Oftalmologia Pediátrica e Estrabismo


Sunglasses for children
The need or advice of sunglasses for children is a recurrent subject of public debate, and its real importance is many times amplified, especially when summer approaches.
Any aggression of the environment has a greater repercussion in children, because they are in stage of development, and therefore all prevention aspects are very important.
Paediatric ophthalmologists are many times enquired about this subject: Must children wear sunglasses? Should children wear sunglasses? Can children wear sunglasses? These are three distinct questions that deserve various comments.

These issues concern contemporary society for three types of reasons:

(1) There is today a collective consciousness of climatic and atmospheric alterations that tend to reduce natural protections;

(2) There is now a critical consciousness of the importance of preventive medicine concerning the aggressions of the environment; and finally,

(3) In the globalized world, a “marketing” dynamic was developed, often unapparent, targeting consumption: today, there are shops specialized in sunglasses sale, and this fact reflects the importance of this market niche; there is no clothing or perfume trademark that has not its own prototype of sunglasses; television and newspapers daily “invade” our homes with images of stars, from all areas of society, having in common a clothing and frequently sunwear (not always correctly used) trademark.

Solar radiation

First, it is necessary to know the reasons for eye protection.

Sunlight or solar radiation is composed of several components, among which ultraviolet radiation (UV) situated in the electromagnetic spectrum beyond visible light, at its violet end. These UV rays are the most harmful for the visual system, in case of exposure. According to wavelength, decreasingly, UV can be subdivided in UV-A, UV-B and UV-C.

The importance of the ozone layer and the alterations it suffers are at present very relevant subjects. The ozone is just a special form of oxygen, formed from normal oxygen when it is present above a certain concentration in the upper atmosphere. In these conditions, by photochemical reaction with UVC radiation, a very thin layer of about 2 – 3 millimetres of this gas is formed in the stratosphere (at about 50 km of altitude) and is more or less homogeneously distributed by the stratospheric winds. Curiously, the main function of this ozone layer is to filter out the UV rays of solar radiation (and also to stabilize the concentration of oxygen in the atmosphere).

Effects of solar radiation on the visual system

The noxious effects of UV radiations are the real problem of exposure to sunlight. They depend not only on the intensity of the radiation, indicated by the UV radiation index (World Meteorological Organization and UN environmental programme), but also on the time of exposure.

Which are the ocular lesions due to UV radiation?
It is necessary to distinguish immediate (acute) lesions caused by radiations from medium-term and long-term ones.

From the acute, it is important to refer to palpebral burns, often not valued within ophthalmological lesions. It is essential to stress the importance of the eyelids in visual function, and also to remember that the skin of the eyelids presents the risk of developing a tumorous pathology during lifetime, if overexposed.

Among acute lesions, the sunburn of the cornea – photokeratitis – is probably the most serious. The symptoms are pain, which may be intense especially in the presence of light, and a temporary decrease of visual acuity. This type of lesion depends on the wavelength (the shorter the wavelength, the more frequent and more serious the lesion) and on the intensity of the radiation. A small amount of short wavelength radiation, such as UVC, can cause lesions, but fortunately this type of radiation hardly reaches the surface of the Earth. In Portugal, the majority of these lesions are caused by industrial appliances, such as welding devices. Nevertheless, this type of lesion is described in situations of prolonged exposure to UVB, as for example after activities on the snow, especially recent snow that reflects about 85% of the radiation.

I had the opportunity of studying the causes of emergency in paediatric ophthalmology, during the years 2005 and 2006, in Hospital São João in Porto, where all paediatric emergencies from this municipality are received, and which functions as reference hospital, in this medical specialty, for all the north region of Portugal. During that period, in a total of 4 692 patients, we did not examine any case of sunburn of the cornea in children for overexposure.

The major lesions due to the long-term effects of radiations are:

(1) Alterations of the transparency of the crystalline lens, which can cause cataract: they are a consequence not only of UVB but also of UVA action;

(2) Age-related macular degeneration: a disease that affects the central part of the retina and that can lead to blindness; developed usually in a late stage of life, around 70 years of age, it may be related to the toxicity of light.

In these cases, there is a cumulative effect of the radiations throughout life.

The purpose of sunglasses

First of all, it is necessary to know the functions of sunglasses. Most people wear them to improve visual comfort in the presence of sunlight. This is a very important benefit, but the main purpose of sunglasses should be to protect children’s eyes from harmful radiations: they should filter out 100% of the ultraviolet radiations (UVA, UVB and UVC) and, if possible, the blue segment of visible light.

Children spend more time exposed to sunlight than adults. It was estimated that the average of radiation received by children is the triple of the adults, and that about 80% of the radiation is received before the age of 20 years.

Besides, the child’s crystalline lens transmits more short wavelength visible radiation (blue) and ultraviolet radiation to the retina than the adult’s. It was estimated that 75% of the radiation reaching the retina is received before the age of 10 years and only 10% after the age of 25 years.

These data help to understand that protection, if necessary, is more important during the periods of life in which children are more exposed to solar radiation.

Furthermore, the exposure to harmful radiations depends on the UV radiation index. Children must be protected especially when this index rises above 10 (in a range from 0 to 15). In Portugal, these values are rarely reached. Protection is also very important in environments of great exposure, which depend on geographic factors (more radiation in regions near the equator), in places at high altitudes (mountain) and in zones of intense reflection of light, such as areas covered with snow and large water surfaces.

Since when can children wear sunglasses?

Children can wear sunglasses at any age. But a good rule is to wear them only since the moment they can handle them autonomously.

Protection from solar radiation is important since the age the child changes its lifestyle, begins to have activities outdoors and is more exposed.

Eye protection with sun lenses is important, especially:

- On days with high UV index;

- During the periods of the day in which radiation is more intense (from 10 a.m. to 3 p.m.);

- In places of greater exposure: high altitudes (mountain) and very reflecting surfaces (snow and water).

Criteria to choose sunglasses for children

The most important criterion is quality, not always compatible with fashion trends.

Parents should ascertain several characteristics in sun lenses:

1. The lenses must filter out 99 – 100% of the radiation with wavelengths below
400 nm (all UV radiation). If possible, they should also filter out the radiation between 400 nm and 500 nm (blue light).

2. The lenses must have good optical quality, to avoid the distortion of images.

3. The tint of the lenses should provide visual comfort in the presence of sunlight, but it should not be too dark, in order to respect the natural colours of objects and/or to preserve visual acuity. The intensity of the tint and the lens capacity to filter out harmful radiation cannot be confused.
The tint intensity ranges from 0 to 4. For sunlight conditions in Portugal, the best option is a 2 – 3 tint. Only in special situations should darker lenses be used.
The lenses should preferably be tinted grey or brown (amber).

4. The frame and the lenses should be resistant to impact. Children are more subject to traumatisms, and therefore it is necessary to avoid lenses and/or frame breaking risks. The glasses should not have sharp edges or protrusions capable of injuring eye structures.

5. The structure of the glasses should protect both the eyes and the eyelids: the frame should perfectly fit the face and should be sized to prevent reflected light from reaching the eyes.

When acquiring sunglasses, parents should check the presence of the CE symbol and the inscription of the standard the product conforms to.
In Europe (and in Portugal), there is a special standard (EN – 1836 of 1997) that requires the following: identification of the manufacturer, filter rating, driving adequacy.

The manufacture and trade of sun lenses are covered by the legislation that regulates the equipments for individual protection (EIP) (Directive 89/686/EEC of the Counsel, of 21 December 1989).

Sunglasses are not the exclusive means of eye protection!

Sun lenses help to protect the visual system from solar radiation, especially on days and in situations implying greater exposure. Anyway, it is important to remind:

1. The best protection is to avoid solar radiation. Exposure should be avoided on very sunny days and at hours of more intense sunlight (from 10 a.m. to 3 p.m.);

2. A brimmed hat or a cap reduce in about 50% the amount of direct light that reaches the eyeball, and so they can be excellent means of protection.

Aesthetic motivations and parallel market
Many times sunglasses are acquired mainly for aesthetic reasons.
And it is common knowledge that they are often bought in unspecialized shops with trendy offer and low prices. This type of market is proliferating almost everywhere, because supervision is not efficient enough. It was estimated that about 30% of sunglasses sold every year are illegal, and therefore not subject to the quality control imposed by European legislation.

But today, in Portugal, parents are increasingly concerned with their children’s health, including preventive care. Thus, less and less sunglasses of bad quality are bought.

Are quality sunglasses always expensive?

Not necessarily. Sunglasses have not to be expensive to offer a good protection against UV radiation. In most cases, their high price is due to marketing criteria of the trademark. There is no need to buy frames or lenses with the logotype of known trademarks.
The important is to check the efficacy of the lenses in filtering out all UV rays and about 75 – 90% of visible light, in order to provide eye comfort.
But a low price should never deter parents from avoiding lenses without these specifications or not certified.

How to check the optical quality of sun lenses

A correct vision with sunglasses depends essentially on two factors: the optical quality and the tint of the lenses.

One of the requirements for quality sunglasses is the good optical quality of the lenses. Sun lenses of bad optical quality alter vision and can cause eyestrain and headaches.
When sun lenses are bought in specialized points of sale, their optical quality is in principle ensured. Nevertheless, a short exam and a simple test can help you to verify it: observe closely both lenses, to check that they are equally uniform in appearance, including tint; approach each lens to a line or an object, and move the lens in several directions, to confirm that there are no distortions of the image.

About the tint, it is important to stress that its intensity is not related to the lens capacity to filter out UV radiation. In fact, clear lenses also protect the eyes from UV! Besides, very dark lenses can reduce visual acuity, alter the real colours of objects and cause eyestrain.

It is common knowledge that the eyes have special mechanisms of defence. In case of exposure to intense light, the eyelids close, the eyes deviate from the source of light and even the head is positioned in order to avoid it.
But the reaction of the pupil is the most known factor of protection. The pupil is the central round dark area, limited by the iris, through which the light enters the eye. The pupil closes reflexively with light, reducing substantially the amount of light that enters the eye. In normal conditions, children are less affected by glare, because this pupillary reflex is more active and reduces more the pupil area than in adults.
Although not proved, it is possible that an excessive use of sunglasses diminishes pupillary reflexes.
But the risks of wearing sunglasses are due to the use of bad quality sun lenses: if the dark lenses do not filter out the UV rays, they reduce the reflex of the pupil and allow a greater quantity of these radiations to enter the eye.
There are also risks related to traumatisms. Children are more subject to trauma, and if the lenses and the frames are not resistant, the risk of lesion is increased.

Special situations requiring special protection
Children submitted to cataract surgery need special protection care, because without the crystalline lens the amount of radiation that passes to the retina is increased.

Some treatments increase the sensitivity of ocular tissues to UV radiation. These include a few antibiotics, such as sulphonamides and tetracyclines, treatments for psoriasis and vitiligo, and a few antidepressant and anti-epileptic drugs.

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