Types of refractive errors of the eye

The words ‘refractive error’ sounds more like a computer error message than a description of the eye but what do we mean by this phrase?


A refractive error means that the eye isn’t focusing the light perfectly on the retina to form a focused image so it might appear blurry.

When the optician measures eyesight they call this part of the test the ‘refraction’ as they’re looking for any refractive error and they will find some in most patients. Glasses are only normally prescribed if they will improve either the patient’s vision or comfort.



The different types of refractive errors


Are all refractive errors the same? No, broadly speaking there are four key errors that optometrists looking for:


1. Myopia (short sightedness)


This is where the eye is longer than normal or the cornea is too steep, meaning that light rays focus in front of the retina. In real terms this means that near objects are clear, but distant objects appear blurred.


2. Hyperopia (long sightedness)


This is where the eye is shorter than normal or the cornea is too flat, meaning that light rays focus behind the retina. In real terms this means that near objects may be blurrier than distance objects. The eye muscles in younger patients can work to achieve clear vision at all distances and so glasses may make the vision more comfortable rather than clearer. This explains why some children find it hard to understand why they need to wear their glasses!


3. Astigmatism


This describes the need for power to be prescribed to correct the shape of the eye. You can think of it as the cornea on the front of the eye being shaped a bit like a rugby ball (as opposed to a special football). This means that the light rays aren’t all focused on the retina, so a special lens must be made. You can be short sighted or long sighted and have astigmatism and it too can run in families!


4. Presbyopia


This will probably come to us all at some point and basically means that the eye is getting older. The lens within the eye can no longer change shape easily to focus an image on the retina when we’re looking at something close to us, so it appears blurry. This means that most patients will need reading glasses which are made progressively stronger as the lens and muscles in the eye change gradually. Patients normally notice these changes most between the ages of 40 and 60.


Have you been diagnosed with a refractive error condition?


So, you’ve been told you have a refractive error. Can anything be done about it? The simple answer is, yes!


There are a fantastic range of lenses available now so that nearly any prescription can be corrected with a spectacle lens (these can be single vision, bifocal, varifocal options and more). There are so many different frames to with rimless, plastic, metal, large, square, sparkly, shiny, designer and many other options to choose from you can have lots of fun deciding what’s best. And just when you thought you’d made your decision there are sunglasses to think about too.

Always consult a qualified optometrist to confirm a diagnosis!

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