Podcast
Questions and Answers
What happens to the collagen fibers when the temperature reaches close to 70°C during photocoagulation?
What happens to the collagen fibers when the temperature reaches close to 70°C during photocoagulation?
What is the primary goal of selective photothermolysis?
What is the primary goal of selective photothermolysis?
What happens to the tissue if the temperature is increased past 100°C?
What happens to the tissue if the temperature is increased past 100°C?
What is photovaporization used to treat?
What is photovaporization used to treat?
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What is the term for the conduction of heat into the surrounding tissue?
What is the term for the conduction of heat into the surrounding tissue?
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What is the result of dimerization?
What is the result of dimerization?
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What is the formula to calculate energy in Watts?
What is the formula to calculate energy in Watts?
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What is the main difference between laser light and light bulb light?
What is the main difference between laser light and light bulb light?
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What is the wavelength range of visible light?
What is the wavelength range of visible light?
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What is the type of scattering that occurs in blue eyes?
What is the type of scattering that occurs in blue eyes?
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What is the main property of laser light that makes it useful for ophthalmic treatment?
What is the main property of laser light that makes it useful for ophthalmic treatment?
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What is the type of light that is most absorbed by the skin?
What is the type of light that is most absorbed by the skin?
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What is the mechanism of damage caused by laser light?
What is the mechanism of damage caused by laser light?
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What is the result of increasing the temperature of tissue by 10-20°C?
What is the result of increasing the temperature of tissue by 10-20°C?
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What is the wavelength range of UV-B light?
What is the wavelength range of UV-B light?
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What is the type of light that is most absorbed by melanin?
What is the type of light that is most absorbed by melanin?
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Study Notes
Laser Properties
- Velocity of light = frequency x wavelength
- Energy (Watts) = 6.63 x 10^34 x frequency
- F = velocity of light in air in a vacuum / L (where L is the wavelength)
Laser Characteristics
- Monochromatic (one color)
- Thin beam (collimated)
- Coherent (in phase waves)
- Can focus into the same point
- Much more intense than regular bulb light
Laser Applications in Ophthalmic Treatment
- Color is important (monochromatic)
- Collimated is necessary to focus the light
- Has a specific focus point
Light Spectrum
- UV (100 nm - 400 nm): UV-C (100 nm - 280 nm), UV-B (280 nm - 315 nm), UV-A (315 nm - 400 nm)
- Visible light (400 nm - 760 nm): blue (400 nm - 500 nm), green (500 nm - 550 nm), yellow (550 nm - 590 nm), orange (590 nm - 620 nm), red (620 nm - 760 nm)
- IR (760 nm - 1 million nm): IR-A (760 nm - 1400 nm), IR-B (1400 nm - 3000 nm), IR-C (3000 nm - 1 million nm)
Scattering
- Scattering is the result of eye color
- Raleigh scattering: occurs when light encounters small molecules (e.g., blue eyes)
- Mie scattering: occurs when light encounters larger particles (e.g., collagen fibers)
Eye Color Determinants
- Blue eyes: lack of pigment in the iris stroma, Raleigh scattering
- Green eyes: some pigment in the iris stroma, scattering by collagen fibers
- Brown eyes: dense pigment in the iris stroma, absorption of light
- Grey eyes: large collagen molecules in the stroma, Mie scattering
Light Absorption
- Tissues with nucleic acids and amino acids absorb UV-C light
- Skin and eye pigment (melanin) absorb UV light well
- Macular pigment absorbs blue light
- Hemoglobin absorbs visible light in the order of blue, green, yellow, and red
- Cornea absorbs UV-C, IR-C, UV-B, IR-B, and very little IR-A and UV-A
- Lens absorbs UV-B and UV-A
- Retina absorbs IR-A light
Damage Mechanism
- Photothermal: heat involved, temperature increase causes tissue damage
- Photochemical: light triggers chemical reactions
- Photomechanical: light causes mechanical damage (e.g., ionization, photo destruction)
Photoscoagulation
- Increasing temperature causes denaturation of proteins, coagulation, and cell shrinkage
- Diabetic retinopathy treatment involves coagulation of the retina
- Shortening of collagen fibers occurs between 50-70°C
- Temperature increase above 100°C causes water content in tissue to explode (photovaporization)
- Extreme temperatures (150°C) cause carbonization of tissue (photocarbonization)
- Melting occurs at 300°C
Thermal Damage
- Heat conduction, exposure time, thermal relaxation time, and spot size affect thermal damage
- Selective photothermolysis reduces collateral damage by controlling these factors
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Description
This quiz covers the fundamental concepts of light, including velocity, frequency, wavelength, and energy. It also explores the differences between laser light and light bulb light, including color and beam type.
