Effects of radiation and glare on human eyes

EFFECTS
OF
RADIATION
AND
GLARE ON EYE

Amrit Pokharel
B Opt0metry, IIIrd year

Radiation???

 Radiation is an energy in the form of electro-
magnetic waves or particulate matter, traveling
in the air.

Glare???
 A relatively bright light that produces
 Unpleasant or discomfort
 A temporary blurring of vision, or

 A feeling of ocular fatigue

 Which interferes with vision

Consequence?
 The only real consequence
 Is the reduction in the quality of an image

 Any problem in
 Corneal layers
 Lens

 Viterous, or
 Retina

Results into GLARE

Electromagnetic Spectrum

8 5/16/2012

ULTRA-
VIOLET
RADIATION

FG Figure 7-2

9 5/16/2012


ULTRA-
INFRARED
VIOLET RADIATION
RADIATION

FG Figure 7-2

10 5/16/2012

Types:
 Ionizing Radiation

 Non-ionizing Radiation

Ionizing Radiation
 Definition

“It is a type of radiation that is able to disrupt
atoms and molecules on which they pass
through, giving rise to ions and free radicals”.

Ionizing Radiation
 Caused by the disintegration of atoms
 With the subsequent release of subatomic
paricles
 The energy released is SO HIGH that the
binding energy of the electron is broken down
 And then comes off an ejection of electrons,
leaving behind a positively charged atom
called cation

Radioactive Atom Ionizing Radiation

alpha particle
X-ray

beta particle

gamma ray

Ionizing Radiation

Paper Wood Concrete Energy
Alpha
Low
Beta
Medium

Gamma
High

How radiation brings about
change…

Effect
 Draper’s law
 Damage depends on:
 Exposure time
 Concentration

 Type

 Direct effect
 Cellular anomalies or death

Effect
 Indirect effect
 Damage to blood vessels

 Low levels of radiation
 Engorged conjunctival vessels
 Loss of corneal lustre

Effect
 High levels of radiation
 Exfoliation of epithelial cells
 Keratitis

 Corneal ulcer
 Cataract

 Retinal degeneration

Non ionizing Radiation
 Definition

“ They are electromagnetic waves incapable of
producing ions while passing through matter,
due to their lower energy.”

 The radiation energy is lower than the binding
energy of the electron

 Only states change
 Ground ---excited


 The change to the irradiated is brought about
as:
 Thermal Effect

 Photochemical Effect

 Photoluminescence(fluorescence)

 Thermal Effect:
 Heating effect
 d/t the change in energy states of atoms

 Solar retinopathy is an example that involves a
thermal lesion

 Solar retinopathy
 Pathogenesis:
thermal effects of
solar radiation by
directly or indirectly
viewing the sun
 Presentation is
within 1-4 hours of
solar exposure with
unilateral or bilateral
impairment of central
vision and central
positive scotoma

 Solar retinopathy
 VA is variable
 Fundus: a small
yellow or red
foveolar spot that
fades within a few
weeks
 The spot is replaced
by a sharply defined
foveolar defect with
irregular borders or
a lamellar hole

 Photochemical Effect:
 When the radiant energy is absorbed, the
molecule that absorbs may decompose or
chemically react to produce a unique chemical
product.

 Photokeratitis is an example that involves a
thermal lesion

Photokeratitis
 Damage to the corneal epithelium
 Due to the absorption of UV-rays below 300nm
 Also called
 Photophthalmia

 Photoconjunctivitis

 The damage tends to be cumulative

Photokeratitis
 Pathogenesis:
• After 4-5 hrs(latent period)of
UV exposure

• There occurs desquamation
of corneal epithelium

• Leading to the formation of
multiple epithelial erosions

Photokeratitis
 The patients experiences:
 Foreign body sensation

 Photophobia

 Lacrimation

 Blepharospasm

 Redness

 Oedema

Photokeratitis
 The above clinical picture is also seen in
SNOW BLINDNESS

 Occurs due to exposure to UV radiation from
large areas from snow

 Also found in Welder’s keratitis in welders who
strike an arc before they wear a protective
helmet

Photokeratitis
 Prophylaxis:
 Crooker’s glass
 Itcuts off all the UV- and IR- rays
 To be used by those who are prone to the radiation
hazard
 Cinema operators, welding workers

Photokeratitis
 Treatment:
 Cold compresses

 Pad, bandage and antibiotic ointment for 24 hours

 Oral analgesics

Photokeratitis
 Photoluminescence (fluorescence):
 Asthe property of fluorescence in inherent to the
lens, the lens is capable of absorbing UV rays

 Thisabsorption gives off the formation of
material-fluoregens, that give the characterstic
colouration(yellowish) to the lens.

Concentration of the radiant
energy by the eye

Transmission of the spectrum
 Cornea: 270nm-3000nm

 Aqueous: 290nm-2700nm

 Lens: 310nm(375nm old)-2500nm

 Vitreous: 290nm-1600nm

Absorption of the spectrum
 Tear layer:
 Absorbs only a small amount of radiation
 Absorbs UV below 290 and IR above 3000

 Cornea:
 Has a similar absorption band
 But partially transmits UV from 290 to 315 and IR
from 1000 to 3000

 Aqueous humour:
 Absorbs very little or no radiation at all
 Lens:
 The lens of a child absorbs UV below 310nm and
IR above 2500nm
 The lens of an older adult absorbs almost all
radiation below 375nm and therefore transmits
very little UV radiation
 No change in the IR absorption band with
increasing age

 Vitreous:
 Absorbs radiation below 290nm and above
1600nm

The retina receives the radiation transmitted by
the vitreous. UV radiation received by the
retina decreases with age

Effects of Ultraviolet radiation

 Photophthalmia

 Pterygium

 Pingueculum

 Cataract

 Band-shaped keratopathy

 Macular degeneration

 Pterygium
A triangular fibro-vascular
subepithelial ingrowth of
degenerative bulbar
conjunctival tissue over the
limbus onto the cornea
 Shows elastoid
degeneration in the
subepithelial stromal
collagen
 Type I pterygium is most
associated


 Pterygium
 Management:
 Tear substitute

 Advisethe patient to wear sunglasses to
reduce UV exposure and decrease the
growth stimulus

 Pinguecula(sing:
pingueculum)
 Elastoid
degeneration of the
conjunctival collagen
stroma

 Found adjacent to
the limbus

 Band- shaped keratopathy

 Histology shows the deposition of calcium
salts in the Bowman layer, epithelial
basement membrane and anterior stroma

 Cataract has been found to be associated
with the UV band from the sun

 Anterior subcapsular opacities are most
associated, as found by one study

 There is also an increase in the stromal haze

 The epidemiology of UV-induced cataract:
 The ophthalmic community has found it difficult
to accept the cause-effect relationship of UV
exposure in producing cataracts

 Role of UVR in Skin Cancer and Cataracts

 Any relationship b/w the surface ectoderm and
UV exposure

 The National Health and Nutritional
Examination Survey(HANES) and the Model
Reporting Area for Blindness Statistics(MRA)

 Found a strong positive association between UV
rays and the senile cataracts

 Brilliant et al studied 27,785 Nepalese
individuals from the plains, the hills, and the
mountains who were rural village residents
 The no of hours of daily sunlight were determined
for each location.

 They found that persons exposed to 12 h of
sunlight daily were 3.8 times more likely to
develop cataracts than those who were exposed
to only 7 h of daily sunlight

 They also reported a 2.7 times higher
prevalence at altitudes of 185 m and below
than at 1000 m and above

 Similar study conducted by Chatarjee
maintained that the Punjab population who
lived at higher altitudes were less susceptible
to cataract.

 Some other research work made out that
 Cortical
cataracts are in association with UV
exposure

 And as yet no strong positive correlation has
been established by researchers as regards
the
UV exposure and Nuclear Cataracts

 UV and Cataract
 In
summary, the data demonstrate a correlation
between cortical senile cataract and UVB
radiation

 Andtherefore protection against the radiation
may be achieved upon the use of protective
glasses

 Retina
 Ina normal eye, the retina is shielded from much
of the UV radiation by the filtering action of the
cornea and the lens

 Under ambient conditions, the retinal damage is
unlikely

Effects of Ultraviolet radiation in
the retina
Duke Elder states, “On the whole, it is probably
safe to say that the ultraviolet radiations which
might harm the retina do not reach it, and
those radiations of this spectral origin which
DO reach it have not been shown to do
organic or functional harm of any practical
importance to this tissue”

the retina
 When the lens has been removed
 The aphakic eye is subjected to UV radiation in
the range of 320-380 nm, which had previously
been filtered out by the lens.

 Inaddition, the amount of visible radiation also
increases in the aphakes.

 Cystoid
macular oedema(CMO) is one of the
complications that follow cataract surgery.

the retina
 CMO:
 Accumulation of fluid
in the outer
plexiform and the
inner nuclear layers
of the retina with
formation of cyst-like
changes
 These cysts may
later on progress to
give rise to macular
hole

the retina

 Ultraviolet and photosensitisation
 Photosensitisation is the enhanced chemical
reaction to normally harmless
radiation(particularly UVA and visible) that are
induced by the presence of a photosensitiser.

 The patients taking medications belonging to
Quinolone group—Fluroquinolone such as
ciprofloxacin, ofloxacin, etc are to be advised on
UV exposure
 as photosensitisation may occur

Effects of Visible radiation
 Almost all of the radiation is transmitted upto
the retina for processing.

 Not harmful as the structures have evolved to
remain immune to the damage

 However, the long term exposure to visible
spectrum has been found to be associated
with macular degeneration, damage to the
photoreceptors and the pigment epithelium

Effects of Visible radiation

 Solar retinopathy has been found to be
associated with damage from long term
exposure to visible radiation, to the retina

Effects of Infrared radiation
 Wavelengths longer than 3000 nm do not
reach the earth’s surface because
 They are absorbed by water and carbondioxide in
the atmosphere
 Damage from IR radiation covers only from
wavelengths 780 nm to 2000 nm
 Mechanism:
 Thermal damage to tissue leading to
DENATURATION, unlike the UV radiation that
involves photochemical, thermal damage.

 Cornea:
 Opacification, debris, haze, exfoliation
 Burn, necrotic ulceration

 The posterior corneal regions show more damage
than the anterior regions
 Dueto the cooling effect by the tearfilm to minimise
anterior corneal defects
 Also found to raise the aqueus humour
temperature
 Also was seen an increase in the IOP.

 Iris:
 Absorption depends on the pigmentation of the
iris itself
 It has been found that the iris is more sensitive to
the IR

 Pupillary
miosis, aqueous flare and posterior
synechiae

 Congestion, depigmentation, and atrophy

 Iris:

 Inflammation results due to breakdown of blood-
aqueous barrier, which allows leakage of the
proteins in the AC and thus the AC flare.

 Lens:
 Themorphology of cataracts caused is poorly
understood.

 Posterior
cortical opacity is in strong relation to
the IR exposure

 Lens:
 Verhoeff and Bell suggested that the outer
surface of the cornea was air-cooled and that the
anterior capsule of the lens was cooled by the
circulation of the aqueous humour
 Thus,cataract formed on the posterior surface of the
lens because of its elevated temperature

 They further postulate that heat interferes with the
function of the ciliary body which subsequently
interferes with the metabolism of the lens

 Lens:
 In
acute IR-induced cataracts, anterior
subcapsular opacity is common

 However, posterior subcapsular opacity is a
delayed process of the anterior damage migrating
posteriorly

 As is already known that the damage occurs
via thermal mechanism
 Heatingof the tissue above its normal
temperature has been linked to an increase in the
metabolism of the affected tissue

 Therefore, the metabolic acceleration could lead
to
 Prematureaging as a result of an abnormal
accumulation of metabolic by-products

 However, osmotic involvement has also
been suggested in the development of
senile cataracts, invoking
 an accumulation of water-soluble
substances as the means of loss of
lenticular transparency

 Retina:
 Damage due to the indirect thermal injury to the
neural elements of the retina secondary to IR
absorption by the RPE.

 Injuryoccurs in durations ranging from
microseconds to several hours

 Retina:
 Two mechanisms have been proposed.
 Thermal mechanism(long wavelength)
 Due to the elevation of temperature of the irradiated
tissue,eg Necrotic burn

 Photochemical mechanism(short wavelength)
 Due to phototoxicity

Effect of Radiation
 Choroidal melanoma, iris tumours
,retinoblastoma have been linked to radiation,
or mutation induced due to radiation that may
pass onto new generations.

Glare
 Is defined as

“that condition of vision in which there is discomfort
or a reduction in the ability to see significant
objects, due to an unsuitable distribution or range
of luminances or to extreme contrasts in space”

Glare
 is a catch-all term that usually includes three
separate effects:
 Disability
glare
 Discomfort glare

 Light adaptation glare

 Specular reflection glare, previously thought to
be glare when, in fact, it is not glare according
to the current definition of glare

Glare
 Disability glare
 Due to stray light falling on the retina

 Due to scatter from the media opacities
 Which may include cataract, corneal dystrophy,
translucent iris, iritis albinism, vitreous opacities

Glare
 As shown in the previous picture, light that should
have contributed to the brightness of the retinal
image is instead scattered to adjacent parts of the
retina

 This lowers the brightness of the retinal image
and increases the brightness of the background,
lowering contrast

Glare
 Some calculation…
 Assume a simple target with a luminance of 100
cd/m2 on a background with a luminance of 25
cd/m2.
 Then this target would have a contrast of

 And if disability glare adds a veiling luminance of 10 cd/m2
then

Glare
 Itis the most commonly used clinical measure of
glare

Glare
 Discomfort glare
 Illuminationin part of the visual field is much
greater than the level of illumination to which the
eye is adapted

 Itis a sensation of irritation and pain from sources
of light in the field of view

Glare
 Unlikedisability glare, the cause of which is
mostly understood, the physiologic basis of
discomfort glare is unknown

 Because so little is known about the origin and
measurement of discomfort glare, there is little
international agreement on how it should be
specified

Glare
 The most common measure of discomfort glare is
the border between comfort and discomfort(BCD)

 As an example, a person may be shown a range
of lights of varying brightness and asked to
evaluate each in terms of its discomfort by placing
it on the following semantic scale

Glare

 It is unnoticeable
 It is just noticeably uncomfortable

 It is uncomfortable

 It is very uncomfortable

 It is intolerable

Glare
 Headache is one of the so many effects of glare

 Nasociliary nerve- driven pathway is involved

 Therapid fluctuations in the pupillary diameter
would accompany continuous innervation to the
CNIII and this causes a continuous relay offerent
signals from the iris-ciliary body complex via the
nasociliary division.

Glare
 Light adaptation glare
 Is the reduction in vision caused by the after
image of a glare source producing a central
positive scotoma after directly looking at a bright
light

 Lightadaptation glare can persist even when the
source has already been removed from the
observer’s sight unlike disability glare

 Forms the basis of Macular Function
Test>Photostress Test

Glare
 Light adaptation glare
 Since this glare is due to light adaptation of the
photoreceptors

 Ithas a negative impact on patients with macular
problems

Glare
 Specular reflection glare
 AkaVeiling Reflection
 When patches of bright light are reflected by
smooth, shiny surfaces
 Then there occurs a reduction in the quality of vision
via the reduction in the contrast
 Control:
use of polaroid lenses

References:
 Donald G Pitts, Robert N Kleinstein,
Environmental Vision, Interactions of the Eye,
Vision, and the Environment;Alan L Lewis,OD,
PhD, Chapter Five:Basic Concepts in
Environmental Lightning;Donald G Pitts, OD,
PhD, Chapter Six: Ocular Effects of Radiant
Energy

 William J Benjamin, Borish’s Clinical
Refraction;David B Elliott, Contrast Sensitivity
and Glare Testing

References:
 Jack J Kanski, Brad Bowling, Clinical
Ophthalmology A Systematic Approach
 Troy E Fannin, Theodre Grosvenor, Clinical
Optics;Chapter Seven:Absorptive Lenses and
Lens Coatings
 http://en.wikipedia.org/wiki/Glare_%28vision%2
9

 http://www.allaboutvision.com/sunglasses/spf.ht
m

References:
 http://sdhawan.com/ophthalmology/lens&catara
ct.pdf
 www.nei.nih.gov

Effects of radiation and glare on human eyes

Effects of radiation and glare on human eyes

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