The first signs are easily overlooked: the son couldn't copy everything down from the blackboard because «the teacher's handwriting was so small». The daughter couldn't make out the sign because «we drove past it too quickly».
But then the child keeps sitting too close to the television, blinks a lot and seems to be squinting all the time. By now, at the very latest, it's time to see an optician, as the child might be short-sighted: they can see clearly up close, but objects far away appear blurred.
Increased risk of blindness
The number of short-sighted children worldwide has been rising significantly for decades. A Chinese research team describes this as a global health problem: the scientists analysed data on 5- to 19-year-olds from 50 countries. According to their findings, 20 years ago one in four children was short-sighted; now it is one in three. Experts predict that this trend will continue to rise, and by 2050, one in two children could need glasses.
It is advisable to keep your prescription below minus three dioptres; above this, the risk of complications increases significantly.
Anja Palmowski-Wolfe, ophthalmologist
You might think it's no big deal – after all, there are worse things than having to wear glasses. However, short-sightedness – the technical term is myopia – increases the risk of numerous eye conditions, some of which can lead to blindness. These include retinal detachment, macular degeneration, increased intraocular pressure (glaucoma) and clouding of the lens, known as cataracts.
«There is a difference between developing a clouded lens at the age of 70 or 80 and developing it as early as 40 or 50,» says Anja Palmowski-Wolfe, Senior Consultant at the Eye Clinic of the University Hospital of Basel. In principle, therefore, the theoretical aim is that nobody should become short-sighted. «That is, of course, utopian, so we at least try to stay below minus three dioptres, as the risk of secondary conditions increases significantly above that level.»
The influence of daylight
A key factor in preventing short-sightedness from developing in the first place is light, particularly daylight. Various studies have shown that it affects the length of the eye – an eyeball that is too long leads to short-sightedness. «Making a change here would go a long way towards ensuring we have fewer short-sighted children,» says Palmowski-Wolfe.
Many classrooms suffer from poor lighting conditions, with illuminance levels of around 150 lux. According to Palmowski-Wolfe, studies have shown that increasing the brightness to levels of around 500 lux leads to a reduction in the incidence of new cases of short-sightedness in children aged between 6 and 14 within just one year.
This could be achieved with special daylight lamps, light-coloured walls and furniture, and good «window hygiene» – large, clean windows with no trees or blinds blocking the light. «Sufficient brightness in the classroom is indeed one of the most effective measures against myopia,» says Hakan Kaymak of the Makula-Retina-Myopia Centre in Düsseldorf, which is the first research centre in Germany to focus specifically on the prevention and treatment of short-sightedness. «I would very much like to see 1,000 lux become the standard in classrooms.»
Science tells us that children should spend at least two hours a day outdoors, where the light level is at least 1,000 to 3,000 lux, even on rainy days. Even in the shade or when wearing sunglasses, you still get significantly more light than indoors. «This effect is very strong,» says Kaymak. «We know, for example, that children whose parents are both short-sighted have a 60 per cent chance of becoming short-sighted themselves. However, this risk can be halved by spending two hours a day outdoors.»
A multifactorial process
Although the observational data are very clear and intervention studies also show that spending more time outdoors can reduce the risk of children developing short-sightedness, experts do not yet know exactly why light protects against short-sightedness. There are, however, a number of hypotheses. «It is very likely a multifactorial process,» says Leila Eppenberger, who treats and researches myopia in children and adolescents at the Inselspital in Bern.
«We now know that the intensity of light influences various biological signalling pathways that regulate the longitudinal growth of the eye.» Bright light, for example, appears to promote the production of dopamine in the eye. It is thought that this neurotransmitter, in turn, may prevent the eye from growing too long. In addition, the light spectrum, contrast sensitivity and the visual environment are also thought to play a role.
After reading for 20 minutes, you should take a break and look into the distance for a while.
Hakan Kaymak, ophthalmologist
A recent study by the SUNY College of Optometry at the State University of New York concludes that it is not only light that has an effect, but also the close-up work commonly carried out indoors. Focusing on nearby objects for long periods in poorly lit rooms means that less light reaches the retina – with the well-known consequences for dopamine levels.
Furthermore, the eye's accommodation itself has an influence on the development of short-sightedness – that is, the constant contraction that occurs during close-up work. «It makes no difference to the eye whether you're looking at a mobile phone, a laptop or a book,» says Kaymak, «the important thing is to maintain a sufficient distance – around 30 centimetres – whilst reading and to take a break every 20 to 25 minutes to look into the distance for a while.»
Special eye drops
To minimise the progression of existing short-sightedness, Palmowski-Wolfe recommends glasses with what is known as peripheral defocus. In an elongated, short-sighted eye, standard single-vision glasses produce a sharp image on the central retina; in the periphery, however, the focal point lies beyond the retina.
«These special lenses now have segments in the peripheral area that project a sharp image onto specific points on the peripheral retina, thereby slowing the growth of the eye,» explains Palmowski-Wolfe.
Health insurance funds do not yet routinely cover the cost of these glasses – around 350 francs per lens. However, they do cover the cost for children with an above-average axial length who, without intervention, are expected to develop short-sightedness of more than minus five dioptres.
According to studies, these glasses can reduce the progression of myopia by one dioptre over three years. «If such glasses or contact lenses based on this principle are not an option or do not produce the desired effect, treatment with low-dose atropine eye drops can also be used,» says Palmowski-Wolfe.
Night-time contact lenses cause the cornea to change shape
The medicine has been tried and tested for decades and, particularly at low doses, has hardly any side effects. «You have to use it every evening until the age of 15 or 16,» says Düsseldorf-based ophthalmologist Kaymak, «and we've had good results with it.» However, the first choice for treating myopia in children is spectacles with defocusing lenses. The child should be monitored after six and twelve months to see whether the eye is growing normally again. «If the treatment goal is not achieved with the spectacles, 0.05 per cent atropine can be administered as a supplementary treatment,» says Kaymak.
Another option is what are known as night lenses. These contact lenses are worn overnight. They reshape the cornea in such a way that the refractive power changes, meaning you do not need glasses during the day. «It's almost a cosmetic product, with the added benefit that it slows the progression of myopia because it reshapes the cornea,» says Kaymak. The downside is that poor hygiene can lead to eye infections. Furthermore, the cornea reverts to its original shape over the course of the day, meaning your vision is worse in the evening than it is in the morning.
Acting with foresight
The crucial phase in the development of short-sightedness is roughly between the ages of 8 and 16. Palmowski-Wolfe advises that it is certainly worth visiting an optician earlier than that: «When parents bring their three- or four-year-old children in, we can assess where the child stands and lay the groundwork for assessments two or three years down the line.» There are ophthalmologists who specialise in children, and if short-sightedness has indeed developed, practices specialising in myopia are a good place to turn to.
«It is important that the ophthalmologist takes two measurements and regularly checks the axial length and refractive power over the years, without the influence of accommodation,» says Palmowski-Wolfe. In children, these measurements should be taken whilst the eyes are in a state of cycloplegia. This involves using eye drops to relax the eyes, preventing any accommodation from taking place that might distort the measurement results. This is important because an inaccurate assessment of visual acuity can lead to an unsuitable prescription for spectacles.
Most children have normal vision until the end of nursery school. As short-sightedness often only develops once children start school, experts also refer to it as «school myopia».
Prevention in families and schools
Such an examination is also important because not all cases of myopia are the same. «There is, for example, a form of short-sightedness that is not caused by the length of the eye,» says Bern-based ophthalmologist Eppenberger. In such cases, conventional treatments would only be of limited effectiveness. Furthermore, it is necessary to assess on an individual basis at what stage of myopia progression a child currently is: «This personal risk profile is decisive in determining which measures should be taken – and to what extent – to prevent the progression of short-sightedness,» says Eppenberger.
Above all, she recommends prevention, which can take place both at home and at school. Children who spend plenty of time being active outdoors and avoid prolonged close-up work without taking breaks have a good chance of keeping their eyes healthy. «A good approach to this is the 20:20:2 rule: after 20 minutes of reading or close-up work, you should look into the distance for 20 seconds and spend two hours outdoors in daylight – everyone benefits from this.»
