edema
ꟷ V/A: <20/40 (after 3 months)
ꟷ Large segment of capillary non-perfusion(>5 DD)
ꟷ Neovascularization
 Contraindication:
ꟷ Macular ischemia

Type of laser:Grid laser- for macular
edema
Laser parameters:
ꟷ Spot size: 50-200 μm
ꟷ Power: titrated to achieve mild
burn
Sectoral photocoagulation-
for neovacularization
Laser parameters
ꟷ Power: 200-250 mW
ꟷ Area: beyond 2 DD from centre of
macula upto equator

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)

ꟷ Spot size:200-500 μm
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.

 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.

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

 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

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

ꟷ Subfoveal
Characteristic
s
Border Membrane Treatment area
Spot size 200 μ 200 μ Confined to
hyperfluorescenc
e on FFA
Duration 200 ms 200-500 ms
Intensity Intense Intense

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.

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

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

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

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.

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

 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.

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
ꟷ Two-three rows of confluent burns
ꟷ Mild to moderate burn intensity

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

 NVD→ PRP
 Single NVE → sectoral scatter photocoagulatio
 NVI → PRP
 Laser parameter:

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
ꟷ Spot size: 100- 200 μ

 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)

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

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

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

ꟷ Power: 200 mW
ꟷ End point: whitening of lesion

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
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

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

 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

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

14. YAG Laser hyloidotomy:
 Indications:
ꟷ Premacular haemorrhage secondary to diabetic
retinopathy, aplastic anemia, Terson’s syndrome,
Valsalva retinopathy, vasculitis, ruptured retinal artery
macroaneurysm, retinal vascular occlusions
ꟷ Persistent premacular haemorrhage beyond 4 weeks
ꟷ Size of harmorrhage: >3 DD
ꟷ Absence of retinal proliferation(If present PRP is
done first)

 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.

 Complications:
ꟷ Non-resolving vitreous haemorrhage
ꟷ Creation of retinal holes
ꟷ Retinal detachment

15. Optic disc pit:
 Indication:
ꟷ Associated serous macular detachment
 Laser photocoagulation along the temporal margin of
optic disc.

Recent advances
1. PASCAL(Pattern scanning laser)
 Semi-automated laser delivering device
 Allows for a pattern of 4-56 burns to be applied in <1 sec
using a scanning laser with shorter pulse duration
 Indicactions:
ꟷ Diabetic retinopathy(PDR &NPDR)
ꟷ Choroidal neovascularization(CNVM & SRNVM)
ꟷ Age-related macular degeneration
ꟷ Retinal vein occlusion(BRVO &CRVO)
ꟷ Retinal tear, holes
ꟷ Retinal detachment

 Laser source: Nd:YAG laser
 Delivery system: Slit lamp or LIO
 Laser parameters
ꟷ Spot size: 200 μ
ꟷ Duration: 20 ms

 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

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.

 Advantages over conventional lasers:
ꟷ Fast
ꟷ Painless
ꟷ Better documentation
ꟷ Wide field viewing system allows for better accuracy

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.

 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.

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

Laser in ophthalmology

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