You’ve been told your child (or you) has an eyesight issue but you don’t quite understand what it means? See below for explanations of the most common kinds of eyesight terms…
What causes eyesight problems?
We see the world around us because of the way our eyes bend (refract) light. Sometimes eyes can’t properly focus light, causing blurred vision. The main problems are nearsightedness, farsightedness and astigmatism.
These problems can usually be “corrected” with glasses or contact lenses.
What is myopia or short-sightedness?
Someone with myopia has blurry distance vision, but generally has good near vision. In high myopia (i.e. someone who is very myopic), even near vision is affected. In this case, objects must be extremely close to the eyes to be seen clearly, so glasses would likely be needed even for close work like reading. Either one or both eyes can be myopic, and the eyes can be different strengths. This means a person may not know they have a vision problem, as one eye may have been compensating for blurred vision in the other eye without them even realising.
Source: Public Domain, https://commons.wikimedia.org/w/index.php?curid=1817263
What is hyperopia or far-sightedness?
Far-sightedness, also known as hyperopia, is a condition of the eye where light focuses behind, instead of on, the retina. This causes close objects to be blurry, while far objects may appear normal. In stronger cases, even objects at all distances may be blurry. Other symptoms may include headaches and eye strain.
Because far objects are generally clear, a child may not realise they have far-sightedness. In some cases, the additional work the eyes need to do to generate a clear image of closer objects such as words on a page can lead to letters becoming jumbled up, or frequent loss of concentration such as losing their place on the page.
Far-sightedness is usually corrected with convex corrective lenses, which help to focus light on the cornea.
What is astigmatism?
In a person with astigmatism, vision may be blurred both close-up and at a distance. Astigmatism usually is caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball), it is shaped more like a football. In an eye with astigmatism, light fails to come to a single focus on the retina to produce clear vision. Instead, multiple focus points occur, either in front of the retina or behind it (or both). What this might look like for a person with astigmatism varies depending on the type of astigmatism but some examples are shown below.
What is amblyopia or lazy eye?
Amblyopia, also known as lazy eye, is a vision development disorder in which an eye fails to see clearly, even with prescription eyeglasses or contact lenses. The cause of amblyopia can be any condition that interferes with focusing during early childhood. This can occur from poor alignment of the eyes, an eye being irregularly shaped so that focusing is difficult, one eye being more nearsighted or farsighted than the other, or clouding of the lens of an eye. Even after the underlying cause is fixed, the child may not re-gain perfect vision, at least until the brain gets used to the new information it is receiving.
Early detection improves treatment success. Glasses may be all the treatment needed for some children. In other cases, treatments which force the child to use the weaker eye are used. This is done by either using a patch or putting atropine in the stronger eye. Without treatment, amblyopia typically continues into adulthood.
What is strabismus or turned eye?
In a person with strabismus, one eye looks directly at the object they are viewing, while the other eye is misaligned. Strabismus typically involves a lack of coordination between the eye muscles.
Newborns often have intermittent crossed eyes due to incomplete vision development, but this often disappears as the baby grows and the visual system continues to mature. Most types of strabismus, however, do not disappear as a child grows.
Generally, the earlier strabismus is detected and treated following a child’s eye exam, the more successful the outcome. Without treatment, your child may develop double vision, amblyopia or visual symptoms that could interfere with reading and classroom learning.
What is colour blindness?
Colour blindness is the decreased ability to see colour or differences in colour. Colour blindness can make some educational activities difficult. Buying fruit, picking clothing, and reading traffic lights can also be more challenging. Problems, however, are generally minor and most people adapt.
There is no cure for colour blindness. Diagnosis may allow a person’s teacher to change their method of teaching to accommodate the decreased ability to recognize colour. Special lenses may help people with red-green colour blindness when under bright conditions. There are also mobile apps that can help people identify colours.
Males are more likely to be colour-blind than females. Boys are screened for colour-blindness in NZ as part of routine vision screening at age 11 or 12.
What do colour-blind people see?
It depends on the type of colour-blindness, but most common are difficulties in differentiating reds and greens. In the first picture below, depending on the computer displays, people with normal vision should see the number “74”. Many people who are colour blind see it as “21”, and those with total colour blindness may not see any numbers.
Source: Wikipedia Public Domain https://commons.wikimedia.org/w/index.php?curid=1692985
Simulation of the normal (above) and dichromatic (below) perception of red and green apples. By w:en:User:Limbicsystem – English Wikipedia, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2547605