Woman with a refractive error wearing glasses

Refractive Errors

Living with nearsightedness, farsightedness or astigmatism

Refractive errors are the main reason why we seek the services of an optometrist or ophthalmologist. They describe irregularities in the way the light rays are bent (refracted) in the eye. In a healthy eye the light rays are bent to focus exactly at one point on the retina, creating a sharp, clear image. This state of perfect vision is called “emmetropia”. Refractive errors are optical imperfections that prevent the eye from properly focusing light on the retina, causing blurred vision.

The most common types of refractive errors are myopia (nearsightedness), hyperopia (farsightedness) and astigmatism.

What vision is like with myopia

Myopia simulation

Myopia

Living with nearsightedness

If you suffer from myopia, objects up close can be seen clearly; whereas distant objects appear blurry. Myopia is the most common eye condition in the world. In some areas almost half of the population is affected. Myopia, known commonly as nearsightedness, is a result of the eye having too much refractive power in relation to its length. In other words, the focal point of incoming light lies at a point in front of the retina, because:

  • the eye is too long, or
  • the cornea has too much curvature (less common). 

This results in faraway objects appearing blurry, because the light is not focused on the retina, where the optic nerve transmits the image to the brain.

Unlike hyperopia, the prescription and refractive power of myopia is given in negative dioptre; the more negative the number, the more severe your refractive error. Depending on your level of myopia, you may only be able to clearly see objects that are a few centimetres away from you, and in more mild cases, a couple of meters away.

  • Causes of Myopia

    Myopia usually begins to develop between the ages of 6 and 12. The likelihood of this vision defect increases if one or both of your parents are affected. The degree typically changes gradually every year, sometimes more frequently, until the ages of 14 to 16 for females and around 25 for males.

    While myopia cannot be prevented because the eye condition is hereditary or occurs during growth spurts, research is currently focused on slowing the progression of myopia. 

  • Symptoms of Myopia

    Common symptoms of myopia include:

    • Headaches from eye strain, for instance after watching TV or watching a movie in the cinema,
    • Difficulty focusing on distant objects, for instance while driving — particularly at night,
    • Frequent squinting and eye strain when trying to focus on objects in the distance. 

    Severe myopia can also lead to more degenerative changes in the back part of the eye such as retinal detachment. Therefore, it is important to diagnose and treat myopia. Both ophthalmologists and optometrists can recognize the vision defect from a basic eye exam.

  • Correcting Myopia

    If you suffer from myopia, there are several ways your vision could be corrected. You should consult your eye doctor to determine which options are suitable for you.

    • Glasses can be an easy way to improve your vision. Prescription glasses can fix refractive errors by altering the angle light rays enter the eye.
    • Contact lenses work under the same principles as glasses.
    • Laser eye surgery is another option to treat myopia. SMILE, LASIK and PRK/LASEK all treat refractive errors.
    • Intraocular lens (IOL) exchange, also referred to as refractive lens exchange, is an infrequently used option that a doctor may recommend to correct severe myopia in certain patients. This is a surgical procedure in which an artificial lens is transplanted in place of the natural lens – exactly like in case of cataract surgery, even though no cataract exists.
    • Phakic intraocular lens (PIOL) is when a lens is surgically placed in front of the existing natural lens to change the eye's optical power and correct the refractive error.

     

Hyperopia simulation

Hyperopia simulation

Hyperopia

Living with farsightedness

If you suffer from hyperopia, objects in the distance are usually seen as sharp; whereas close up objects appear blurry.

This condition, known as farsightedness, is a result of the eye’s shape being disproportional to its refractive power because:

  • the eye is too short (most common),
  • the cornea is not sufficiently curved (too flat), or
  • the natural lens is farther back in the eye than it should be.

The cornea and the natural lens normally refract incoming light rays to intersect at a single focal point that lies exactly on the retina, the layer of light-sensitive cells lining the back of the eye. A hyperopic eye refracts light to a focal point that lies behind the retina.

This causes vision problems, especially when trying to focus on objects at a close proximity. Blurriness occurs because the light is not focused on the retina, where the optic nerve transmits the image to the brain.

The prescription and refractive power of hyperopia is given in positive dioptre: the higher the number, the more severe your refractive error. Depending on your level of hyperopia, the distance you are able to clearly see varies between mild and severe cases.

  • Causes of Hyperopia

    Hyperopia usually develops at birth or at a young age, but only affects a small percentage of people until the age of 40. Then the number starts to increase. At a young age the flexibility of the natural lens can compensate for the refractive error by changing its shape and focusing the light rays exactly on the retina. This phenomenon is known as accommodation.

    Around the age of 40, the natural lens can become less flexible, which leads to the loss of its ability to compensate for the existing refractive error. Hyperopia becomes more noticeable and you begin using reading glasses, because it becomes harder to focus on close objects.
    The condition is often inherited, but may be caused in rare cases as a result of various local or systemic diseases.

  • Symptoms of Hyperopia

    If your degree of hyperopia is low, you might not notice your reduced vision. However, living without corrected hyperopia could negatively affect your quality of life. Hyperopia is a vision condition, not a harmful disease; the eye is still healthy.

    Common symptoms of hyperopia include:

    • Headaches from eye strain after reading, writing or working on a computer for a long period of time,
    • Difficulty concentrating and focusing on objects up close,
    • Fatigue or burning eyes,
    • Irritability or anxiousness while trying to concentrate.

    It is important to regularly have your eyes examined by an expert.

  • Correcting Hyperopia

    If you suffer from hyperopia, there are several ways your vision can be corrected. You should consult with an ophthalmologist or optometrist to determine which options are available to you. The most common ways are as follows:

    • Glasses can be an easy way to improve vision. Prescription glasses can fix refractive errors by altering the angle light rays enter the eye.
    • Contact lenses are another option to correct your vision. These work under the same principles as glasses.
    • Laser eye surgery is another option to treat hyperopia. LASIK and PRK/LASEK are options to treat a refractive error. This procedure is only possible if the refractive error is below 3.00 dpt.
    • Intraocular lens exchange, also referred to as refractive lens exchange or refractive lensectomy, is an additional option that the doctor may recommend. It means replacing the natural lens when no cataract exists.
    • Phakic intraocular lens (PIOL) is when a lens is surgically placed in front of the existing natural lens to change the eye's optical power and correct the refractive error.

     

Astigmatism simulation

Astigmatism simulation

Astigmatism

Close and distant objects appear skewed or distorted

In addition to myopia and hyperopia, many people also have an astigmatism. This condition occurs when the curvature of the cornea, the transparent part of the front of the eye, is uneven and slightly oblong – similar to an American football. In contrast, a normal cornea is evenly shaped all around like a basketball. Due to the unevenness of an astigmatic cornea, incoming light rays are refracted by the cornea in different angles.

Instead of one focal point like in normal vision, there are multiple focal points in an eye with astigmatism. The disarray of focal points fails to make a single, clear image on the retina, the layer of light-sensitive cells lining the back of the eye.

Without a focused image on the retina, the information sent to the brain through the optic nerve is distorted. This results in skewed or crooked images both near and far. Depending on the type of astigmatism, images appear stretched horizontally or vertically.

  • Causes of Astigmatism

    Like myopia and hyperopia, astigmatism is a refractive error: the eye has problems focusing light properly. Instead of focusing light rays on a single focus point on the retina to produce clear vision, light rays are focused at multiple points – either in front of the retina or behind it (or both).

    Astigmatism may also exist if the natural lens is irregularly shaped (lenticular astigmatism). It could also be a symptom of a disease known as keratoconus, which is recognizable when the eye begins to bulge. It develops when weak fibers that form and support the cornea, begin to break.

    Astigmatism is either present at birth, during early childhood, or could develop after a trauma, injury or disease. If one or both parents have the condition, it increases the likelihood of suffering from it too.  

  • Symptoms of Astigmatism

    Astigmatism can affect sight in different ways depending on how the cornea is shaped: vision could be distorted in a horizontal, vertical and/or diagonal direction.t

    This condition can occur independently or be accompanied by myopia or hyperopia. Astigmatism is a vision condition, not a harmful disease; the eye is still healthy. Typical symptoms of uncorrected astigmatism can be eye strain and headaches, which mostly occur after reading or other prolonged visual tasks such as working on the computer. A very common symptom is squinting.

    Your ophthalmologist or optometrist can recognize astigmatism in a routine check-up exam. If you are diagnosed with astigmatism, it is likely that you will need glasses, contact lenses or laser eye surgery. 

  • Correcting Astigmatism

    If you suffer from astigmatism, there are several ways your vision could be corrected. You should consult with an ophthalmologist or optometrist to find out which options are available to you. The most common ways are as follows:

    • Glasses can be an easy way to improve your vision. Your prescription glasses can fix your refractive error by altering the angle the light rays enter the eye.
    • Contact lenses are another option to help you see. These work under the same principles as glasses.
    • Laser eye surgery is an option with high success rates. The three generations of refractive eye laser procedures treat astigmatism: SMILE, LASIK and PRK/LASEK. Like all surgeries, refractive laser surgery is not without risks.
    • Refractive lens exchange or refractive lensectomy replaces the natural lens with an intraocular lens (IOL), specifically a toric lens.

    Read more on the following pages if any of these treatment options are relevant for you.

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