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Myopia, Hyperopia, Astigmatism


Refractive error is a common vision problem. It occurs when the eye cannot clearly focus images onto the back surface of the eye (i.e the retina). This results in blurring of vision.

Changes in the length of the eyeball (longer or shorter), shape of the cornea or density of the crystalline lens within the eye, or ageing of this lens can cause refractive error. A common type of refractive error seen in Singapore is myopia. Refractive error can affect your daily activities and mobility if it is severe and uncorrected.


What are the types of refractive error?


The three common types of refractive error are: 

1. Myopia (short-sightedness)
2. Hyperopia (long-sightedness)
3. Astigmatism

To understand these refractive errors better, it helps to understand:


What happens to light rays when they enter the eye?

The light rays from an object enter the eye through the pupils, passing through the crystalline lens which helps to focus these rays onto the retina (the back surface of the eye). The retina then collects this information and sends it to the brain for interpretation. Therefore, if light rays are not well focused onto the retina, images will not be clearly seen.


What is myopia ? (short-sightedness / near-sightedness)

Myopia occurs when light rays are focused in front of the retina rather than on the retina. This could be due either to a long eyeball or to too much focusing power of the eye. It causes distant objects to be blurry while near objects remain clear.

Myopia can develop at any age and optical correction such as glasses or contact lenses can help to improve the quality of vision. Myopia tends to progress in variable amounts in childhood and stabilizes by the late teens to early twenties. Read more about Atropine eye drops for myopia.


What is hyperopia? (long-sightedness / far-sightedness)

Hyperopia occurs when light rays are focused behind the retina rather than on the retina. This could be due either to a small/short eyeball or to too little focusing power of the eye. It causes both near and distance objects to be blurry.

Low to moderate amounts of hyperopia are common in childhood. Low to moderate hyperopia in a child can easily be compensated by the child's own focusing mechanism (termed "accommodation"), thus spectacles are usually not needed. Hyperopia in childhood progressively decreases as the eyeball lengthens with childhood growth.

High hyperopia in childhood may require spectacle correction, particularly when this hyperopia is associated with eye misalignment ("convergent squint") or lazy eye. Moderate to high hyperopia in adults usually require spectacle correction.


What is astigmatism?

Astigmatism occurs when the cornea is more curved in one direction than in the other, resulting in light rays that are focused at several points in front of and/or behind the retina. This leads to a distorted image and is perceived by the patient as a blur image. The curvature differences that cause astigmatism can be easily understood when a normal eye is thought of as a perfectly shaped round basketball whereas an astigmatic eye is irregularly shaped like a rugby ball. Near and distant vision can both be affected. Optical aids can be prescribed for significant astigmatism.


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Singapore 329563

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