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Lasers in ophthalmology
1. ROLE OF LASERS IN OPHTHALMOLOGY
Presenter : Dr. Ajay Gulati
2. HISTORY
๏ Dates to 400 BC, when Plato described the dangers of direct sun
gazing during an eclipse
๏ Czerny and Deutschmann, in 1867 and 1882, respectively,
focused sunlight through the dilated pupils of rabbits
๏ Meyer-Schwickerath undertook the study of retinal
photocoagulation in humans in 1946 using the xenon arc lamp
๏ The first functioning laser was demonstrated by Maiman in
1960. The active laser material was a ruby which emitteda
radiation of 649 nm (red light) pulsed with a xenon flash lamp
๏ First clinical ophthalmic use of a laser in humans was reported
by Campbell et al. in 1963 and Zweng et al. in 1964
๏ Argon laser was developed in 1964, LโEsperance conducted the
first human photocoagulation with it
๏ He also introduced the frequency-doubled neodymium:yttrium-
aluminum-garnet (Nd:YAG) and krypton lasers in 1971 and 1972,
respectively
๏ Q-switched , mode-locked , tunable dye laser , semiconductor
infrared diode laser were other sequential discoveries
3. INTRODUCTION
๏ LASER stands for Light Amplification by Stimulated
Emission of Radiation
๏ The basic laser cavity consists of an active medium in a
resonant cavity with two mirrors placed at opposite ends.
One of the mirrors allows partial transmission of laser
light out of the laser cavity, toward the target tissue. A
pump source introduces energy into the active medium
and excites a number of atoms. In this manner,
amplified, coherent, and collimated light energy is
released as laser energy through the mirror that partially
transmits. The various lasers differ mainly in the
characteristics of the active medium and the way this
active medium is pumped
4.
5.
6. Properties of laser light that make it
useful to ophthalmologists
๏ Monochromaticity
๏ Spatial coherence
๏ Temporal coherence
๏ Collimation
๏ Ability to be concentrated in a short time
interval
๏ Ability to produce nonlinear tissue effects
10. DELIVERY SYSTEMS
๏ Slit-lamp biomicroscope : most common, delivery is
transcorneal, with or without the aid of contact
lenses
๏ Indirect ophthalmoscope : condensing lens ,
transcorneal
๏ Endolaser probes : fiber-optic probes used within
the eye
๏ Exolaser probes : fiber-optic probes used trans-
sclerally
11. PARAMETERS AND TECHNIQUES
๏ Wavelength: choice of optimal wavelength
depends on the absorption spectrum of the target
tissue
๏ PRINCIPAL WAVELENGTHS OF COMMONLY USED LASERS
๏ 193 nm - Excimer (Cornea)
๏ 488 - 514 nm - Argon (Retina)
๏ 532nm - Frequency doubled Nd:YAG
๏ 694.3 nm - Ruby
๏ 780 - 840 nm - Diode
๏ 1064 nm - Nd Yag (Capsule)
๏ 10,600 nm - Carbon dioxide (Skin)
15. PHOTORADIATION (PDT):
๏ Also called Photodynamic Therapy
๏ Photochemical reaction following visible/infrared light
particularlyafteradministration ofexogenous chromophore.
๏ Commonly used photosensitizers:
๏ง Hematoporphyrin
๏ง Benzaporphyrin Derivatives
16. ๏ Photon + Photosensitizer in ground state (S)
๏ฏ
high energy triplet stage
๏ฏ
Energy Transfer
๏ฏ ๏ฏ
Molecular Oxygen Free Radical
S + O2 (singlet oxygen), Cytotoxic Intermediate
๏ฏ ๏ฏ
Cell Damage, Vascular Damage , Immunologic
Damage
17. Photoablation:
๏ Breaks the chemical bonds that hold tissue
together essentially vaporizing the tissue, e.g.
Photorefractive Keratectomy, Argon Fluoride (ArF)
Excimer Laser.
19. ๏ Photovaporization
๏ Vaporization of tissue to CO2 and water occurs when
its temperature rise 60โ100 0C or greater.
๏ Commonly used CO2
๏ฏ
Absorbed by water of cells
๏ฏ
Visible vapor (vaporization)
๏ฏ ๏ฏ
Heat Cell disintegration
๏ฏ ๏ฏ
Cauterization Incision
21. MODES OF OPERATION
๏ Continuous Wave (CW) Laser: It deliver the energy
in a continuous stream of photons.
๏ Pulsed Lasers: Produce energy pulses of a few tens
of micro to few mili second.
๏ Q Switched Lasers: Deliver energy pulses of
extremely short duration (nano second).
๏ Mode-locked Lasers: Emits a train of short
duration pulses (picoseconds) to femtoseconds
๏ Pulsed pumping
22. Safety
Lasers are usually labeled with a safety class number, which identifies
how dangerous the laser is
๏ Class I/1 is inherently safe, usually because the light is contained
in an enclosure, for example in CD players.
๏ Class II/2 is safe during normal use; the blink reflex of the eye will
prevent damage. Usually up to 1 mW power, for example laser
pointers.
๏ Class IIIa/3R lasers are usually up to 5 mW and involve a small
risk of eye damage within the time of the blink reflex. Staring into
such a beam for several seconds is likely to cause damage to a spot
on the retina.
๏ Class IIIb/3B can cause immediate eye damage upon exposure.
๏ Class IV/4 lasers can burn skin, and in some cases, even scattered
light can cause eye and/or skin damage. Many industrial and
scientific lasers are in this class.
26. Scanning Laser Ophthalmoscopy
๏ In the scanning laser ophthalmoscope (SLO), a narrow laser
beam illuminates the retina one spot at a time, and the
amount of reflected light at each point is measured. The
amount of light reflected back to the observer depends on the
physical properties of the tissue, which, in turn, define its
reflective, refractive, and absorptive properties. Media
opacities, such as retinal hemorrhage, vitreous hemorrhage,
and cataract, also affect the amount of light transmitted back
to the observer. Because the SLO uses laser light, which has
coherent properties, the retinal images produced have a much
higher image resolution than conventional fundus
photography.
๏ study retinal and choroidal blood flow
๏ microperimetry, an extremely accurate mapping of the
maculaโs visual field.
27.
28. Tests Performed on the Scanning Laser
Ophthalmoscope
๏ Scanning Laser Acuity Potential (SLAP) Test: The letter E
corresponding to different levels of visual acuity (ranging from
20/1000 to 20/60) is projected directly on the patientโs retina. The
examiner directs the test letters to foveal and/or extrafoveal locations
within the macula, and determines a subjectโs potential visual acuity.
This is especially helpful in individuals who have lost central fixation
but still possess significant eccentric vision.
29.
30. ๏ Microperimetry / Scotometry : The SLO could visualize a
particular area of the retina and test its sensitivity to visual stimuli,
thereby generating a map of the seeing and non-seeing areas.
31. ๏ Hi-Speed FA / ICG
๏ Fluorescein and Indocyanine Green Angiography (FA/ICG) performed
using the SLO is recorded at 30 images per second, producing a real-
time video sequence of the ocular blood flow
32. Optical Coherence Tomography
๏ diode laser light in the near-infrared spectrum (810 nm)
๏ partially reflective mirror used to split a single laser beam into two, the
measuring beam and the reference beam
๏ measuring beam is directed to the retina , laser beam passes through the neurosensory
retina to the retinal pigment epithelium (RPE) and the choriocapillaris. At each optical
interface, some of the laser light is reflected back to the OCTโs photodetector
๏ reference beam is reflected off a reference mirror at a known distance from the beam
splitter, back to the photodetector. The position of the reference mirror can be adjusted to
make the path traversed by the reference beam equal to the distance traversed by the
measuring beam to the retinal surface. When this occurs, the wave patterns of the measuring
and reference beams are in precise synchronization, resulting in constructive interference.
This appears as a bright area on the resulting cross-sectional image. However, some of the
light from the measuring beam will pass through the retinal surface and will be reflected off
deeper layers in the retina. This light will have traversed a longer distance than the reference
beam, and when the two beams are brought back together to be measured by the
photodetector, some degree of destructive interference will occur, depending on how much
further the measuring beam has traveled. The amount of destructive interference at each
point measured by the OCT is translated into a measurement of retinal depth and graphically
displayed as the retinal cross-section.
๏ OCT images are displayed in false color to enhance differentiation of retinal structures. Bright
colors (red to white) correspond to tissues with high reflectivity, whereas darker colors (blue to
black) correspond to areas of minimal or no reflectivity. The OCT can differentiate structures
with a spatial resolution of only 10 ฮผm
33.
34. Wavefront Analysis and Photorefractive
Keratectomy
๏ Lasers are used in the measurement of complex
optical aberrations of the eye using wavefront
analysis
๏ Hartmann-Shack aberrometer
43. LASIK jjj
๏ผ 2 to 9 D
๏ผ lamellar dissection with the microkeratome
๏ผ refractive ablation with the excimer laser
๏ผ IntraLASIK/Femto-LASIK or
All-Laser LASIK ( corneal flap is made with
Femtosecond laser microkeratome)
45. Femto lasers in cataract surgery
๏ LenSx Lasers (ALCON)
๏ new level of precision and reproducibility
๏ The Laser creates
a) Corneal incisions with precise dimensions and geometry.
b) anterior capsulotomies with accurate centration and
intended diameter, with no radial tears.
c) lens fragmentation (customized fragmentation patterns)
46. Lasers in Glaucoma
๏ Laser treatment for internal flow block
๏ Laser treatment for outflow obstruction
๏ Miscellaneous laser procedures
49. ๏ ND:YAG Laser iridotomy : Q-switched Nd:YAG lasers
(1064 nm)
๏ 2โ3 shots/burst using approximately 1โ3 mJ/burst
๏ opening of at least 0.1 mm.
50. ๏ Argon or Solid-State Laser iridotomy:
Photocoagulative (lower energy & longer exposure)
Iris color (pigment density) is the most imp factor
Iris color can be divided into three categories:
a) light brown : 600โ1000 mW with a spot size of 50 ยตm and a
shutter speed of 0.02โ0.05 second
b) dark brown: 400โ1000 mW , spot size of 50 ยตm and a shutter
speed of 0.01 second
c) blue iris: 200- ยตm spot, 200โ400 mW, 0.1
Second to anneal the pigment epithelium to the stroma , Then the
spot size reduced to 50 ยตm and power increased
to 600โ1000 mW at 0.02โ0.1 second to perforate
64. Cyclophotocoagulation
๏ Trans-scleral Cyclophotocoagulation
A) Noncontact Nd:YAG laser cyclophotocoagulation
B) Contact Nd:YAG laser cyclophotocoagulation
C) Semiconductor diode laser trans-scleral
cyclophotocoagulation
๏ Endoscopic cyclophotocoagulation (ECP)
65.
66.
67.
68. Laser suture lysis (LSL)
When lasering sutures, the flange of
the Hoskins laser suture lens holds up
the lid. The suture is located under the
laser slit lamp
lens is pressed steadily against the
conjunctiva, displacing edema until a
clear image of the suture is seen . The
suture usually is treated near the knot.
The long end of the suture will then
retract into the sclera
69.
70. ๏ Laser synechialysis : lyse iris adhesions
๏ Goniophotocoagulation: anterior segment
neovascularization , rubeosis , fragile vessels in a
surgical wound
๏ Photomydriasis (pupilloplasty) : enlarge the
pupillary area by contracting the collagen fibers of
the iris
74. Laser in vitreous
๏ Vitreolysis in cystoid macular edema
๏ Viterous membranes & traction bands
75. Laser Photocoagulation In Vascular Diseases
๏ Panretinal Laser Coagulation
a) Full Scatter Panretinal Laser Coagulation
b) Mild Scatter Panretinal Laser Coagulation
๏ Focal Laser Application
๏ Subthreshold Laser Coagulation for Retinal
Disease
76. Full Scatter Panretinal Laser
Coagulation
๏ Diabetes : four accepted indications for a dense (full
scatter) panretinal laser coagulation are
a) Presence of vitreous or preretinal hemorrhage
b) Location of new vessels on or near the optic disk (NVD)
c) Presence of new vessels โelsewhereโ (NVE)
d) Severity of new vessels (proliferation area greater
than one-fourth of the optic disk size)
exposure times 100โ200 ms ,a spot size of 500 ฮผm. The laser
application should lead to a mild white retinal lesion. The
distance between the laser spots 0.5โ1 laser spot. range of laser
spots varies between 1,000 and 2,000 . It is recommended to
apply laser lesions in Two to four sessions, 2 weeks apart ,
Regression expected after 4โ6 weeks
77. ๏ Central Retinal Vein Occlusion: main
complications of a central vein occlusion apart from
macular edema are neo-vascularizations of the retina
and of the iris
๏ no effect of prophylactic pan-retinal laser
coagulation to prevent neovascularizati-ons of the
iris. But if neovascularizations of the retina or of the
iris exist,the treated eyes clearly benefit from full
scatter panretinal laser coagulation
78. ๏ Branch Retinal Vein Occlusion: characterized by
macular edema and vitreous hemorrhage from retinal
neovascularizations
๏ Retinal laser coagulation done not earlier than 3โ6
months.
๏ done only if retinal hemorrhage has significantly cleared.
๏ For the treatment of macular edema, exposure times of
100 ms and a spot size of 100 ฮผm are recommended. The
distance of 2โ3 spot diameters. The area of the edema
should be treated in a dense grid. After occurrence of
neovascularizations a sector retinal laser coagulation is
indicated.
79. Mild Scatter Panretinal Laser
Coagulation
๏ For Non-proliferative diabetic retinopathy
๏ risk factors for treating non PDR
๏ The 4:2:1 rule
a) If either intraretinal bleeding occurs in 4 quadrants
b) Or if venous beading occurs in at least 2 quadrants
c) Or if intraretinal microvascular abnormalities
(IRMA) occur in at least one quadrant
600 laser spots of 500 ฮผm ,exposure times 100โ200
ms spots more spaced than full scatter.
80.
81. Focal Laser Application
๏ Clinically significant macular edema (CSME)
๏ It is present and should be treated by focal laser
coagulation if:
a) There is a clinical retinal thickening within 500 ฮผm
distance from the center of the macula
b) There is hard exudation within 500ฮผm distance from the
center of the macula with retinal thickening in the
bordering retina
c) There is a retinal thickened area by the size of at
least one papilla diameter within the distance of one
papilla diameter from the center of the macula
82. ๏ Placement of the laser coagulation spots has to be
decided by fluorescein angiography
๏ exposure times 100ms and a spot size of 100 ฮผm with
beginning power of 70โ80 mW.
๏ leads to a mild gray retinal lesion.
83. Subthreshold Laser Coagulation for
Retinal Disease
๏ Selective treatment of the RPE
๏ Diabetic macular edema
๏ Central serous retinopathy (CSR)
๏ Drusen in age-related macular degeneration (AMD)
89. Indications
๏ CNVs due to age-related macular degeneration,
pathologic myopia, angioid streaks and presumed
ocular histoplasmosis syndrome
๏ Retinal capillary hemangioma
๏ Vasoproliferative tumor
๏ Parafoveal teleangiectasis
90. ๏ For age-related macular degeneration and
pathologic myopia : i.v Verteporfin at 6mg/m2 BSA
over 10 mins. Five minutes after the cessation of
infusion, light exposure (laser emitting light of 692
nm) with an irradiance of 600 mW/m2 is started,
delivering 50 J/cm2 within 83 s .
๏ Angiod Streaks: light dose of 100 J/cm2 over an
interval of 166 s
91.
92.
93.
94. Other Uses Of Lasers in Post. Segment
๏ Drainage of subretinal fluid / haem