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Lasers in ophthalmology
- 1. PRESENTER:DR NIKITA JAISWAL Resident IMS & SUM HOSPITAL
- 2. ο ο In 1916, ALBERT EINSTEIN laid the foundation for invention of laser ο Laser was coined by GURDEN GOULD. ο The first working laser in ophthalmology was made by THEODORE MAIMAN,1960. ο He utilized a pulsed ruby laser coupled with a monocular direct ophthalmoscopic delivery system. HISTORY:
- 3. ο ο INTRODUCTION ο PROPERTIES ο TYPES ο APPLICATIONS GLOSSARY
- 4. ο L: LIGHT A: AMPLIFIED BY S: STIMULATED E: EMISSION R: RADIATION
- 5. ο PROPERTIES: ο Coherence: wavelengths of the laser light are in phase in space and time. ο Monochromatic light : beam of single wavelength. ο Collimation: all rays are parallel to each other. INTRODUCTION
- 6. ο
- 7. ο Genesis
- 8. ο
- 9. ο
- 10. ο
- 11. ο
- 13. οlight Barely visible retinal blanching mild Faint white retinal burn Moderate Opaque,dirty white retinal burn heavy Dense-white retinal burn Burn intensity
- 14. ο
- 15. ο
- 16. ο ο Solid state:ruby,Nd:yag ο Gas lasers: argon,krypton,neon,helium ο Excimer: argon fluoride Types:
- 17. ο Light tissue interactions: Photocoagulation Photodisruption Photoablation photoactivation
- 18. ο ο Laser light is absorbed by the RPE & then it produces heat which denatures the proteins. ο Light energy applied to tissue changes to thermal energy βtissue temperature rises by 65βc which causes coagulative necrosis. ο This heat coagulate the pigmented & adjacent tissues. ο The outer layers are more effected than the inner layers. Photocoagulation:
- 19. ο ο Green argon laser (514.5 nm) ο Freq doubled Nd:YAG laser (532 nm) ο Krypton red laser (647nm) ο Diode laser(810nm) Types of lasers in photocoagulation
- 20. ο ο Absorbed selectively at the RPE, Hb pigments,choriocapillaries,layer of rods & cones, outer & inner nuclear layers. ο Readily absorbed by the melanin granules. ο Coagulates from choriocapillaries to INL. Argon green laser
- 21. ο ο Produces a pea green beam. ο Often termed as βgreen laserβ/ktp laser. ο Highly absorbed by Hb & the melanin pigment. ο It coagulates from choriocapillaries to ONL. ο It causes coagulation with least energy transmission & shows considerable safety in macular treatment. Freq-doubled Nd:YAG laser
- 22. ο ο Melanin absorbs it readily. ο It is not absorbed by xanthophylls & Hb & thus it is particularly suitable for macular photocoagulation. ο It coagulates deeper into the RPE & choroids. It has insignificant effect on the vascular system of retina. ο It is less absorbed & more highly transmitted through RPE Krypton red laser (647nm)
- 23. ο ο The energy produced is released in a very short time. ο The laser beam is focused, concentrating the power into small area ο It produces a spark & an acoustic waveβwhich disrupts the tissue. ο ex:Nd:YAG laser. Photodisruption:
- 24. ο ο It is a conversion of chemical from one form to another by light. ο ex-the use of verteporfin βa drug that is chemically inert but is activated by light ,after which it destroys neovascular tissue. Photoactivation
- 25. ο lasers Wavelength Diode 810 nm Krypton red 647 nm Krypton yellow 568 nm Frequency doubled Nd YAG 532 nm Argon green 514 nm Argon blue 485 nm
- 26. ο OCULAR TISSUES LIGHT ABSORBED LIGHT PASSED MELANIN GREEN,YELLOW,RED & INFRAREDS XANTHOPHYLL BLUE YELLOW & RED HAEMOGLOBIN BLUE, GREEN & YELLOW RED
- 27. ο Indirect ophthalmoscope Slit lamp biomicroscope Endophotocoagulation Laser delivery systems:
- 28. ο
- 29. ο At our setup
- 30. ο
- 31. ο
- 32. ο ο Anaesthesia:topical,peribulbar/retrobulbar ο Lenses:2 types of contact lenses 1-negative-power planoconcave lenses. 2-high-plus-power lenses. Practical aspects of laser photocoagulation 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.
- 33. ο ο Focused on the degree to which photocoagulation must be targeted to a particualr tissue sparing the normal tissue. ο Area directly related to intensity & duration of irradiation. Choice of laser wavelength: Lasers characteristic Preferred Green laser Absrbed 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
- 34. ο ο Gas laser ο Mechanism: PHOTOCOAGULATION ο 514.5 nm wavelength(visible) INDICATIONS ο Diabetic retinopathy ο Macular edema ο CRVO/BRVO ο Eales disease ο sickle cell retinopathy,coats disease PRP
- 36. ο
- 37. ο ο 3 SITTINGS ο INTERVAL 1-3 WEEKS ο 1800 applications of 500 Β΅m retinal spot size,0.1 to 0.2 sec duration (180mw to start with) SITTING: SESSION SPOT SIZE POWER EXPOSURE 1ST 100-200Β΅m 100-400mw 0.05-0.2 sec 2ND 300-500Β΅m 400-800 mw 0.1-0.2 sec 3RD 300-500 Β΅m 400-800 mw 0.1-0.2 sec
- 38. ο Modertae to heavy laser burns Laser in PRP
- 39. ο
- 40. ο
- 41. ο FOCAL PHOTOCOAGULATION: SPOT SIZE EXPOSURE POWER 50-100Β΅m 0.1 SEC 100-400mw : Areas 5oo Β΅m away from disc margin & centre of macula but within within 3000Β΅m
- 42. ο ο Paracentral scotoma ο Transient increase of edema ο Photocoagulation scar expansion ο Subretinal fibrosis at laser site ο Inadvertent foveolar burns complications
- 43. ο 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 50-200Β΅m 0.1 sec 50-100mw Lasers used:- argon green & yellow
- 44. ο
- 45. ο ο This is done in single spots with pulse durations of 10 to 20 ms rather than conventional 100-200 ms ο Multispot laser delivers multiple uniform laser burns simultaneously by a single foot pedal depression in a variety of pattern. ο Patterns are:- Pattern scan laser: Pattern Retina Macula Square arrays 5*5 Arcs Concentric rows varying from 1 to 3 Exclusion zone upto 2mm circular For small hole
- 46. ο ο The spot size is restricted (100,200& 400micron) ο Inability to design the pattern ο It produces some more noise. ο Difficulty in penetration through media opacities. Disadvantages
- 47. ο ο This was invented by pankratov in 1990 in this the laser energy in short-pulse or in micropulse. ο Parameters:- retinal spot size,laser energy & duration constant, size of retinal lesion is governed by DUTY CYCLE. ο Longer the OFF time between pulses lesse will be the duty cycle= less damage to tissue & less heat produced. Micropulse laser: Cumulative refraction time between pulses.
- 48. ο