About the Eye

How the Eye Works

eye and camera

The eye functions on much the same principle as a camera.

The iris, or coloured portion of the eye, acts as the shutter to regulate the amount of light admitted to the eye.

The cornea (the clear window at the front of the eye), and the lens (located behind the pupil), focus light rays, from the object being viewed, onto the retina at the back of the eye.

The retina then transmits the "picture" of the object viewed to the brain where the object is "seen".

Refractive Error

For the eye to present a clear image, the light rays entering the eye need to come to focus on the back of the eye.

If rays of light do not focus on the back of the eye, a blurred image is transmitted to the brain.

This is correctable by glasses or contact lenses and is known as a refractive error.

Refractive errors can be the result of a number of factors, which include:

The three categories of refractive errors are: myopia (short sightedness), hypermetropia (long sightedness), and astigmatism. These may be corrected by refractive surgery.

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My Refractive Error

example prescription

This is a sample of what your optical prescription may look like

Sphere (Sph) negativeis Myopic
Sphere (Sph) positiveis Hypermetropic
Cylinder (Cyl)Amount of Astigmatism
AxisOrientation of Astigmatism

Prescriptions format may vary but the information is the same.

The Distance line is the refractive error of your normal vision

The Near line is your Presbyopic error or reading correction

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Myopia (Short-sight)

Myopia is a very common defect affecting approximately one in five adults.

Without their spectacles short-sighted people are able to see near objects clearly if held at the appropriate distance, but usually objects beyond arms length are "blurred" or "out of focus".

Normally, spectacles or contact lenses are used to correct myopia. People with moderate to high levels of myopia are unable to see anything of real value without their glasses. If you wear myopic spectacles then by holding them a few inches away from a printed page you will note that they make everything seem smaller.

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Hypermetropia (Long-sight)

Long-sighted people are able to see images in the distance more clearly than close images. They may however, be unable to see at either distance clearly without the need glasses.

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People with astigmatism have a cornea that is not entirely spherical giving a distorted or blurred image at all distances.

Can be found alone or in conjunction with myopia or hypermetropia.

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The term used to describe the need for reading glasses which usually occurs in middle age as a result of ageing changes within the eye’s natural lens.

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My Suitability for Treatment

To be suitable for refractive surgery your spectacle prescription or contact lens prescription should be stable, i.e. it should not have changed significantly in the past two to three years.

This generally means that patients are 21 years of age or older.

Patients should have realistic expectations regarding expected outcomes. If you have a low or moderate degree of refractive error you should expect very good results. Those with higher degrees of refractive error may still need a reduced correction for some activities.

Patients should have no significant ocular disease.

You will need to undergo a consultation which will include a thorough eye examination. This involves a detailed examination of the health of your eyes and an assessment of your suitability for surgery.

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