Laser Eye Surgery Glossary

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    The complex shape of the cornea can mean there are many different factors that can cause distortion or blurring of the viewed image. It is possible to derive the individual contributing factors that cause these distortions. These are called aberrations. Lower order aberrations (such as 'Sphere' or 'Cylinder') are corrected by glasses or contact lenses or standard laser procedures such as LASIK laser eye surgery. Higher order aberrations (such as 'Coma' or 'Trefoil') can only be corrected by the latest Wavefront laser eye surgery treatments.


    Measuring the extent of a person's optical aberrations using a diagnostic instrument known as an aberrometer.


    In laser eye surgery, to remove.


    The vaporization of tissue with the excimerExcimerEXCited diMER - The type of laser used in laser eye surgery. laser. Further reading

    Ablation zone

    The area of tissue that is removed during laser eye surgery. Further reading


    See corneal abrasion.


    The ability of the eye to change its focus from distant objects to near objects.


    See visual acuity.


    Calculations that have taken into account various factors. When applied to laser eye surgery software this means the calculations should allow for the factors and correctly predict the change that is made in the patient's prescription.

    Ambient Illumination

    Brightness of surrounding level of light.


    Clinical name for a lazy eye, blind or low-functioning eye. Many patients with amblyopia can still be treated with laser eye surgery, although the underlying difference in vision between the two eyes will still remain. Further reading


    Anaesthetic eye drops are used during laser eye surgery to numb the eye for about an hour, with no injections required. Further reading


    A difference in image size between the two eyes. Further reading


    A significant difference in refractive power between the two eyes, usually where the variance is at least one dioptre. Further reading

    Anterior chamber

    The fluid-filled area between the cornea and the lens. Further reading

    Anterior uvetitis

    Inflammation at the front of the eye. Further reading


    Drugs taken in the form of drops or ointments which reduce the inflammation and aid in pain relief. Further reading

    Aqueous humor

    The fluid in the anterior chamber. Further reading

    Artificial Lens Implant (ALI)

    This vision correction treatment involves the implant of a soft, synthetic lens into the eye. This will act in the same way as a standard contact lens, staying in place to help the eye to focus clearly.


    A refractive error caused by an irregular shape of the cornea (much like a rugby ball). Astigmatism is measured in terms of dioptres, and axis. Uncorrected astigmatism may produce ghosting or double images. Further reading


    In ophthalmology, a line that is the symmetrical centre of a curved optical surface. Measure of astigmatism.

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