The sun is the most abundant source of optical radiation for the child's eye. ¹

The Sun emits a wide spectrum of electromagnetic radiation. Optical radiation, the portion capable of penetrating the ozone and reaching the Earth's surface, is composed of ultraviolet radiation (9%), visible radiation (50%) and infrared radiation (40%).

In the ultraviolet (UV) spectrum only UVB (280-320 nm) and UVA (320-400 nm) reach the Earth's surface, predominating UVA (95%) over UVB (5%). UVC does not exist in nature, being produced only by man (eg, welding arc).².

Ambient exposure of the eyes to UV rays is complex. It depends on the solar angle, the weather conditions and the reflectivity of the surfaces.

The content of UV radiation varies according to the time of day, geographical location and reflectivity of the environment.

Reflectivity is extremely high on snow (94-80%), lower on the open sea (20%), sand (10%) and grass (9%). At ground level the value is 1%.

The proximity of the equator and higher altitude are other factors that increase the reflectivity of the solar rays.². Due to their physical characteristics, these rays do not participate in the visible light spectrum, but may be responsible for the ocular disease.

On the skin, UV radiation can cause tanning (UV-A), burning or even predisposes to neoplasia when repeated exposure occurs (UV-B). In the eyes can cause acute pathology (photokeratitis, photoretinitis) or predispose to degenerative pathology. 

It has been considered that solar radiation, both in and outside of the UV range, contributes to the development of ocular aging-related pathologies such as cataracts and degenerative retinal disease. This occurs mostly in the adult or elderly. 

Solar radiation is also responsible for the development of degenerative conditions of the conjunctiva and cornea. The eyes are naturally protected from UV radiation and receive only a small fraction of UV from the environment under normal circumstances Several structures contribute to this effect.

Both the supraciliar bone arcade and the eyelids reduce the radiation input, while eyelid closure and pupil diameter variation are additional protective mechanisms.³. The structures of the anterior segment absorb a portion of UV radiation.

The retina is largely protected from UV rays by the anterior segment. The conjunctiva and cornea block the transmission of radiation under 300nm.

The adult lens blocks radiation between 300 and 400 nm. This effect begins at age 20 and increases linearly for the following 30 years.

In children and young adults, because of the different protein content of the lens, there appears to be a narrow-band window in which UV rays around 320-330 nm penetrate and reach the retina.

Its clinical impact is unknown, although experimentally this increased susceptibility has been associated with the presence of lipofuscin, which content increases proportionally in the retina along the first 2 decades of life ^{1, 2}.

 

How to protect children's eyes from the Sun?

Avoid direct exposure to the sun when the environmental radiation is at its highest, such as between 11 am and 3 pm on summer days, or at places where reflectivity is high.

Another measure should include providing a good shade on the face, such as a wide-brimmed hat or cap, wearing sunglasses (when reflectivity is high) and protecting the periorbital skin.

Instruct the children about the care they should have, especially in the case of a solar eclipse.

 

In what situations is the use of sunglasses obligatory?

When exposed to high levels of UV radiation, such as at snow, ice and high altitudes (on the mountain).

When the child has an ocular disease, such as aphakia, aniridia, albinism or other retinal conditions (pigmentary retinitis, maculopathy) or takes photosensitizing medication.

- The use of a wide-brimmed hat or cap is effective, protecting the child’s face and eyes from the sun, while allowing the child to understand the hostility of the environment by having the correct notion of brightness. It also protects the face from radiation.

- Dark lenses make the perception of the environment darker. When the gait is not fully developed they can interfere with the perception of space and navigation.

- The combined use of hat and glasses has additive protective value. 

- Under circumstances of high UV index, sun exposure should be avoided.

 

How should the glasses be like?

It is important to inform parents that glasses with dark lenses are not synonymous with ocular protection, and that lenses should be of high quality and the frame should be protective.

As a whole, frames and lenses must conform to EN ISO 12312-2: 2015 which is certified by the manufacturer with the CE mark, meaning that it has complied with the standards. ⁵.

 

Lens quality:

The lenses must have a UV filter close to 100%, regardless of their color.

They must have good optical quality (no distortion) and should never be scratched or have any crack.

They should transmit only visible radiation and block all UV radiation in any direction.

For children with photophobia less intense color filters may be more suitable.

 

Shape and contour:

The frame must protect from direct and reflected radiation as much as possible.

It must cover the orbit in order to prevent sunrays from entering from all the directions, wich means from the front, above, below and the sides (a good example are snow or pool goggles).

The outline of the glasses should always be in contact with the skin, both forward and sideways.

If necessary an elastic band might facilitate positioning.

 

Other recommendations:

- The use of a wide-brimmed hat or cap is effective, protecting the child’s face and eyes from the sun, while allowing the child to understand the hostility of the environment by having the correct notion of brightness. It also protects the face from radiation.

- Dark lenses make the perception of the environment darker. When the gait is not fully developed they can interfere with the perception of space and navigation.

- The combined use of hat and glasses has additive protective value. 

- Under circumstances of high UV index sun exposure should be avoided.