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Refractive Errors

In a normal eye, light rays pass through the cornea and lens and focus on the retina, and a sharp image is perceived by the brain. It is like a camera lens focuses light onto a film.

Refractive errors occur when light rays pass through the eye but cannot focus on the retina and blurred images are formed. This is due to factors such as shape of the cornea, lens and length of the eyeball.

Types of Refractive Errors:
Near-sightedness (Short-sightedness)

A near-sighted eye is longer than normal, so light rays focus in front of the retina. Close objects can be seen more clearly while distant objects look blurred.

Far-sightedness (Long-sightedness)

A far-sighted eye is shorter than normal, so light rays focus behind the retina. Distant objects can be seen better while close objects look blurred.


Many people with myopia or hyperopia have some degree of astigmatism. This is caused by uneven curvature of the cornea or lens. Astigmatism distorts the light rays entering the eye and focus unevenly on the retina. Objects look distorted and blurred.


In a normal eye, light rays of close objects focus behind the retina, which is similar to a far-sighted eye looking at distant objects. The lens of a normal eye can change its shape and therefore refocus light rays on the retina, so a sharp image is formed. This process is called accommodation and it is automatic. With increase in age, the lens of the eye loses its flexibility and becomes less able to change its shape to accommodate. When people reach forties, tasks such as reading small prints become difficult.

Treatment for Refractive Errors in adults
1. Use of glassess / contact lens
2. Refractive

Prevention of progression of short-sightedness in children
While wearing spectacles or contact lenses can improve vision for children with short-sightedness, both methods may cause inconvenience and wearing contact lens may even give rise to complications.

High myopia is associated with higher chance of eye diseases, such as retinal detachment, macula haemorrhage, cataract and glaucoma etc.

The causes of short-sightedness progression. Both genetic and environmental factors play a role. Short-sightedness progression is more significant in children between 6-12 years old.

1. Atropine eye drops
Studies on the effectiveness of atropine eye drops(0.5% to 1.0%) in reducing short-sightedness progression started as early as in th 70s. Atropine is a non-selective anti-muscarinic blocker. It can inhibit excessive scleral growth and thus reduce or arrest short-sightedness progression. Studies showed that 0.5% and 1.0% atropine eye drops can slow short-sightedness progression by 75% and 80% respectively. On the other hand, atropine will cause pupil dilation and inhibit accommodation (zooming of focus to see near things). Photochromatic and progressive lenses may be required in children using atropine eye drops.

Recent studies showed that using lower concentration of atropine eyedrops (0.01% to 0.1%) can slow short-sightedness progression with less side effects. Atropine (0.01%) can reduce progression by 60%, but the average increase in pupil dilation is only about 1mm and 95% of children do not require progressive lenses for near vision.

In summary, topical atropine can slow down short-sightedness progression in children. However, its application has to be considered on individual basis. Regular monitoring is needed when using the eyedrops.

2. Can progressive lens arrest or reduce short-sightedness progression?
One of the hypotheses of preventing short-sightedness progression is to control accommodation. Progressive lens is a specially designed lens to achieve this purpose. A progressive lens is a one-piece lens whose short-sightedness power varies gradually from a highest value in the upper portion to a lowest value in the lower portion. The child is asked to use the upper portion for viewing distant objects and the lower portion for nearer objects. However, the evidence for arresting or preventing short-sightedness progression by progressive lens is very weak and not well established.

3. Can contact lens arrest or reduce short-sightedness progression?
Some studies found that there was no difference in short-sightedness progression between children wearing Rigid Gas Permeable (RGP) lens and those wearing spectacles. Orthokeratology (Ortho-K, OK lens), which was introduced in the 70s, uses tight-fitting, flat, rigid contact lenses to decrease the curvature and refractive power of the cornea. Lenses are changed periodically to progressively flatter ones. After the cornea has been sufficiently flattened, retainer lenses are usually worn at night to preserve the modified shape, otherwise the eye will revert back to the original corneal curvature and refraction. Parents must be aware that there are potential risks associated with contact lens wearing, such as corneal abrasion, ulcer and infection, leading to permanent loss of vision.