Uncorrected refractive error

Uncorrected refractive error is the most common cause of vision impairment, and the second leading cause of blindness in the world. Uncorrected refractive error needs to be diagnosed by an eye care professional, after a dilated eye examination. Read on to learn more.

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What is uncorrected refractive error?

Refractive error happens when an eye is misshapen, preventing successful refraction. Uncorrected refractive error is when we don't do anything about it.

Refraction is when the eye bends light so that it can pass through the sections of your eye; the cornea, the lens, and eventually the retina. The retina is the thin, light-sensitive tissue at the back of the eye.
 

Image credit: National Keratoconus Foundation

In order to process what we see every day, the brain needs to receive messages from the retina, sent through the optic nerve. If your retina doesn't receive light-rays correctly, it won't be able to pass messages to the optic nerve and then to the brain for interpretation. 

If this happens, images can appear blurred or unclear, resulting in vision loss.

When does refractive error happen?

Refractive errors can happen when the eyeball grows or reduces in length, when the cornea changes shape, or simply with age. 

Overuse of the eye does not cause refractive error. Rather, if refractive error runs in your family, you may have more chance of developing a condition.

People of all ages are affected by refractive errors, but some conditions are more common in certain populations. For example, presbyopia is present in most adults over 35-45, while myopia is more common among Asian people!

We often use glasses to correct long or short sightedness caused by refractive error, as well as the inability to change focus properly.
 

Read more information about the biology of the eye

What are the main types of refractive error?

Myopia (near sightedness or short sightedness)

Usually an inherited eye condition, myopia causes far away images to be seen blurred, while images are clear up close. This happens because the distance between the cornea and the retina is too long. So, instead of the light focusing on the retina, it focuses in front of the retina.

Myopia is usually identified during childhood and exacerbated during puberty, when the body goes through a lot of change.
 

Hyperopia/ hypermetropia (far sightedness or long sightedness)

Hyperopia - sometimes called hypermetropia - occurs when the distance between the cornea and the retina is too short. This causes the light rays to focus behind the retina, rather than on it.

We experience hyperopia on a scale; mild levels make images appear blurred close up, and clear when they're far away. For individuals with high levels of hyperopia, images can be blurry at all distances.

In childhood, hyperopia can be difficult as children may not always notice their vision problems until they are older.
 

Presbyopia (loss of near vision with age)

Presbyopia is one of life’s inevitable burdens brought on by the ageing process.

As we age, our lenses become rigid, allowing less close-range focusing flexibility. Signs of presbyopia start to emerge from around 35-45 years of age. Presbyopia is a normal result of the ageing process, unfortunately, but can be corrected by using reading glasses.
 

Astigmatism (uneven focus)

When the cornea has asymmetric stigmatism (uneven curvature), we call that astigmatism.

Rather than the equal curves of a sphere, the front surface of the eye ends up more like a football. This causes the light coming through the cornea to focus unequally on the retina, resulting in a distorted or ‘stretched out’ image. In most cases, a person with astigmatism will have blurred vision both near and far.

Symptoms of uncorrected refractive error

Some of the symptoms of uncorrected refractive error are:

• Blurred or distorted vision
• Headaches, squinting and eye strain
• Difficulty reading
• Double vision
• ‘Halos’ around bright lights
• Haziness

Uncorrected refractive error needs to be diagnosed by an eye care professional, after a dilated eye examination.

How is refractive error treated?

There are a few simple solutions that are available to correct refractive error, including eyeglasses, contact lenses, or different kinds of surgery.

Eyeglasses (spectacles) are the most common and simple solution. An eye care professional can measure you for a pair of eyeglasses for effective correction.

Contact lenses are a less common, but still popular treatment for correcting refractive error. They work by placing an artificial lens on the film of tears covering the eye’s surface.

A contact lens is thin, curved and in most cases these days, soft and bendy. Like eyeglasses, you'll need to have your contact lenses fitted by a professional. Your optometrist will be able to give you lessons on safe, clean insertion of contact lenses. 

But remember, always seek out professional advice if you think you need contact lenses, as you won't be able to wear them with some eye conditions.

Corrective surgery is also necessary for some patients. Corrective surgery options include refractive (laser) surgery and intraocular lens (IOL) surgery.

Refractive surgery, of which there are many types, can be used to correct the vision of those with refractive error. Laser surgery is one type of refractive surgery.

Experts use specialised tools to measure the surface contour of your eye and then permanently reshape the cornea (front surface of the eye). They do this by vaporising the surface tissue into a new shape, restoring the eye’s ability to focus light rays directly on the retina.

Intraocular lens (IOL) replacement surgery is another kind of refractive surgery available. Surgeons remove the natural lens from the eye and replace it with an artificial lens called an intraocular lens (IOL). IOLs are also used in cataract removal surgeries.