What are they?
Refractive errors are optical defects that appear when the eye is unable to focus the image in the retina. There are basically three types:
- Hypermetropia (long-sightedness): The eye is short or has little focussing power, insomuch as the image is focussed behind the retina meaning that the patient's vision is blurred at close range. In mild and average hypermetropia, the child can make an accommodation effort and make focus in the retina possible, thereby obtaining good vision. However, a prolonged effort may cause tiredenss, headache and eye discomfort.
- Myopia (short-sightedness): Rays of light focus in front of the retina because the eye is long or the focussing power is excessive, meaning that distant objects are blurred to the patient. In this case, a child wll not be able to make any effort to compensate for the myopia and improve their distant vision.
- Astigmatism: It is due to an inequality in the curvature of the cornea, insomuch as the rays focus on various points of the retina, affecting both near and far vision.
At birth, the human being does not have fully developed visual system. We aren't born with the ability to see, but rather with the ability to "learn to see".
Despite having complete eye structures, the visual system of a newborn is immature and develops as the cerebral cortex receives appropriate stimulation which is more or less symetrical in both eyes over the first few years of their lives.
The first few months of life are particularly important and can be separated in different stages.
- At birth, a baby's vision is limited to 20-30cm. They can only perceive light and dark sensations. Eye mobility is very reduced as is visual acuity.
- At 2-3 months, they already smile at start to following moving objects.
- From 3-4 months, depth perception begins, the child perceives a variety of colours, and starts to focus better.
- From 6 months, they can merge the two retinal images into one object obtaining binocular vision. From this time, the baby has learnt to use both eyes in a coordinated way and stops "squinting".
- It's not until the age of 8-9 years that the eyesight is fully developed, the first 4 years being those of greatest progression. In this period, the visual system is very vulnerable, so any cause that leads to poor vision in one or both eyes during childhood may result in a lack of visual function development leading to an amblyopia or "lazy eye" problem.
There is a series of signs and symptoms that may indicate the existence of a refractive issue and that would therefore be a reason to see your ophthalmologist:
- Blurred vision
- Constant blinking
- Headache and heavy eyelids
- Frequent red eyes and stinging
- That the child goes close to objects or is unable to read the board at school
- Leaning the head forward to focus their gaze (wry neck/torticollis)
First eye check-up
The first eye examination should be undertaken at birth by a paediatrician to rule out the presence of structural abnormalities or severe congenital eye problems.
Later on, despite there not being any apparent symptoms, a full eye examination by a specialist is advised aroun the age of 2-3, to assess the anterior and posterior segments of the eyeball, detect potential refractive errors and evaluate the status of the eye's motility to rule out the presence of strabismus.
The timing of further check-ups will depend on the findings from this first examination, and subsequently, even if no pathologies are found, annual check-ups are recommended until the age of 8-9, which is when visual learning is complete. From this age, we can space out the check-ups to every two years until the child is of legal age.
Treatment for refractive errors in childhood, be it hypermetropia (long-sightedness), myopia (short-sightedness) and/or astigmatism, is the use of glasses. For children, it is important that the glasses are well fitted, comfortable and stable.
In special cases, contact lenses can be used as treatment.
Depending on whether or not the child has a lazy eye (amblyopia), occlusion therapy (normally with a patch) will or will not be indicataed. The use of occlusion will depend on each case, according to age, the degree of amblyopia, etc.