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BASICS OF PAN RETINAL, SECTOR AND FOCAL RETINAL LASER PHOTOCOAGULATION.pptx
1. BASICS OF PAN RETINAL AND FOCAL
RETINAL LASER PHOTOCOAGULATION
PRESENTED
BY
DR. AVURU CHUKWUNALU JAMES
29/03/2023
2. OUTLINE
• INTRODUCTION
• DEFINITION, PROPERTIES AND CLASSIFICATION OF LASER
• USES OF LASERS
• RETINAL PHOTOCOAGULATION
• LASER DELIVERY SYSTEMS
• PROCEDURE/ TECHNIQUES OF LASER ADMINISTRATION
• LASERS IN GENERAL ANSD SPECIFIC CASES
• RECENT ADVANCES IN RETINAL LASER PHOTOCOAGULATION
• COMPLICATIONS OF LASER
• CONCLUSION
3. INTRODUCTION
• LASER’ is an acronym for “Light Amplification by the Stimulated
Emission of Radiation.”
• Describes the emission process by which an intense beam of
electromagnetic radiation is generated
• When energy from laser is absorbed by the retinal pigment epithelium
(RPE), it is converted into thermal energy.
• Coagulation necrosis occurs with denaturation of cellular proteins as
temperature rises above 65°C.
4. PROPERTIES OF LASER
• Monochromatic; one wavelength
• Collimated; all photons run parallel & focused to a
small point
• Coherent; always in same phase
• Highest possible speed
5. THREE BASIC WAYS FOR PHOTONS AND ATOMS TO
INTERACT:
• Absorption
• Spontaneous Emission
• Stimulated Emission
6. PHYSICS OF LASER
• Some substances have property to absorb energy in one
form & emit a new form of energy.
• These substances are lasing in nature and obey Bohr’s
theory.
• On pumping these lasing substances, electrons are
transfered from a lower orbit to higher orbit
• Excited atoms in turn decay back to their original orbit of
lower energy, emitting photons i.e packets of energy.
7. LASER SYSTEM AND MEDIA
• The lasering medium is contained in an optical
cavity (resonator) with mirrors at both ends.
• Reflect the light in the cavity and thereby
circulate the photons through the lasing material
multiple times to efficiently stimulate emission
of radiation from excited atoms.
• One of the mirrors is partially transmitting,
thereby allowing a fraction of the laser beam to
emerge.
8. CLASSIFICATION OF LASING MEDIUM
• The lasing medium can be
Solid, Liquid or Gas
• Lasers can be pumped by
continuous discharge lamps
and by pulsed flash lamps.
9. RETINAL LASER THERAPEUTIC USES
• Central serous chorioretinopathy
• Retinal artery macroaneurym
• Coats’ disease
• Retinal capillary hemangioma
• Choroidal hemangioma
• Choroidal melanoma
• YAG Laser hyaloidotomy
• Optic disc pit
• Most of the uses are now obsolete or 2nd line
tx due to the advent of anti-VEGF
• Diabetic retinopathy
• Diabetic maculopathy
• Retinal vein occlusion
• Retinopathy of prematurity
• Choroidal neovascularization (CNV)
• Retinal lesions predisposing to detachment
and retinal
• Eales’ disease
10. PHOTOCOAGULATION (PHC) BY LASERS
• It is a photothermal reaction
• Absorption of light by the target
tissue results in a temperature rise of
20 to 30 deg C
• Causes denaturization of proteins
• This process is Pigment dependent
• Typical lasers with
photocoagulation effect
• Argon,
• Krypton dye,
• Diode(810nm)
• Frequency double Nd:Yag
11. RETINA PHC LASER TYPES IN RETINA-ARGON BLUE-
GREEN LASER
• 70% blue (488 nm) and 30%
green(514nm)
• Absorbed selectively at retinal pigment
epithelial layer (RPE), hemoglobin
pigments, choriocapillaries, inner and
outer nuclear layer of the retina.
• It coagulates tissues between the
choriocapillaris and inner nuclear layer.
• Main adverse effects: high intraocular scattering,
macular damage in photocoagulation near the fovea,
and choroidal neovascularization (if Bruch's
membrane is ruptured).
12. RETINA PHC LASER TYPES CONTD
• Frequency-doubled Nd-YAG Laser
(532 nm):
• Highly absorbed by hemoglobin,
melanin in retinal pigment epithelium
and trabecular meshwork.
• can be used either continuously or in
pulsed mode.
• PASCAL (Pattern Scan Laser) is one
such type of laser types
• Krypton red (647 nm)
• Well absorbed by melanin
• can pass through hemoglobin
• Suitable for treatment of subretinal neovascular membrane.
• Has low intraocular scattering with good penetration
through media opacity or edematous retina
• Has ability to coagulate the choriocapillaries and the
choroid.
13. RETINA PHC LASER TYPES CONTD
• Diode laser (805-810 nm):
• It is well absorbed by melanin.
• Has near to infrared spectrum (near
invisible) which makes it more
comfortable to use due to absence of
flashes of light.
• Has deep penetration through the retina
and choroid
• Laser of choice in treatment of Retinopathy of Prematurity
(ROP) and some types of retina lesions.
• Also used via trans-scleral route to treat the ciliary body
14. TISSUE EFFECTS OF PHC
• MOA : Increases the temp from
37 to 50 degrees
• conformational changes,
• Enzyme inactivation
• Loss of structural integrity
• Cell necrosis
• Haemostasis and coagulation
• Induces moderate sterile
inflammation which creats
Creates bio adhesion
• Collagen shrinkage; usually
beneficial
• Membrane shrinkage; may
produce harmful effect
15. OCULAR PIGMENT ABSORPTION
CHARACTERISTIC
• Melanin; Entire visible range-300 to
1300 nm(absorbs green, yellow, red
and infrared wavelengths).
• Absorbs mainly wavelength between
400-700 nm.
• Found mainly in the RPE (Retinal
pigment epithelium) and choroid
• Hemoglobin; range- 480 to 520nm
• Absorption varies according to oxygen
saturation.
• It absorbs yellow, green, and blue
wavelengths, but red light is absorbed
poorly.
16. OCULAR PIGMENT ABSORPTION
CHARACTERISTIC
CONTD
• Xanthophyll- in the macular;
Blue- 488nm(absorbs blue but
minimally absorbs yellow or red
wavelengths)
• Located in the inner and outer
plexiform retinal layers.
• It protects the photoreceptors from
short-wavelength light damage,
but can be damaged by blue light.
• When treating macular area, avoid blue lasers to
prevent inadvertent damage to the macula.
• Avoid blue lasers in Old people with lenticular
opacities: lens absorbs, more scattering
• Argon green, doubled frequencies Nd:Yag,
577dye are lasers of choice for macular
photocoagulation
17. SELECTION OF OPTICAL WAVELENGTH FOR
COAGULATION
• Wavelengths that are highly absorbed by
macular pigments (such as 488 nm) are
relatively contraindicated when treating in
or near the macula.
• Absorption of these wavelengths in macular
leads to heating and destruction of the nerve
fiber layer and vision loss.
• Double ND:YAG or green Argon suited
• Laser scattering and loss in patients
with cataract or in vitreous opacities
can be minimized using longer
wavelengths: yellow (577 nm) or red
(640–680 nm) •
• Large quantity of hemoglobin-
wavelengths between 520 and 580
nm are best suite
22. CHORIORETINAL BURN INTENSITY
CLASSIFICATION
• Light; barely visible retinal
blanching
• Mild; faint white retinal burn
• Moderate; opaque dirty white
retinal burn
• Heavy; dense white retinal
burn
23. PAN RETINAL PHOTOCOAGULATION (PRP) AND
SECTORAL PHC-INDICATIONS. 1,2
• Proliferative diabetic retinopathy (PDR): Very severe NPDR/ PDR( DRS, ETDRS)
• Retinal vascular obstructions (CRVO); CVOS
• Retinal vasculitis
• Proliferative Sickle cell retinopathy
• Ocular ischemic syndrome with proliferation
• Retinopathy of prematurity; Treatment of threshold and high-risk prethreshold retinopathy of
prematurity (ETROP)
24. DEFINITION OF TERMS
• POWER: No of photons emitted each second. Expressed
in watts .
• EXPOSURE TIME: The duration in seconds the
photons are emitted from the laser in each burn.
• SPOT SIZE: Diameter of the focussed laser beam
expressed in microns.
• Energy : No of photons emitted during an exposure of
any duration. Expressed in Joules. ( J = W * Second )
25. PROCEDURE-SAFETY/PRECAUTOARY MEASURE
• Proper laser protection goggles for all staff
assisting the procedure
• The laser safety filter on the delivery system
must be activated upon performing the
procedure.
• The procedure should be performed or
supervised by an experienced ophthalmologist
to avoid technical errors
26. TECHNIQUE-POSITIONING
• Slit lamp delivery system;
patient in a sitting position.
• Endolaser and transscleral
delivery systems, the patient is
supine.
• With LIO; patient may be
sitting or supine.
27. PAN RETINA PHOTOCOAGULATION- LASER
PARAMETERS
• Spot size 200-500 microns
• Duration 200 to 500 ms
• Power 140-250mW
(conventional): Up to 750mw
depending on media clarity and
delivery system.
• Aim is to create a moderate intensity burn.
• Each burn should be at least 1 burn width
apart.
• 900 burns are required for each half of the
retina.
• Total of 1800 to 2200 burns for complete
treatment PRP.
28. PROCEDURE/ TECHNIQUE (SLIT-LAMP
DELIVERY)
• General or local anaesthesia; GA,
topical anaesthesia or give
peribular (local block)
• Place lens by asking patient to
look up while lower lid is being
retracted(non GA cases)
29. PROCEDURE CONTD
• Once lens is placed, focus to
obtain clear view of retina.
• Some providers prefer to
divide treatment into two or
more sessions while others
elect to perform treatment in
a single session.
30. TECHNIQUE CONTD- LASER PRP
• Start temporally just outside the vascular
arcades and 3-disc diameters temporal to the
macula, and extending to or just beyond the
equator.
• Nasal side of the fundus; begin about 1-disc
diameter nasal to the optic disc and also
extend to or just beyond the equator(do not go
closer than 500 microns from the optic disc
margin).
31. PRCOCEDURE- PRP CONTD
• However, specific regimens vary by
practitioner.
• Inferior half of retina is treated in
first session and then superior half
after 15 days.
• If vitreous hemorrhage occurs, it
would be difficult to apply laser to
inferior half
32. PROPOSED THEORIES OF EFFECT OF PRP
• Injured RPE cells : thinning and
anoxia of the outer retina.
• More oxygen available to inner
retina and vitreous.
• Decreased stimulus for
neovascularisation.
• Also, PRP converts ischaemia to
anoxia, no VEGF
33. LASER INDIRECT OPHTHALMOSCOPE (LIO)
DELIVERY-INDICATIONS
• Media opacities like dense cataracts,
vitreous hemorrhage
• Peripheral retinal lesions like holes /tears
• Patients who cannot sit for long duration
• Parameters used are similar to that of slit
lamp delivery system but may require
higher power in dense media opacities.
35. SCATTER LASER PRP- ENDOLASER
• It is 360 degree PRP given with 2 burns width
occurring as distance between 2 separate
burns.
• Total of 800 to 1000 burns are required for
complete scatter PRP.
• INDICATIONS; patients undergoing pars
plana vitrectomy with indicating retina
lesions.
36. FOCAL/ GRID/ BARRAGE LASERS-INDICATIONS
• Clinically significant macular edema (CSME)
• Pin point leaks in central serous chorioretinopathy (CSCR)
• Branch retinal vein occlusions (BRVO)
• Focal ablation of extrafoveal choroidal neovascular membrane
• Treatment of ocular tumors
• Creation of chorioretinal adhesions surrounding retinal breaks and
detached areas
37. FOCAL/GRID PHOTOCOAGULATION-LASER
PARAMETERS
• Spot size 50-100 microns, up to 50 to 200
microns for grid lasers.
• Duration 0.1 seconds
• Power 50-100 mW . Power titrated to
barely whiten the microaneurysm.
• Blanches RPE / microaneurysms (light to
mild intensity)
38. FOCAL LASER
• Given for focal maculopathy i.e macular
edema caused by focal leakage.
• Laser is given directly to the microaneursyms
situated between 500 to 3000 microns from
fovea.
• This stops leakage by direct closure of
microaneursyms thereby inducing vascular
thrombosis.
39. FOCAL LASER CONTD
• If vision is less than 6/9 with
persistent edema and good peri
foveolar network on FFA then focal
laser up to 300 microns from fovea
may be considered.
• The spot size should be reduced to
50 microns and duration to 0.05
second in above senerio.
40. EFFECT OF FOCAL PHC- BEFORE AND AFTER
LASER
• Newer RPE replaced
• Causes existing RPE cells to
absorb more fluid.
• Stimulates endothelial proliferation
which promotes better integrity of
blood - retinal barrier
41. GRID LASER
• Grid pattern of laser is given for diffuse macular
edema i.e macular edema caused by diffuse leakage.
• The laser is applied to edematous areas avoiding
foveal avascular zone (FAZ), around 500 microns
from fovea.
• The spacing should be one burn width apart.
• It can be given in papillomacular bundle also but it
should remain 500 microns from the disc.
42. LASERS IN SPECIFIC CASES
• ROP; 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
RETINAL BREAK; Two-three rows of
confluent burns ꟷ Spot size: 200-500 μm ꟷ
Mild to moderate burn intensit
43. LASERS IN CHOROIDAL NEOVASCULARIZATION
(CNV)
• Choroidal neovascularization (CNV)
Conventional(direct) laser: 532 nm frequency
doubled YAG or argon green (514 nm)
• 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 until uniform whitening
is observed.
45. RECENT ADVANCES -PASCAL (PATTERN SCAN LASER)
PHOTOCOAGULATION
• PASCAL Photocoagulator is the
latest laser machine.
• It is a semi-automated pattern
generation technique that allows
the rapid delivery of 532
nanometer laser pulses in a
predetermined sequence.
46. ADVANTAGES OF PASCAL
• Very fast and more efficient than standard single
shot
• Improved comfort: Patients are likely to experience
less discomfort and therefore have more tolerance
for the procedure.
• Full 360 degrees PRP can be done in a single sitting
• Advanced precision: Macular Grid treatment
provides an improved margin of safety and
dosimetry control when compared with single shot
treatments.
47. PASCALADVANTAGES CONTD
• Unlike the irregular pattern
placement obtained in single shot
photocoagulation, PASCAL delivers
even pattern burns.
• Easier to use as physician training is
minimal and photocoagulation is the
same with conventional lasers.
48. RECENT ADVANCES -SELECTIVE RPE THERAPY
(SRT): MICROPULSE LASER
• Light is strongly absorbed by melanosomes in
the RPE
• Application of microsecond laser pulses allows
for confinement of the thermal and mechanical
effects of this absorption within the RPE layer,
thus sparing the photoreceptors and the inner
retina.
• Sub-thresh hold
• Subsequent RPE proliferation and
migration restores continuity of
the RPE layer
• Lack visible changes in retina •
CSR, DM
49. RECENT ADVANCES; NAVIGATED LASERS
• NAVILAS an example
• 532-nm pattern-type eye-tracking laser integrateslive
colour fundus imaging, red-free and infra-red imaging,
• FFA with photocoagulator system
• After image acquisition and making customized
treatment plans by the ophthalmologist
• Marking areas which will be coagulated, the treatment
plan is superimposed onto the live digital retina image
during treatment
• The ophthalmologist controls laser
application and the systems assist with
prepositioning the laser beam
50. COMPLICATIONS OF LASER PROCEDURES
• Discomfort
• Ocular Pain, headache
• Anterior segment; corneal or lenticular
opacification
• Transient visual loss
• Photocoagulation of the fovea
• Macular edema
• Hemorrhage: Vitreous
• Choroidal Effusion
• Color vision alterations
• Visual field defects and night vision
problems
• Iatrogenic retinal break
• Vitreoretinal traction
51. CONCLUSION
• Although, the advent of anti-VEGF has taken over as first line option in many
previous indications of retinal laser photocoagulation.
• Recent advancements and introduction of retinal sparing lasers with improved
visual outcome will no doubt advance the use of Lasers in retina disease
conditions.
• Therefore, understanding the basics of retinal laser photocoagulation is
paramount.
52. REFERENCES
• Shah PK, Prabhu VV, Morris RJ. Pan Retinal Photocoagulation (PRP), Focal Laser & Photodynamic
Therapy (PDT) Technique & Tips. eOphtha. [accessed mach 21, 2023]. Available from
https://www.eophtha.com/posts/pan-retinal-photocoagulation-prp-focal-laser-photodynamic-therapy-
pdt-technique-
tips#:~:text=Under%20topical%20anaesthesia%2C%20place%20lens,obtain%20clear%20view%20of%
20retina.
• David G Telander DG, Dahl AA. Retinal Photocoagulation. Medscape. Updated: Jul 26, 2016. [accessed
mach 21, 2023]. Available from https://emedicine.medscape.com/article/1844294-overview#a3
• Classification and treatment of Diabetic Retinopathy: diabetic maculopathy In: AMP Hamilton, MW
Ulbig, P Polkinghorne, editors.Management of Diabetic Retinopathy. 1st Indian edition reprint 2003
Jaypee Brothers medical publishers Pvt Ltd New Delhi; 2003;
53. REFERENCES CONTD
• Chhabiani J et al Restorative retina laser therapy; present state and future direction. Surveey of ophthalmology. Scirnce Direct
• Abouammoh MA et al. Lase surgey. Eye wiki available from www.eyewiki.aao.org/lasers_(surgery)#
• Rosenblatt RJ, Benson WJ. Diabetic Retinopathy. In: Yanoff M, ed.Opthalmology. 2nd ed. St. Louis, MO: Mosby; 2004;877-
887.
• Techniques for scatter and local photocoagulation treatment of diabetic retinopathy: Early Treatment Diabetic Retinopathy
Study Report no. 3. The Early Treatment Diabetic Retinopathy Study Research Group. Int Ophthalmol Clin. 1987
Winter;27(4):254-64.
• Aveline, B, Hasan, T, Redmond, RW (1994) Photophysical and photosensitizing properties of benzoporphyrin derivative
monoacid ring A (BPD-MA)Photochem Photobiol59,328-335
• Schmidt–Erfurth, U, Hasan, T, Gragoudas, E, Michaud, N, Flotte, TJ, Birngruber, R. (1994) Vascular targeting in
photodynamic occlusion of subretinal vesselsOphthalmology101,1953-1961
