Lasers

Question 1

Lasers

Answer 1

Light Amplification by Stimualted Emission of Radiation

Question 2

What is collimated light

Answer 2

Waves are in parall

Question 3

What is coherent light

Answer 3

Waves are all in phase and have same wavelength

Question 4

When can resonance occur?

Answer 4

Mirrors placed at a distance apart that is a multiple of the wavelength.

Resulting light is exactly in phase and reinforces itself

Light becomes stronger and stronger while remaining in phase

Question 5

Features of light from laser

Answer 5

Coherent (in phase)
Monochromatic (one wavelength)
Collimated (parallel rays)

Question 6

How can laser damage occur?

Answer 6

Thermal
Ionization
Photochemical

Question 7

How does thermal laser damage occur

Answer 7

Depends on pigment present
Melanin absorbs most of the visible spectrum of light

Xanthophyll at macula absorbs blue light and shorter wavelengths

Haemoglobin absorbs blue,green,yellow light

Photocoagulation avoids shorter wavelengthsWh

Question 8

ich colour laser in the eye

Answer 8

Red or green longer wavelegths to avoid damage to macula pigment

Question 9

How does ionizing laser damage occur

Answer 9

Photon energy strips electrons from molecules forming ions

IOns form a plasma that displaces tissue

NdYAG and argofluoride laserW

Question 10

What are photochemical effects of laser

Answer 10

Pulse duration > 10secs
Free radicals formed toxic to cells

Short wavelengths cause damage at lower levels of irradiance and so more harmful

Question 11

Argon laser wavelegths

Answer 11

Blue 488nm
Green 514nm

Blue light absorbed by xanthophylls in inner layer of macula - contraindicated

Question 12

He:Ne gas laser

Answer 12

633nm
Visible red light
Aiming beam for lasers with invisible output

Question 13

Diode laser

Answer 13

810nm infrared
Continuous wave mode

Absorbed by melanin\REtinal photocoagulation
Photocycloablation for glaucoma - penetrates sclera

Question 14

NgYAG laser

Answer 14

1064nm infrared

Continuous wave laser that is Q switched and is often used to perform capsulotomy

He:Ne laser produces red aiming beam

Question 15

Excimer laser

Answer 15

Argon-fluorine dimer laser to emin 193nm UV radiation

Absorbed by cornea and causes tissue removal

Photorefractive keratectomy, laser intrastromal keratomileusis, phototherapeutic keratectomy

Question 16

What is confocal microscopy used for?

Answer 16

View layers of the cornea

Question 17

How does OCT work

Answer 17

Using near infrared light

Optical beam of light directed at tissue results in most of the light scattering

Small amount of light is reflected

Scattered light does not contribute to the image but produces glare

Interferometer uses superimposition to combine separate coherent light waves together so that combination has constructive or destructive interference to distinguish scattered light from reflexted light

3D image from optical scattering media

Question 18

What is class 1 laser safet

Answer 18

Safe, light contained in enclosure

CD player

Question 19

Class 2 laser safety

Answer 19

Safe during normal use

Laser pointer

Question 20

Class 3a

Answer 20

Small risk of damage within the time of the blink reflex

5mW

Question 21

Class 3b

Answer 21

May cause severe eye damage on exposure

CD writer 500mW

Question 22

Class 4

Answer 22

Can burn skin and cause eye damage

Industrial, scientific

Question 23

Complications of Nd:YAG capsulotomy

Answer 23

LEns pitting, sublaxation
Iritis
Raised IOP
Retinal break
Macula oedema

Question 24

Which laser for retinal photocoagulation in vitreous haemorrhage or dense cataract

Answer 24

Krypton Red - penetrates cataract and VH better