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The most common definitions - refractive errors
10/26/2017
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The most common definitions - refractive errors
10/26/2017

Nearsightedness...myopia...farsightedness...hyperopia...astigmatism - sometimes it’s easy to mix up the most common results of eye examinations for children, especially after you get home.




 

Nearsightedness is also known as myopia.  In the most simplistic sense, it means it is harder to see further away than it is up close.  In the more technical sense, it means that images that enter the eye focus in front of the retina - the sensory back layer of the eye - instead of right on it.  This occurs either because the eyeball itself is too long, or the cornea (the front of the eye) is too curved.  


While most of the development of myopia is physiologic and unknown, children are more likely be nearsighted if one or both of their parents are nearsighted; as well, in this digital age, there is more evidence showing that longer times at intensive near work like computer use, increase the risk of nearsightedness as well.


The way glasses - or contact lenses - help in seeing clearly, is moving the focus of images from in front of the retina, onto the retina itself.



Farsightedness is also known as hyperopia.  Very simply, closer images are harder to focus on than objects at a distance, but it very much can affect both.  Technically in this case, images focus behind the retina rather than on it.  


The best way of thinking of farsightedness is the eyes being too ‘weak’.  Often, children focus (‘accommodate’) to compensate for the weakness, which can strain the visual system if in too high an amount, and past a certain level it can’t be overcome.  This is one of the reasons comprehensive examinations are so important, because often far sighted children will have ‘perfect’ vision just from reading a chart.


In the exact opposite of nearsightedness, glasses help in this case by moving the focus forward onto the back of the eye.




Astigmatism is always the most confusing one to understand.  It is not a disease of the eye, but like myopia and hyperopia is another type of ‘refractive error’ of the eye.  In astigmatism, the front of the eye, or the lens of the eye, has a different curvature - often likened to a football.  People who have simple nearsightedness, farsightedness, or no refractive error at all, have one point that the images enter the eye focus at.  In astigmatism, there is now two, because of that football shape - the two different curvatures.


In terms of what a child sees, things are distorted far and near, more in one orientation than another.


Glasses and contacts help in this case by moving both of those focusing points onto the back of the eye, the lenses themselves having different curvatures just as the eye does.





While there are many other issues with children’s vision that can be discovered by one of our optometrists at the Eye Gallery during a comprehensive eye examination - from binocular vision issues to health issues - the need for glasses to correct these “refractive errors” is the most common.  Be sure to ask any questions to help understand your child’s visual needs!

 
Saskatoon Optometrist