Refractive errors

Myopia (short-sightedness or near-sightedness)

When light rays enter the eye, they should normally be focused on the central fixation point (macula) of the eye in order for the eye to produce clear vision.

In a myopic eye, the eye is too long for light rays to be focused accurately on the macula. Images are formed in front of the macula instead, resulting in blurred vision. In myopic people, distance vision is blurred unless they wear visual aids like glasses or contact lenses. 

Glasses or contact lenses re-direct light rays entering the eye so that they focus accurately on the macula, producing clear vision.

High myopia is more than just having to wear thick glasses. Highly myopic eyes are more likely to develop serious complications like retinal tears, retinal detachments and early macular degeneration (myopic degeneration) which can result in blindness. They are also more likely to develop glaucoma, early cataracts and floaters. This is because of structural abnormalities in myopic eyes.

LASIK surgery can be done to reduce the myopic “power error” so that vision can be clear without the use of glasses or contact lenses. However, even after myopia has been removed by LASIK, the eye remains prone to the complications mentioned above because LASIK only corrects the “power error” but does not rectify the structural problems with highly myopic eyes.

Myopia is an extremely common eye disorder in Asians, but myopia in young children can now be controlled with atropine eye drops.

Hyperopia (Long-sightedness or Far-sightedness)

In a hyperopic eye, the eye is too short for light rays to be focused accurately on the fixation point of the eye (macula). Images are formed behind the macula instead, resulting in blurred vision. 

In hyperopic people, distance vision is clear and correction is needed for near viewing. Glasses or contact lenses will be able to improve vision; LASIK will also be able to correct the abnormal “power” of the eye and provide good vision without the need for glasses or contact.

Astigmatism   

In astigmatism, the eye is not a perfect sphere (like a football) but develops in a more oval or irregular shape (like a rugby ball). The uneven surface of the eye causes focusing of light rays onto different points within the eye, resulting in blurred images or multiple images.

Vision in all distances may be blurred, and correction with glasses or contact lenses will be needed to improve vision. LASIK can also be done to rectify this “power error”.

Presbyopia      

The natural lens of the eye helps to focus light rays onto the central fixation point (macula) of the eye. In a young person, the lens is flexible and changes shape as it adjusts automatically for near and far distances. A young eye is like a camera with a very fast and accurate auto-focus function.

With increasing age, the natural lens gradually loses its flexibility. This means that the “auto-focus” function of the eye gradually slows down and eventually stops working. It becomes more difficult to focus on near objects as we age. 

This condition is presbyopia. It is a natural part of ageing and happens to everyone, usually after the age of 40 years. As reading at near becomes more difficult, reading glasses (bifocal glasses or progressive glasses) will start to become necessary for comfortable near viewing.