Retinal lasers are used to treat various retinal conditions by using light energy to coagulate tissues. Different types of lasers are used depending on the condition and location being treated. Lasers work through thermal effects like photocoagulation or photodisruption, or photochemical effects like photoradiation. Common uses include treating diabetic retinopathy with panretinal photocoagulation, diabetic macular edema with focal or grid laser, and retinal vein occlusion or choroidal neovascularization with grid laser. Precise laser parameters are used depending on the target tissue and desired effect.
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.
5. 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
6. 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
7. 1960 - Theodore Maiman : Built first laser by
using a ruby crystal medium .
8. 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.
9. 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)
10. 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
16. 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
18. 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.
19. 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.
21. 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
22. 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. …
23. 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
24. Delivery systems
Transpupillary: - Slit lamp
- Laser Indirect Ophthalmoscopy
Trans scleral : - Contact
- Non contact
Endophotocoagulation.
25. 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.
26. 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.
32. 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
33. 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
34. Number of sittings: 3
ꟷ PRP I: Inferior and nasal retina
ꟷ PRP II: Temporal retina
ꟷ PRP III: Superior retina
36. 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
37. 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
39. 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
40. 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)
41. 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.
42. 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.
43. 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
44.
45. 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
46. 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
48. 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.
49. 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
50. 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 parameters
Initial treatment
ꟷ Spot size: 3mm
ꟷ Duration: 60 s
ꟷ Power: 800mW
51. 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
52. 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.
53. 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
54. 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.
55. 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
56. 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, Slit lamp
58. 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
59. 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)
60. 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
61. 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
62. 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
63. Laser parameters:
ꟷ Spot size: 200-500 μ
ꟷ Power: 200 mW
ꟷ Duration: 200-500 ms
ꟷ End point: whitening of lesion
64. 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: titreted to produce mild-moderate whitening of lesion.
ꟷ Small lesion→ direct treatment
ꟷ Large lesion → treatment of feeder vessel
65. 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
66. 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
67. 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
69. 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.
74. 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
75. 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.
76. Advantages over conventional lasers:
ꟷ Fast
ꟷ Painless
ꟷ Better documentation
ꟷ Wide field viewing system allows for better accuracy
77. Sub-threshold micropulse laser
The familiar "grayish" endpoint of conventional threshold
photocoagulation is typically associated with thermal elevations of
20-30°C, which cause coagulation necrosis and characterize the
treatment as a supra-threshold photocoagulation.
The spreading and decaying thermal wave inevitably reaches the
tissues surrounding the burn and this causes the laser burn to
expand.
Using a micropulse mode, laser energy is delivered with a train of
repetitive short pulses (typically 100 to 300 microseconds “on”
and 1700 to 1900 microseconds “off”) within an “envelope” whose
width is typically 200 to 300 milliseconds.
Micropulse power as low as 10% to 25% of the visible threshold
power has been demonstrated to be sufficient to show consistent
RPE-confined photothermal effect with sparing of the
neurosensory retina on light and electron microscopy.
78. Sub-threshold micropulse laser
Tissue-sparing protocols are designed to produce only
subtle thermal elevations with effects that are invisible
during treatment and remain so thereafter.
The inner retinal temperature must remain below the
threshold of coagulative damage for the retina to
maintain its natural transparency.
79. Sub-threshold micropulse laser
Lower energy per pulse reduces peak power, lowers the
risk of hemorrhage, decreases the temperature buildup
per pulse, and ultimately results in improved confinement
of photothermal effects.
Absence of chorioretinal laser damage may permit high-
density therapy with confluent applications over the
entire edematous area and retreatment of the same
areas.
This may be particularly useful for the as-needed
treatment of macular edema.
80. Subthreshold micropulse laser therapy
with yellow (577 nm) laser
Now, it is possible to deliver a subthreshold micropulse laser that is
above the threshold of biochemical effect but below the threshold of
a visible, destructive lesion thereby preventing collateral damage.
The 577 nm wavelength occurs outside the absorption spectrum of
retinal xanthophylls, potentially allowing for treatment close to the
fovea.
81. Subthreshold micropulse laser therapy
with yellow (577 nm) laser
It also has the highest oxyhaemoglobin to melanin absorption ratio
and therefore, is the most effective laser for vascular structures.
The combined absorption by both melanin and oxyhemoglobin of
577 nm causes lesser scatter compared to 532 nm or other yellow
wavelengths (561/568 nm).
This leads to energy concentration to a smaller volume allowing
use of lower powers and shorter pulse durations.
Hinweis der Redaktion
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.