Lasers In Ophthalmology Part -1

LASERS IN OPHTHALMOLOGY PART -1 DR. BHARTI AHUJA

INTRODUCTION A “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’. 

HISTORY In

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 LASERS MONOCHROMATIC DIRECTIONAL COHERENCE-spatial

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

La se r –tissu e in te ra ctio n s

p h o to th e rm a l

p h o to ch e m ica l

P h o to co a g u la tio n / P h o to va p o riza tio n p h o to ca rb o n iza tio n

M e ch a n ica l / p h o to io n iza tio n

p h o to d isru p tio n

P h o to ra d ia tio n / p h o to a b la tio n

PHOTOTHERMAL EFFECTS 

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

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Visible and infrared wavelengths.

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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 tissues Melanin(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 ig h e r e n e rg y la se r lig h t a b so rb e d b y ta rg e t tissu e re su ltin g V a p o riza tio n o f b o th in tra a n d extra ce llu la r w a te r.

W h e n th e lo ca l sto re o f w a te r is va p o rize d , th e n ca rb o n iza tio O ccu rs.

C O 2 LA S E R ( IR w a ve le n g th )

PHOTOCHEMICAL EFEECTS photoradiation./ PHOTODYNAMIC 

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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

photoablation

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High 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.

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Exposure time is shorter(nanoseconds) Excimer lasers

PHOTOIONIZATION/MECHANIC AL EFFECTS 

Photodisruption-high energy laser light deposited 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.

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Infra red wavelengths,1064 nm(Nd:YAG)

SOLID STATE LASING Crystals material containin g rare earth

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

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

Laser output Continuous/constant amplitude/cw 

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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

Single pulsed

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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

Laser parameters Exposure

time(0.1-0.2 sec)

Power Spot

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

Laser lenses in photocoagulation Planoconcave

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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

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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)

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Diagnostic applications Scanning

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 tomography It

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

Wavefront analysis It

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 up History

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

Nd:YAG LASER qSolid state(PHOTODISRUPTION) Wavelength (1064nm,IR region) Invisible pulses,red aiming beam. Q switch

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power

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

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

Indications of ND:YAG laser Capsulotomy 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 

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Excimer laser Argon

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 

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Argon laser Gas

laser(PHOTOCOAGULATION) 514 nm wavelength(visible) 

INDICATIONS Argon laser trabeculoplasty Argon laser peripheral iridoplasty Diabetic retinopathy Macular edema CRVO/BRVO 

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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 laser 10,6oonm(IR)  photovapourization 

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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 

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ADVANTAGE  Adjacent blood vessels are also treated resulting in 

Diode laser 750-950

nm(near infrared)

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INDICATIONS :

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Retinal

photocoagulation Transpupillary thermotherapy Trabeculoplasty Cyclophotocoagulation DCR  

Advantages of diode laser Lack

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 laser Bleeding

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

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Complications of lasers in ophthalmology

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Bleeding

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Increased in pressure within the eye

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Clouding of the cornea

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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 Hazard if Less than or firearms collectedif 5-500 equal to Hazard mw and mw than Medical,scientific, the direct Direct andor 5More focussed reflected in 500 industrial,military eye beam is exposure mw,1/10th lasers viewed of asecond

Safety check list Appropriate

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 

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

Disadvantages of lasers Expensive Equipment Repeatability 

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Thank you