1. LASERS IN OPHTHALMOLOGY
Dr Rashmi Amarnath
Minto Regional Institute of Ophthalmology

2. Lasers in Ophthalmology
1917- Einstein proposed the theory of stimulated emission
Light Amplification by Stimulated Emission of Radiation
Ruby laser in Theodore Maiman

3. Terminology Stimulated Emission Light Amplification
Population Inversion

4. Laser Physics
When electrons from higher energy fall back to lower orbital energy levels, they emit photons- stimulated emission.

5. Components of Laser Activated medium Energy pumping source
Resonant cavity for oscillation

6. Properties of Laser
Monochromacity- allows selection of particualr wavelength
Coherence- Spatial and temporal coherence
Directionality- highly collimated beam for focussing
Polarization- max energy transmission without loss due to reflection
Brightness- Power/unit area /solid angle

7. Laser output
Continous mode: Continous output, externally controlled, has uniform power
Pulse mode: Concentrated energy, delivered over short period
Q switched lasers: Intracavitary shutter allows rapid energy release, short high power pulse
Mode locking: Ultra short pulses in pico seconds

8. Laser tissue interaction
Photochemical reactions:
PDT, Photoablation by EXIMER
Mechanical effect:
Photodisruption Nd-YAG.
Photothermal:
Photocoagulation , Photovaporization

9. Types of lasers Gas : Semiconductor diode laser/Solid state: Nd-YAG
Noble gases- argon, krypton
Molecular gases- CO2, N2
Dimer- EXIMER
Semiconductor diode laser/Solid state: Nd-YAG
Dye tunable:

10. Absorption spectrum in ocular tissues

11. Absorption spectrum of ocular tissues
Melanin absorption in nm
Deoxyhemoglobin 555nm
Oxyhemoglobin 542nm, 577nm
Xanthophyll <500nm

12. Lasers in posterior segment diseases
Argon green
Krypton red
Frequency doubled Nd Yag laser
Diode laser,
Dye laser,

13. Indications for Laser Diabetic retinopathy Retinal breaks
PDR, macular edema
Retinal breaks
Neovascularization- CRVO, Sickle cell retinopathy
Macular edema
CSR
SRNVM
Leaking aneurysm- Coats, VHL, retinal macroaneurysm

14. PRP in diabetic retinopathy
Inferior quadrant covered first
Focal laser first if associated macular edema present
From arcades to equator
1DD nasal to disc
Completed in 2-3 sittings.
Fill in laser for periphery if NVE does not regress

15. Mechanism of action in PRP
>1200 spots, um, mW
Produces photocoagulation of proteins resulting in adhesion of chorioretinal lasers
Decreases release of hypoxic factors
Produces decreased consumption of nutrients in peripheral retina

17. Mechanism in macular edema
Focal laser: um,
Duration : 0.1s
Coagulation of all leaking microaneurysm u from center
Enhances the RPE pump
Grid Laser: 100um,
Duration: 0.1s
Decreases edema

18. Mechanism in prophylaxsis of retinal breaks
Barrage laser: um, mW
3-4 rows around break
Produces chorioretinal adhesion

19. CNVM

20. PDT 689 nm solid state laser
Spot size- GLD+1000 microns(max spot size is 6400 microns)
Intensity-600Mw/sq cm
Power-50 J/sq cm
Duration-83 seconds

21. Mechanism in PDT
Verteporfin dye is absorbed by LDL receptors present in the CNVM
These porphyrins absorb Laser light and are promoted to their excited triplet state (free radicals, singlet oxygen)
Free radicals lead to local molecular and cellular injury

22. Wet AMD - TTT Treatment of Subfoveal Occult CNV
Choroid
RPE
Retina
Bruch’s Membrane
Eyes with symptomatic subfoveal occult CNV
Occult defined as fibrovascular RPE detachments
and late leakage of undetermined source

23. Mechanism in TTT
Low energy, longer duration laser acts on chorioretinal layer producing photochemical reaction
810nm, large spot light adapter

24. Complications of Laser
Decreased color vision
Decreased contrast
Decreased field of vision (PRP)
Accidental foveal burns
CNVM
Vitreous hemorrhage
Retinal holes

25. Laser Hazards Ophthalmic Lasers are grade IV biological hazard
Indicator board
Antireflection coating of lens, slit lamp
Use of protective glasses by surrounding personnel

26. THANK YOU