EFFECTS OF RADIATION AND GLARE ON EYE Amrit Pokharel B Opt0metry, III rd year
Jan 20, 2015
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 RetinaResults into GLARE
Radiation
04/10/20238
Electromagnetic Spectrum
04/10/20239
Electromagnetic Spectrum
FG Figure 7-2
ULTRA-
VIOLET
RADIATION
04/10/202310
Electromagnetic Spectrum
FG Figure 7-2
ULTRA-
VIOLET
RADIATION
INFRARED RADIATION
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
Ionizing Radiation
alpha particle
beta particle
Radioactive Atom
X-ray
gamma ray
Ionizing Radiation
Paper Wood ConcreteAlpha
Beta
Gamma
Energy
Low
Medium
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.”
Non ionizing Radiation
The radiation energy is lower than the binding energy of the electron
Only states change Ground ---excited
Non ionizing Radiation
The change to the irradiated is brought about as: Thermal Effect
Photochemical Effect
Photoluminescence(fluorescence)
Non ionizing Radiation
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
Non ionizing Radiation
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
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
It cuts 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): As the property of fluorescence in inherent
to the lens, the lens is capable of absorbing UV rays
This absorption gives off the formation of material-fluoregens, that give the characterstic colouration(yellowish) to the lens.
Concentration of the radiant energy by the eye
Spectrum…
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
Absorption of the spectrum
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
Absorption of the spectrum
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
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation Pterygium
Management:Tear substitute
Advise the 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
Effects of Ultraviolet radiation Band- shaped keratopathy
Histology shows the deposition of calcium salts in the Bowman layer, epithelial basement membrane and anterior stroma
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation 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.
Effects of Ultraviolet radiation 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
Effects of Ultraviolet radiation UV and Cataract
In summary, the data demonstrate a correlation between cortical senile cataract and UVB radiation
And therefore protection against the radiation may be achieved upon the use of protective glasses
Effects of Ultraviolet radiation Retina
In a 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”
Effects of Ultraviolet radiation in 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.
In addition, the amount of visible radiation also increases in the aphakes.
Cystoid macular oedema(CMO) is one of the complications that follow cataract surgery.
Effects of Ultraviolet radiation in 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
Effects of Ultraviolet radiation in the retina
Effects of Ultraviolet radiation 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.
Effects of Infrared radiation
Cornea: Opacification, debris, haze, exfoliation Burn, necrotic ulceration The posterior corneal regions show more
damage than the anterior regions Due to 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.
Effects of Infrared radiation
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
Effects of Infrared radiation
Iris:
Inflammation results due to breakdown of blood-aqueous barrier, which allows leakage of the proteins in the AC and thus the AC flare.
Effects of Infrared radiation
Lens: The morphology of cataracts caused is
poorly understood.
Posterior cortical opacity is in strong relation to the IR exposure
Effects of Infrared radiation
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
Effects of Infrared radiation
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
Effects of Infrared radiation
Effects of Infrared radiation
As is already known that the damage occurs via thermal mechanism Heating of 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 Premature aging as a result of an abnormal
accumulation of metabolic by-products
Effects of Infrared radiation
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
Effects of Infrared radiation
Retina: Damage due to the indirect thermal injury
to the neural elements of the retina secondary to IR absorption by the RPE.
Injury occurs in durations ranging from microseconds to several hours
Effects of Infrared radiation
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
Effect of Radiation
Effect of Radiation
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
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
Glare
Disability 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
Disability glare It is the most commonly used clinical
measure of glare
Glare
Discomfort glare Illumination in part of the visual field is
much greater than the level of illumination to which the eye is adapted
It is a sensation of irritation and pain from sources of light in the field of view
Glare
Discomfort glare Unlike disability 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
Discomfort 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
Discomfort glare
It is unnoticeable It is just noticeably uncomfortable It is uncomfortable It is very uncomfortable It is intolerable
Glare
Discomfort glare Headache is one of the so many effects of
glare
Nasociliary nerve- driven pathway is involved
The rapid 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
Light adaptation 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
It has a negative impact on patients with macular problems
Glare
Specular reflection glare Aka Veiling 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%29
http://www.allaboutvision.com/sunglasses/spf.htm
http://www.cancer.org/Research/CancerFactsFigures/index
References:
http://sdhawan.com/ophthalmology/lens&cataract.pdf
www.nei.nih.gov
Thank You