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 RetinaResults into GLARE

Radiation

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Electromagnetic Spectrum

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FG Figure 7-2

ULTRA-

VIOLET

RADIATION

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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.”


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

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


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

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.


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.


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: The morphology 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 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


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.

Injury occurs 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

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

http://en.wikipedia.org/wiki/Glare_(vision)

http://en.wikipedia.org/wiki/Glare_(vision)





References:

http://sdhawan.com/ophthalmology/lens&cataract.pdf

www.nei.nih.gov



http://www.nei.nih.gov/

Thank You

Education

Effects of radiation and glare on human eyes