Vision disorders

About vision and its function

The cornea, the iris, the lens and the retina are the key elements that allow light entering the eye to be transformed into the images perceived by our brain via the optic nerve.

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Light stimuli are first absorbed by the cornea, a curved, transparent lens situated in front of the iris (sphincter which contracts or dilates depending on the amount of light perceived), before passing through the flexible crystalline lens. Then, the rays of light converge at a single point to form an image on the retina, the membrane lining the rear wall of the eye. Subsequently, the optic nerve transmits this new visual information to the brain, where it is decoded to form an image.

The cornea, the transparent front part of the eyeball, allows light to be transmitted to the lens and the retina. When the light cannot be focused directly and precisely on the retina, and is instead focused in front of it (myopia) or behind it (hyperopia), this is called a refractive error.

Refractive laser surgery can remodel the cornea in order to adjust its curvature and thus correct vision problems (also known as ametropia) such as myopia, hyperopia, astigmatism and presbyopia. After surgery, the patient becomes emmetropic, which means that they will no longer need to wear glasses or contact lenses on a daily basis. Surgery involving the insertion of an intraocular implant is performed in cases where laser surgery is contraindicated, for example if the patient’s cornea is too thin.

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Myopia is the most common refractive issue. It is caused by the eye being too long and/or the cornea being too curved. It results in distance vision becoming blurry.

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Hyperopia results in difficulty focusing. It is caused by the eye being too short and/or the cornea being too flat. This means additional focussing power is required in order to see clearly, which is referred to as accommodation. People with hyperopia have better distance vision than near vision.

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Astigmatism is an error in the curvature of the cornea. Instead of being spherical, the cornea is oval instead. People with astigmatism have poor distance and near vision.

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Presbyopia is a common visual defect in individuals aged over 40. This vision problem becomes evident as the eye ages. It results in a progressive deterioration of near vision with age.

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