DIS - Eye Trauma IV: Radiation - Week 8 Flashcards
True or false
Artificial sources tend to emit radiation in excess of the suns radiation.
True
What two gases are responsible for absorbing most of the UV radiation from the sun? List three other important componrnts and what they absorb.
Oxygen gas and ozone
H2O, CO2, and dust help absorb some infrared
In terms of damage to tissue, what does the effect of EM radiation depend on (2)?
Wavelength and photon energy
What are the two distinct damage mechanisms of EM radiation? Note the wavelengths that generally cause each.
Thermal -long wavelengths, low photon energy -causes molecular agitation Photochemical -short wavelengths, high photon energy -causes excitation, breaking chemical bonds
At what energy levels does ionisation begin to occur?
> 6eV
Note what wavelengths the following structures absorb (at ~90% transmittance): Cornea Aqueous Lens Vitreous
Cornea ~350nm
Aqueous ~400nm
Lens ~450nm
Vitreous ~500nm
What ocular structures absorb UVB and UVC (1)?
The cornea
What ocular structures absorb UVA (2)?
The lens and iris
What ocular structures absorb IRC (1)?
The cornea
What is the range of UV light? Note the range for each subcategory.
200nm to 400nm
UVA - 315nm to 400nm
UVB - 280nm to 315nm
UVC - 200nm to 280nm
List 7 common sources of UV light.
The sun Germicidal lamps High pressure mercury arc lamps Special fluorescent lamps Welding arcs Sunlamps Sunbeds
What radiation does the tear film generally absorb?
Some UVC
Wjat radiation do the cornea and conjunctiva absorb (2)? What does the anterior stroma absorb specifically?
UVB and UVC
Anterior stroma absorbs UVB
What radiation does the aqueous absorb (2)?
UVA and UVB
What radiation does the lens nucleus and epithelium absorb (3)?
UVA, some UVB, and some visible light
What radiation does the lens capsule absorb?
Negligible amounts
What ocular structure absorbs most UV radiation? Where is damage due to radiation usually limited to?
Corneal epithelium
-damage usually limited to this layer
What occurs with photokeratitis and does exposure have a cumulative effect? Who is it common amongst and what is it often referred to as (3)?
Reduced cell division, cell death and/or ulceration
Exposure has a cumulative effect
Also known as arc eye, welders flash, and snow blindness
How long does the latent period of photokeratitis last for? List 5 symptoms and note when discomfort disappears.
Latent period of 6 to 12h FB sensation Photophobia Lacrimation Blepharospasm Lid oedema Discomfort disappears in 48h
List 8 ocular signs of ultraviolet light radiation.
Lid oedema Blepharospasm Lacrimation Oedema Photophobia Corneal erosions Hyperaema Erythema
List 6 components of assessing damage due to ultraviolet light.
History VA Slit lamp (lid eversion and staining) AC DFE Photo
What are the goals of managemeny for damage due to ultraviolet light? List 2 treatment options, noting dosages.
Prevent infection
Alleviate pain
Facilitate healing
Non-preserved tear supplements
-q5-10 mins for the first hour, then q1h to q3h
-broad spectrum antibiotic gtt (usually not needed)
List 5 long term effects of UV radiation on the anterior eye.
Pterygium Pingueculum Nodular band-shaped keratopathy (climatic droplet keratopathy) Cataracts Tumours
Is nodular band-shaped keratopathy a degenerative condition? What is the pathophysiology and does it begin peripherally or centrally?
Is degenerative
Accumulation of translucent material in superficial corneal corneal stroma within the interpalpebral region
Begins peripherally and spreads centrally
Which type of UV light causes cataract?
UVB
Is the retina protected in aphakes?
No
Does UV exposure increase incidence of ARMD?
Some studies found it does
One found no association
Describe how solar maculopathy occurs. Can small sungazes cause damage or is a long period required? What increases incidence (2)? Who is it most common amongst (3)?
A burn to the foveal area due to excess UV light
Sungazing for even 20 seconds can cause damage in some patients
Much higher incidence if solar eclipse or binocular/telescope use
Most common in drug users, alcoholics, and mentally unwell patients
What is the range of visible light?
400nm to 780nm
Does visible light cause photochemical or thermal damage to the eye, or no damage at all (2)?
Mostly photochemical damage
Even low levels can cause damage to PR and RPE
Thermal photocoagulation - occurs when high intensity light is focused on the retina
Is there any evidence to suggest limiting blue light exposure is beneficial?
No
What is the range of infrared light? Note the three categories.
780 to 10,000nm
IRA
IRB
IRC
List 5 common sources of infrared light.
Sunlight Arc lamps Electrical fires Glass and steel furnaces Welding
Note what infrared light the following structures absorb.
Cornea (1)
Lens (2)
Retina (1)
Cornea - IRC
Lens - IRB, IRA
Retina - IRA
Give two corneal effects due to infrared exposure.
Opacification
Polymegathism
What effect does indirect exposure of infrared light have on the lens and via what structure?
Anterior capsular cataract via inditect hrat transfer from the iris pigmented epithelium, which absorbs the light
What effect does direct exposure of infrared light have on the lens (4)?
Posterior subcapsular cataract
Posterior cortical cataract
Cortex opacification
Lamellar splitting and exfoliation of the anterior capsule
List 5 causes of retinal damage due to infrared exposure. What absorbs the infrared (2)?
Solar retinopathy
IR laser
Metal-arc inert gas welder
High intensity light sources (xenon gas lamps)
Medical lasers
-absorbed by melanin granules in the RPE and choroid
What is the primary effect of microwaves and what ocular structure is particularly susceptible to it and why?
Increased tissue temperature
Lens particularly susceptible
-avascular
-cant dissipate heat
What does the degree of microwave penetration depend on?
Wavelength
What generally occurs when microwaves are applied to the lens and is it supported by epidemiology?
Posterior subcapsular cataracts in animal models
-nkt supported by epidemiology
Briefly describe how a laser works.
Radiant energy is used to excite atoms, where electrons move to a higher energy level
As they return, they emit a specific energy of light
What are two ocular effects of UV laser exposure? What about visible and IR lasers?
UV -corneal epithelial damage -cataracts IR -traumatic cataracts
What mode of lasers can cause shockwaves?
Q switched high intensity beams
List the four main classes of lasers and note which two can cause permanent damage.
1 and 1M 2 and 2M 3R and 3B 4 3B and 4 can cause irreversible damage
What is ionising radiation? Give four examples.
Very short wavelengths
- cosmic rays
- radioisotopes
- xrays
- gamma rays
Is daamage due to ionising radiation initially severe?
No
Lisr four signs of ionising radiation damage.
Erythema
Skin damage
Corneal compromise
Cataracts
Do thermal injuries to the eye often involve the globe? Explain.
No, mostly lids
Protected by blink reflex
List three characteristics of ocular thermal injury.
Marked oedema
Tissue necrosis
Pain
Is the globe commonly or rarely involved in flame burn injuries?
Rarely
Why may epiphora occur with a flame burn injury?
Blocked puncta due to subsequent fibrosis
Where do contact burns most often occur?
90% at home
What is the management of a thermal burn (6)?
Clean and irrigate the site Debride necrotic tissue Prophylaxis and cold compresses Antibiotic q2g for 1 day then q4h until healed 1 drop homatropine in office Non-preserved tear supplements prn Analgaesic (panadol forte)
