![Diode laser (810 nm):-
•It is the most important semiconductor laser [GaAlAs (720-890nm)GaAs (810nm)]
•Direct photocoagulation of microaneurysmis difficult becauseit is poorly absorbed by hemoglobin.
•However, it is as effective as argon, freq-doubled Nd: YAG laser in reducingmacular edema.
•It offers increasedpatient comfort due to absence of bright flash of light.
•However, due to deeper penetration in to the choroids, it may bepainful if the intensityof retinal coagulation is
not properly titrated /reduced.
•It is a low cost, portable, small, high powered and versatile laser.](https://image.slidesharecdn.com/lasersinophthalmology-200608045527/85/Lasers-in-ophthalmology-15-320.jpg)
Lasers in ophthalmology
- 1. LASERS IN OPHTHALMOLOGY Dr. NIKITA JAISWAL
- 2. HISTORY: • In 1916, ALBERT EINSTEIN laid the foundation for invention of laser • Laser was coined by GURDEN GOULD. • The first working laser in ophthalmology was made by THEODORE MAIMAN,1960. • He utilized a pulsed ruby laser coupled with a monocular direct ophthalmoscopic delivery system.
- 3. GLOSSARY • INTRODUCTION • PROPERTIES • TYPES • LASER –OPHTHAL RELATION • APPLICATIONS • MODE OF DELIVERY • AREA OF INTEREST
- 4. L: LIGHT A: AMPLIFIED BY S: STIMULATED E: EMISSION R: RADIATION
- 5. INTRODUCTION PROPERTIES: • Coherence: wavelengths of the laser light are in phase in space and time. • Monochromatic light : beam of single wavelength. • Collimation: all rays are parallel to each other.
- 7. Genesis
- 11. Diode 810nm Krypton red 647nm Krypton yellow 568nm Frequency doubled 532nm NdYAG Argon green 514nm Argon blue 485nm
- 12. Green Argon laser (514.5 nm) •It is absorbed selectively at the retinal pigment epithelium (RPE), hemoglobin pigments, chorio-capillaries, layer of rods and cones and at the outer and inner nuclear layers. •It is readily absorbed by the melanin granules. •It coagulates from chorio capillaries to inner nuclear layer of the retina. •It is suitable for photocoagulation of retinal pigment epithelium (RPE), choroids and blood vessels.
- 13. Freq-doubled Nd: YAG laser (532 nm) •Itproduces a pea-green beam. •It is often termedas “green Nd: YAGlaser” or “KTP laser”. •It is more highlyabsorbed by hemoglobin (Hb) and the melaninpresent inretinal pigment epithelium (RPE) and trabecular meshworkthan the argon laser beam. It coagulates from choriocapillaries to outernuclearlayerof the retina. •Itis small and portable likediode laser. •It is a solid state and diode pumped CWlaser. •Itcauses photocoagulation with least energy trans- mission and shows considerable safety in maculartreatment. Hence, it is fast gaining major marketshare of posterior segment photocoagulator.
- 14. 1.Krypton red laser (647 nm) 1. Themelaningranules also readily absorb it. 2. It is not absorbed by the hemoglobin (Hb) and xanthophylls pigments present in the maculararea. Hence,it is particularly suitable for macularphoto- coagulation and coagulation of subretinal neovascular membrane. 3. It coagulates deeper into the retinal pigment epithelium . 4. (RPE) and choroids. It has insignificant photo- coagulation effect onthe vascular system of the retina. Itis less absorbed and more highlytransmitted throughretinal pigment epithelium (RPE) . So, it is able to produce more extensive and deep coagulation of choriocapillaries and choroids.
- 15. Diode laser (810 nm):- •It is the most important semiconductor laser [GaAlAs (720-890nm)GaAs (810nm)] •Direct photocoagulation of microaneurysmis difficult becauseit is poorly absorbed by hemoglobin. •However, it is as effective as argon, freq-doubled Nd: YAG laser in reducingmacular edema. •It offers increasedpatient comfort due to absence of bright flash of light. •However, due to deeper penetration in to the choroids, it may bepainful if the intensityof retinal coagulation is not properly titrated /reduced. •It is a low cost, portable, small, high powered and versatile laser.
- 16. Light tissue interactions: Photocoagulation Photodisruption Photoablation photoactivation
- 17. Types: • Solid state:ruby,Nd:yag • Gas lasers: argon,krypton,neon,helium • Excimer: argon fluoride
- 18. Photocoagulation: • Laser light is absorbed by the RPE & then it produces heat which denatures the proteins. • Light energy applied to tissue changes to thermal energy –tissue temperature rises by 65’c which causes coagulative necrosis. • This heat coagulate the pigmented & adjacent tissues. • The outer layers are more effected than the inner layers.
- 19. Types of lasers in photocoagulation • Green argon laser (514.5 nm) • Freq doubled Nd:YAG laser (532 nm) • Krypton red laser (647nm) • Diode laser(810nm)
- 20. Photodisruption: • The energy produced is released in a very short time. • The laser beam is focused, concentrating the power into small area • It produces a spark & an acoustic wave—which disrupts the tissue. • ex:Nd:YAG laser.
- 21. Photoactivation • It is a conversion of chemical from one form to another by light. • ex-the use of verteporfin –a drug that is chemically inert but is activated by light ,after which it destroys neovascular tissue.
- 22. Photoablation : Temperaturerise does not take place in the shorter wavelengths of the ultraviolet spectrum. At the site of impact, the tissue simply disappears without any charringand temperature rise. Surface of the target tissue can be precisely removed, layer-by-layer,in photoablation. Photoablation with 193 nmargonfluoride (ArF) excimer
- 24. Laser parameters Laser Parameters •Power = Numberof”photons”emitted each second and is expressed in watts (W). •Exposure time = Theduration in second (sec.) the “photons” are emitted ineach burn from thelaser. •Spot size = Thediameter of the focused laser beam and is expressed in micron(μm).
- 26. OUR SCOPE : laser PCIOL RETINAL DEGENERATIONS Glaucoma LPI ALT SLT Retina DR/FOCAL /GRID
- 30. Pattern of capsulotomy opening • Cruciate opening: It is the usual choice. Thefirst shot is made superiorly in the location of some fine tension lines at 12o’ clock and progressing towards 6 o’ clock. •Christmas tree pattern opening: Thistype of opening is preferred whenthereis increased tendency to intraocularlens pitting (IOL pitting) or damage due to presence of minimumgap orno gap between posterior surface of intraocularlens andopacified posterior capsule. •Revised Hexagonal Capsulotomy technique
- 32. Follow-up Schedule Inour countrythe following protocol of follow up is feasible or advisable. 1st follow up visit –Next day or day after tomorrow. 2nd follow up visit – One/two weeks. 3rd follow up visit – Four/six weeks. COMPLICATIONS : TRANSIENT ELEVATION OF IOP IOL PITTING ACUTE GLAUCOMA RRD LESS COMMON IRITIS HYPHAEMA MACULAR HOLE ENDOPHTHALMITIS
- 33. LASERS IN GLAUCOMA • ALT • SLT • LASER PERIPHERAL IRIDOTOMY
- 34. Application of continuous wave Argon Laser either bichromatic blue-green (454.4–528.7 nm ) or mono- chromatic green ( 514.5 nm ) non penetrating coagulative burns to the trabecular meshwork ( TM ) results in improved aqueous outflow. Laser thermalenergyis absorbed by pigmented trabecularmeshwork. Possibly this causes increasedspace inintertrabecular space due to shrinkageof collagen fibrils of trabecular lamellae andleads to increasedaqueous outflow throughthe trabecular mesh-work. Shrinkageof collagen fibrils also tightens the trabecularmeshwork ringand opens up drainage pores. Macrophages migrateinto the treated area and engulf extracellular matrix(ECM)..
- 35. ALT Technique Proper 1.Parameters: Energy:400-1200mW, exposure-0.1 second and spot size-50μ(micron). 2.No.of laser burns: Single session schedule-100burns over entire360 degree. Double session schedule-50burnsover 180degree intwo sessions at 4 weeks interval.
- 36. End point of optimal energy effect: Blanching or tissue whitening with minimal or no bubble formation Large bubble formation indicates energy level is too high If the tissue reaction is inadequate, increase the energy/power by 200 mW until optimal end point is achieved by least power. Site of focus: At the junction of the anterior nonpigmented and posterior pigmented trabecular meshwork If properly focused the laser focus will be perfectly round with a clear outline. A = Schwalbe’s Line, B = Nonpigmented trabecular meshwork, C = Pigmented trabecular meshwork, D = Scleral Spur and E= Ciliary Band
- 37. 1 and 2= Blanching or tissue whitening with no bubble formation Ideal, 3 =The aiming beam is ill focused the laser focus is oval with blurred edge unacceptable, 4 =Minimal or small bubble formation Acceptable, 5 =Slight discoloration Acceptable and 6 = Large bubble formation Indicates too high power setting Unacceptable,
- 38. SLT • Selectiave Laser Trabeculoplasty” (or Selective Laser Trabeculotherapy) is performed with a frequency doubled Nd:YAG laser ( 532 nm ). It has replaced argon laser trabeculoplasty (ALT) due to lack of damage to the trabecular meshwork. • It selectively targets the melanin granules within the cells of the pigmented trabecular meshwork (TM). Disruption of the melanin granules cause cell death termed as “selective photothermolysis ”. • There is no structural or photocoagulative damage to the trabecular meshwork (TM). • Eliminates scarring (seen in ALT) which is responsible for reduced aqueous outflow.
- 40. . Parameters: Energy—0.6-1mJper pulse (to avoid bubble formation) Pulse duration—3nanosecond (ns) and Spot size—400μm. 2.No. of laser burns: 50single short pulses 3ns ) spread over 180 degree of the trabecularmeshwork (inferior/ nasal quadrant). 3.End point of optimal energy effect: Thereis no end point like blanching or tissue whitening or bubble formation as seen in ALT 4.Site of focus: Theshots cover entire heightof trabecular meshwork. 1 = Schwalbe’s Line, 2 = Nonpigmented trabecular meshwork, 3 = Pigmented trabecular meshwork, 4 =Scleral Spur and 5= Ciliary Band. Left: Argon Laser Trabeculoplasty-50 μm laser spots at the junction of the pigmented and nonpigmented trabecular meshwork, 150 μm apart; Right: Selective Laser Trabeculoplasty-400 μm confluent laser spots covering entire height of the trabecular meshwork
- 42. LPI:
- 43. Iridotomy Technique Proper(ARGON) “Hump” technique: Initially a “hump” is created on the iris with contraction burn of 500 μm spot size, 200-400 mW energy and 0.5-second exposure. The hump is penetrated full thickness with 50 μm, 700-1200 mW and 0.1/0.2 second burns. Drumhead” technique: Initially stretch burns areplaced circularlyaround the site of iridotomy with 200 μm, 200 mWand 0.2sec. Parametersto create taughtness of the centralarea like “drumhead”. Thecentral area is penetrated with 50 micron, 700-1200 mW and 0.1/0.2 second burns.
- 44. ND YAG LPI: • Insertion of contact lens: Commonly Abraham contact • Lens is used. It has a +66 diopter peripheral button over a routine contact lens
- 45. Iridotomy Technique Proper •Usually, 3-8 mJ per shot from Nd: YAG laser andone to three shots are sufficient to complete the procedure. •A full thickness opening in iris in one shot is the optimal target. Often up to four shots areneeded toachieveperforation ofiris. •Axis of the focusing beam should coincide with the axis of the contact lens. •Conditions/situations whereuse ofcontact lens is avoided higherenergyis required and more central iridotomy is to bemade. •If the anterior chamberdepth is nil, the pulse energyshould not exceed10-12 mJ.
- 46. •Optimal siteof iridotomy • Between 10 o’ clock and 2 o’ clock. • Avoid 12 o’ clock site-here gas bubble may obstruct the siteof the opening. • Will becoveredby the uppereyelid. • About three-fourth of the distance between pupillary margin and iris periphery. • Avoid arcus senilis —The opacity interferes with clear focus and transmits less laser energy. • Avoid visible iris vessels.
- 47. 1.Follow-up Schedule Thefollowing protocol is suggested: 1st follow up—next day or day after tomorrow. 1. 2nd follow up—one week postlaser. 2.3rd follow up—three weeks postlaser. 3.4th follow up—six weeks postlaser.
- 48. Retinal lasers
- 50. Laser delivery systems: Indirect ophthalmoscope Slit lamp biomicroscope Endophotocoagulation
- 52. Know what we have……
- 55. Burn intensity light Barely visible retinal blanching mild Faint white retinal burn Moderate Opaque,dirty white retinal burn heavy Dense-white retinal burn
- 57. OCULAR TISSUES LIGHT ABSORBED LIGHT PASSED MELANIN GREEN,YELLOW,RED & INFRAREDS XANTHOPHYLL BLUE YELLOW & RED HAEMOGLOBIN BLUE, GREEN & YELLOW RED
- 58. Practical aspects of laser photocoagulation • Anaesthesia:topical,peribulbar/retrobulbar • Lenses:2 types of contact lenses 1-negative-power planoconcave lenses. 2-high-plus-power lenses. Negative power -Upright image with superior resolution. -favoured for macular treatment -provide the same retinal spot size. High plus power -Inverted image -Offer a wide field of view -provide a spot size that is magnified over the laser setting size.
- 59. Choice of laser wavelength: • Focused on the degree to which photocoagulation must be targeted to a particualr tissue sparing the normal tissue. • Area directly related to intensity & duration of irradiation. Lasers characteristic Preferred Green laser Absorbed well by melanin & Hb Retinal vascular abnormalities/CNV Red laser Good penetration & cause deeper burns Moderate vitreous hemorhages Yellow laser Minimal scatter & little potential for photochemical changes. Retinal vascular & choroidal neovascularizarion
- 60. PRP • Gas laser • Mechanism: PHOTOCOAGULATION • 514.5 nm wavelength(visible) INDICATIONS • Diabetic retinopathy • Macular edema • CRVO/BRVO • Eales disease • sickle cell retinopathy,coats disease
- 62. PRP/Scatter Photocoagulation Technique Proper 1.PRP is usually divided over 3 sessions with 1-2week(s) interval between thesessions. 2.TheDiabetic Retinopathy Study (DRS) protocol recommended 800-1600burnsin PRP. However, 1800-2200burns are often reported. 3.Location of PRP burns—Itextends from 500 μm nasal to the optic disc margin, 2DD(3000 μm) temporal to, above and below the macular center, just within the vascular arcade and extending peripherally to or beyond the equator.
- 63. SITTING: • 3 SITTINGS • INTERVAL 1-3 WEEKS • 1800 applications of 500 µm retinal spot size,0.1 to 0.2 sec duration (180mw to start with) SESSION SPOT SIZE POWER EXPOSURE 1ST 100-200µm 100-400mw 0.05-0.2 sec 2ND 300-500µm 400-800 mw 0.1-0.2 sec 3RD 300-500 µm 400-800 mw 0.1-0.2 sec
- 66. Modertae to heavy laser burns Laser in PRP
- 68. FOCAL PHOTOCOAGULATION: SPOT SIZE EXPOSURE POWER 50-100µm 0.1 SEC 100-400mw : Areas 5oo µm away from disc margin & centre of macula but within within 3000µm
- 69. complications • Paracentral scotoma • Transient increase of edema • Photocoagulation scar expansion • Subretinal fibrosis at laser site • Inadvertent foveolar burns
- 70. Grid photocoagulation Indication: Previously untreated areas of diffuse leakage in the retina -Areas 5oo micron away from disc margin & centre of macula are excluded Grid laser is usually placed on papillo-macular bundle Spot size exposure Power 50-200µm 0.1 sec 50-100mw Lasers used:- argon green & yellow
- 72. Retinal degeneration: • Parameters • Spot size—500-800 μm • Exposure—0.1-0.2 sec. • Power—*400-600 mW • Pattern—Usually solitary, linear, single row and interrupted (interval = 1⁄2 of spot size)
- 73. 1.Thephotocoagulation burnsshould beplaced at least 1 DD (Disc diameter) i.e. 1500 μm away from theborder of 2.the peripheral retinal degeneration. 3.Initially, most anteriormargins are photocoagulated. 4.If thedegeneration is extensive or considerable vitreous 5.traction is present, initial single row of coagulation may be reinforcedbydouble row of linear, interrupted coagulation
- 74. Pattern scan laser: • This is done in single spots with pulse durations of 10 to 20 ms rather than conventional 100-200 ms • Multispot laser delivers multiple uniform laser burns simultaneously by a single foot pedal depression in a variety of pattern. • Patterns are:- Pattern Retina Macula Square arrays 5*5 Arcs Concentric rows varying from 1 to 3 Exclusion zone upto 2mm circular For small hole
- 75. Disadvantages • The spot size is restricted (100,200& 400micron) • Inability to design the pattern • It produces some more noise. • Difficulty in penetration through media opacities.
- 76. Micropulse laser: • This was invented by pankratov in 1990 in this the laser energy in short-pulse or in micropulse. • Parameters:- retinal spot size,laser energy & duration constant, size of retinal lesion is governed by DUTY CYCLE. • Longer the OFF time between pulses lesse will be the duty cycle= less damage to tissue & less heat produced. Cumulative refraction time between pulses.
- 78. Take home seminar message: 1. ultraviolet photokeratoconjunctivitis (also known as ‘welder’s flash’ or simply ‘photo- keratitis’. 2.one aspect of ‘snow-blindness’ from wavelengths of ~180- 400 nm) 3.ultraviolet cataract (~295-325 nm – and perhaps to 400 nm). This is expected only from chronic exposure under normal. 4. Choice of lasers should be based on the type of tissue we are interested in. 5.Photocoagulation temp. of treated tissue is raised from 37’c to 50’c 6.Argon green and diode lasers are delivered through Laser Endoscope during vitrectomy.