LASERS IN OPHTHALMOLOGY PART -1DR. BHARTI AHUJA

INTRODUCTIONA LASER (from an acronym,LIGHTAMPLIFICATION BY STIMULATED EMISSION OF RADIATION) is an optical source that emits photons in a coherent beam. The backformed verb to lase means to produce laser light or to apply laser light to.

HISTORYIn

1916, ALBERT EINSTEIN laid the foundation for invention of laser and its predecessor ,the MASER. The first working laser in ophthalmology was made by THEODORE.H MAIMAN,1960. It utilized a pulsed ruby laser coupled with a monocular direct ophthalmoscopic delivery system.

Principle of laser

HOW LASERS WORK??

PROPERTIES OF LASERSMONOCHROMATIC DIRECTIONAL COHERENCE-spatial

and temporal COLLIMATION/IN PHASE Ability to be concentrated in short time interval.

La se r ti e i te ra cti n s ssu n o

p h o to th e rm a l

p h o to ch e m i l ca

M e ch a n i l / ca p h o to i n i ti n o za o

P h o to co a g u l ti n / a o P h o to va p o ri ti n za o p h o to ca rb o n i ti n za o P h o to ra d i ti n / a o p h o to a b l ti n a o

p h o to d i p ti n sru o

PHOTOTHERMAL EFFECTS

Photocoagulation-absorption of light by targettissue results in a temperature rise which causes denaturation of proteins.

Visible and infrared wavelengths.

Argon green(514nm) Argon blue-green(488nm) Krypton red(647 nm) Ruby red(694nm) Diode(810nm) Frequency doubled Nd:YAG(532nm)

Key pigments in ocular tissuesMelanin(RPE

,choroid)green,yellow,red and infrared wavelengths. Xanthophyll(macula)-blue(minimal absorption of yellow ,red wavelengths) Hemoglobin(blood vessels)blue,greenand yellow(minimal absorption of red wavelengths)

PHOTOVAPORIZATION AND PHOTOCARBONIZATION

H i h e r e n e rg y l se r l g h t a b so rb e d b y ta rg e t ti e re su l n g g a i ssu ti V a p o ri ti n o f b o th i tra a n d extra ce l u l r w a te r. za o n l a

W h e n th e l ca l sto re o f w a te r i va p o ri d , th e n ca rb o n i ti o s ze za o O ccu rs.

C O 2 LA S E R ( I w a ve l n g th ) R e

PHOTOCHEMICAL EFEECTSphotoradiation./ PHOTODYNAMIC

photoablationHigh energy laser wavelength in far ultraviolet region(less than 350 nm )of spectrum are used to break long chain tissue polymers into smaller volatile fragments. Exposure time is shorter(nanoseconds) Excimer lasers

Intravenous administration of hematoporphyrin derivative, taken up by target tissue causes sensitization of target tissue.exposure of this tissue to red laser light induces the formation of cytotoxic free radicals. Exposure time is longer (minutes) Tunable dye lasers

PHOTOIONIZATION/MECHANIC AL EFFECTS

Photodisruption-high energy laser lightdeposited over a short interval to target tissue stripping electrons from molecules of that tissue.thiscloud of electrons and ionized molecules constitute a plasma. Rapid expansion of it causes an acoustic wave ,disrupting the tissue.

Infra red wavelengths,1064 nm(Nd:YAG)

SOLID STATE LASING Crystals material containin g rare earth

/ Ne,CO2 xecl dye lasers Ruby laser SEMICONDUCTOR /DIODE LASERS-Small and less power. laser IR and deep red wavelengths.

EXCIME DYE R Noble Reactive Complex gases(kr/ gases(Cl, organic Ar) Fl)+inert dyes(rhod Ionized gases(Ar, -amine form kr/Xe) 6G, in liquid/sus -pension WAVE- Infra Visible Ultra Tunable LENGTH red(1.064 red/far violet over a micron) IR(10.6 broad micromet range of er) waveleng EXAMP ND:YAG He,He- Arf(193) ths Tunable LE

GAS

Laser outputContinuous/constant amplitude/cw

Single pulsed Output varies with respect to time(alternating off and on periods) Q and Modelocking/gain switching Modest amount of energy. Each pulse has relatively high power. Energy is concentrated into very brief periods(micro to milliseconds) Nd:YAG excimer

Output is relatively constant with respect to time. Delivers overall more total energy. Less power. Delivers Energy over a relatively long period(fraction of a sec to a sec) Argon,krypton,dye ,diode laser

Laser parametersExposure Power Spot

time(0.1-0.2 sec)

size(100micron-macular area, 500micron-periphery) Laser contact lenses

Laser lenses in photocoagulation

Planoconcave Upright image High resolution of small retinal area. Magnify the laser spot size(1.08) Prototype-goldman 3 mirror lens,angulated at degrees59-ora serrata 67-equator 73 posterior pole

High plus power Inverted image Wide field of view(mild loss of fine resolution) Magnify the spot size(depending on the lenses) Panfundoscope-1.41 Mainster wide angle-1.47 Quadr Aspheric lens-1.92

Therapeutic indications of lasers in ophthalmology Lid lesions Conjunctival tumours Dacryocystitis Refractive errors Cataract Glaucoma Diabetic retinopathy Venous occlusions-CRVO/BRVO ARMD Tumours(melanomas,retinoblastomas) Miscellaneous(orbitotomies.suturolysis)

Diagnostic applicationsScanning

laser ophthalmoscopy/SLO Laser light with its coherent properties,produces the retinal images,that are having higher image resolution than fundus photography. High resolution,real time motion images of the macula without patient discomfort.

Optical coherence tomographyIt

uses diode laser light in the near infra red spectrum(810nm) to produce high resolution crosssectional images of the retina using coherence interferometry.

Wavefront analysisIt

is the study of the shape of the group of photons that leave an object at any point in time and how they are affected by optical media. Lasers are used in the measurement of complex optical aberrations of the eye using wavefront analysis.

Preoperative laser work upHistory

and visual acuity Evaluation of anterior segment IOP recording Visual fields Macular function tests Retinal and vitreous examination Flourescein/ICG angiography OCT

Nd:YAG LASERqSolid state(PHOTODISRUPTION) Wavelength (1064nm,IR region) Invisible pulses,red aiming beam.

Q switch power 10(6) to 10(9)watts Pulse duration One millionth less of a second cost inexpensive Reliable

Mode locking 10(12)watts more Femto to pico seconds expensive Difficult to maintain

Indications of ND:YAG laserCapsulotomy Iridotomy laser trabeculoplasty(532nm) Selective laser

trabeculoplasty(532nm) Management of diabetic retinopathy(532 nm) Perilenticular membrane disruption Removal of deposits from IOL surface(YAG sweeping) cyclophotocoagulation

Laser suturolysis,in trabeculectomy Bleb remodelling in overfiltering bleb Goniopuncture Deep sclerectomy Treatment of Persistent pupillary membrane Pupilloplasty Anterior hyloidotomy Vitreous strand lysis in cataract wound Iridolenticular synaecholysis

Excimer laserArgon

flouride laser(193nm,UV region) Emits photons with an energy of 6.5 eV,capable of breaking intramolecular C-C (3.6eV),CN(3.1eV),C-H(4.3eV)bonds. When the concentration of the photons exceeds a critical value, the broken intramolecular bonds can no longer recombine. To make accurate corneal lesions.

INDICATIONS OF EXCIMER LASER

LASIK-myopia(-1to -15D),hypermetropia(+1 to +8 D) astigmatism(-5 to 10 D) Femto-LASIK Customized wavefront guided LASIK PRK LASEK LASER surgery for presbyopia PTK(Phototherapeutic keratectomy) Excimer laser assisted deep sclerectomy Excimer laser trabeculectomy

Argon laserGas

laser(PHOTOCOAGULATION) 514 nm wavelength(visible) INDICATIONS Argon laser trabeculoplasty Argon laser peripheral iridoplasty Diabetic retinopathy Macular edema CRVO/BRVO

Eales

disease Central serous chorioretinopathy ARMD Miscellaneous-sickle cell retinopathy,coats disease,retinal breaks,tumours Treatment of trichiasis Punctal occlusion in dry eye Endoscopic DCR

CO2 laser10,6oonm(IR) photovapourization

Intraocular photocautery-malignant intraocular tumours Filtering procedures(especially for neovascular glaucoma)-pulsed focussed beam,400-500micron spot Adnexal uses-removal of capillary hemangiomas,lid lesions(seborrhoeic keratitis) Blepharoplasty(6watt,0.1 mm spot),orbitotomies Endonasal DCR

ADVANTAGE Adjacent blood vessels are also treated resulting in

Diode laser750-950

nm(near infrared)

INDICATIONS :

Retinal

photocoagulation Transpupillary thermotherapy Trabeculoplasty Cyclophotocoagulation DCR

Advantages of diode laserLack

of laser flash, Portable, No special electrical/cooling system, Less breakdown of blood retinal barrier, No blue light hazard, Ability to penetrate through cataractous lens, Ability to penetrate through haemorrhage.

Disadvantage of diode laserBleeding

stumps cannot be coagulated since hemoglobin is not absorbed in infrared region.

Complications of lasers in ophthalmology

Bleeding Increased in pressure within the eye Clouding of the cornea Inadvertent corneal burns

Contraindications to lasers in ophthalmology Cognitive difficulties /unreliable patient Areas of haemorrhage Increased sensitivity to light(Pts of

porphyria) Epileptic patients Patients on immunosuppressive drugs Uncontrolled diabetes/vascular disease/autoimmune disease Pregnancy/nursing Progressive refractive error Herpetic infection in the past Severe dry eye Active/residual systemic disease affecting wound healing

I II IIa IIIa IIIb IV

SAFE Low CD players Not 1 mw Laser pointers intended to 1MW, Laser scanners be viewed 1000sec or firearms Hazard if Less than collected equal to Hazard if 5-500 mw anddirect or 5 mw than Medical,scientific, the Direct and More focussed in 500 reflected industrial,military eye is beam exposure mw,1/10th lasers viewed of asecond

Safety check listAppropriate

warning signs posted. Access to laser and treatment area is secure and controlled. Inspect laser for proper functioning. Visually inspect and clean safety goggles. Laser injury management protocol. NEVER

UNDER ANY CIRCUMSTANCES LOOK INTO ANY LASER BEAM

Laser procedures( under evaluation)Penetrating keratoplasty with non contact trephining Lamellar keratoplasty Laser asepsis(healing of corneal ulcer)argon laser Removal of lens-photoablation and photofragmentation(Nd: YAG laser) Laser scleral buckling-holmium yag laser Vitrectomy-pulsed erbium yag laser Drainage of subretinal fluid-argon laser Phototherapy-neovascular stimulation,aseptic phototherapy

Advantages of lasersqPainless procedure qDry surgical field qNo risk of infection qLess time qOutpatient basis qConvenient qPrecise qSafe

Disadvantages of lasersExpensive Equipment Repeatability

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