NORMAL PROTECTION

The human eyes are protected by several factors to limit the exposure. The normal horizontal gaze decreases the exposure to UV rays entering the atmosphere. The brows, nose and cheeks also act as barriers against UVR. The eyelids protect the eye when one squints against the bright sunlight and thus reduces the exposure to UVR. The lateral part of the eye is well protected but the part of the eye next to the nose is more at risk and this is where diseases develop because of exposure to ultra-violet irradiation.


PROTECTION AGAINST UV IRRADIATION

A hat with a peak will eliminate a large percentage of UV irradiation. Protective sunglasses are beneficial to filter the UV rays, which enters the eye. Many of the tissues of the human eye absorb UV rays and prevent the dangerous rays from damaging the retina, (the equivalent of the film of a camera in the human eye).


HOW UV IRRADIATION EFFECTS THE EYES

A
CORNEA

The cornea is the transparent layer, which forms a front surface of the eye.

1.
Photokeratitis 

Photokeratitis is caused by UVB and UVC rays. Most commonly this condition is known as "arc eyes" when the eyes are exposed to welding and flames. Snow blindness is also an example of damage of the supervisual layers of the cornea by over exposure to ultra-violet light. These conditions are usually self-healing within eight to twelve hours if the exposure is not excessive.

2.
Pterigia

This is an over growth of blood vessels and fibrous tissues from the white part of the eye.It grows from the white of the eye closest to the nose towards the pupil, which is the black center in the coloured part of the eye.It usually causes scratchiness and irritation and if it reaches the central part of the cornea (pupil), an operation is necessary to remove the pterigium to prevent permanent damage to vision.

3.
Pingueculum

This condition is a degenerative condition of the conjunctiva (the lubricated surface of the eye) in a reaction to exposure to ultra-violet light.

4.
Climatic droplet keratopathy

In this condition the surface of the cornea becomes irregular with chronic irritation and reduction in vision


B
LENS

Epidemiological and clinical observations increasingly support the relationship of exposure to UVB rays and the formation of cataracts. These studies where performed amongst the Australian aborigines as well as in China, Nepal, Tibet and India where there is a high exposure to ultra-violet light.


C
MAKULA

The macula is the central yellow spot of the retina, and enables the eye to see small objects. Studies point to a relationship between macular degeneration and UVR exposure.


SUNGLASSES AND YOUR LIFESTYLE

Because of the changing life styles with people spending more time outdoors as well as the deficient ozone layer over Southern Africa, the protection against UVR is becoming increasingly important. The incidence of skin cancer directly linked to UV exposure is well documented and is increasing. The use of sun block and a sun hat as well as avoiding exposure during peak times between 10am and 2pm are measures to prevent damage because of ultra-violet irradiation. The eyes also need special protection and sunglasses are readily available to enable everybody to afford a certain degree of protection against UV irradiation.

The ideal situation would be to have complete protection with lenses in sunglasses absorbing a 100% UV rays below 400 nm. Cosmetic sunglasses should eliminate the UVB range of the most dangerous rays and at least 70% of the UVB range.

Sunglasses can be devided in three categories:

Cosmetic sunglasses, 
which can also be described as "fun" glasses. 
General purpose sunglasses:
These are the well-known brand names that can be bought without a prescription. 
Special purpose sunglasses, which is prescribed and made up to certain specifications. 
At the moment there is no specific standard for sunglass lenses in South Africa but the three different groups should at least give the following protection:

Cosmetic sunglasses – 70% UVB elimination 
General purpose sunglasses – 90% UVB elimination 
Special purpose sunglasses – 99% UVB elimination 


WHO SHOULD RECEIVE UV PROTECTION?

The use of sunglasses in children below the age of eight years is controversial. The exposure to ultra-violet light leads to the development of cells in the lens, which is called chromophores. These cells contain pigment, which absorbs the UV rays, which enters the lens and protects the sensitive retina against damage. If these cells do not develop within the first eight years of age, the eye is at risk later in life. It is important then that children should not wear sunglasses in the first eight years of age to enable the eye to build up its natural protection against UV irradiation. After the age of eight years sunglasses is recommended for anybody who spend long periods of time outdoors.


The use of sunglasses with special protection is recommended for: 

People who are frequently in areas high in UV irradiation: snow skiing, sunbathing and mountain climbing. 
People with pinguecula, pterigia and macula degeneration. 
People who spend excessive hours in the sun. 
Workers in vocations rich in UV irradiation, welders, chronic workers, graphic art workers and researchers.