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Dry Eye Syndrome Dry Eye Syndrome

How the eye works


The eye functions in a similar way to a camera, using light to form images. The cornea (clear window at the front of the eye) provides two thirds of the focusing power. The lens located behind the iris and pupil provides one third. Combined, these focus the light rays to create an image on the retina at the back of the eye. The retina converts the light rays into electrical messages that are sent to the brain via the optic nerve, enabling us to 'see'.


Our eyes can be affected by a variety of conditions which reduce the quality of our vision and require the wearing of glasses or contact lenses to correct the problem. Some of these refractive conditions can be overcome with laser surgery.


Myopia – Short-sightedness

Myopia is when the focusing power of the eye is too strong relative to the length of the eye, causing light rays to focus in front of the retina. Typically, close vision is clear but distance vision is blurred.



Hyperopia – Long-sightedness

Hyperopia is the opposite of myopia. The focusing power of the eye is too weak relative to the length of the eye, causing light rays to focus behind the retina. Near vision is more difficult than distance and both may be blurred.






Astigmatism is where the cornea is not completely spherical in shape. Instead of being round like a soccer ball, the cornea is oval like a rugby ball. The light rays are focused at multiple points instead of one precise point on the retina. This results in blurred vision at any distance.



Presbyopia is a natural ageing condition of the eye. The lens of the eye progressively thickens and loses its flexibility. This makes it difficult to focus up close, becoming noticeable after the age of forty and is corrected by reading glasses.


Correcting refractive errors through laser surgery

Myopia, Hyperopia and Astigmatism are normally corrected by wearing glasses or contact lenses. Laser refractive surgery changes the curvature of the cornea and can correct most cases of myopia, hyperopia and astigmatism. Myopia is corrected by making the cornea flatter, while Hyperopia is corrected by making the cornea more curved. In the case of Astigmatism, the cornea is made more spherical in shape. Presbyopia can now be corrected with PRESBYOND®



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