Welcome Page
Terminology
The definitions of terms used in this web site.
Qualified hElp for yOu
Explanation of Terms Used at the Eyesight Laser Centre
Abduction - Movement of the eye outward from the straight ahead position.
Aberration - Blurred or distorted image quality that results from inherent physical properties (shape, curvature, density) of an optical device (lens or prism).
Ablation - the removal of material, similar to vapourisation. With respect to excimer laser 'ablation' represents a cold laser, gently yet totally removing eye material usually with no scarring.
ASA - Advanced Surface Ablation - is the refinement of photo refractive keratectomy PRK using more sophisticated techniques to produce a more accurate and more stable outcome. As in PRK, the surface epithelium is removed and allowed to regrow under a protective bandage contact lens.
Astigmatism - (uh-STIG-muh-tism) The visual defect attributable to the presence of an elliptical (i.e. that is egg or rugby ball shaped) rather than spherical shape in the refracting surfaces of the eye. This results in the diffusion of light rays with one axis being more in focus than the other.
bcva - Best Corrected Visual Acuity - A measure of how well a person can see after corrective treatment.
Cornea - (KOR-nee-ah) This is the clear structure at the front central part of the eye, imparting the greatest focusing power of all the ocular media.
Cyclotortional Movement - the reflex rotation of the eye ball when there is a change in posture, especially between sitting up and lying down.
Enhancement - a second treatment, usually 3 to 6 months after the primary treatment, which corrects for any minor adjustments.
Excimer Laser - An excimer laser is a cold laser which does not burn or cut. What it does do is vapourise tissue by breaking bonds between molecules, this means it is an extremely precise way of removing corneal material without causing damage.
Hyperopia - Long/far sightedness. In this visual defect the eye focuses rays of light at a focal point behind the retina. A hyperoptic eye is not able to clearly see objects that are nearby.
IntraLase™ - An advanced precision laser that is uses computer guided technology to bladelessly create the LASIK flap. The term is trademarked by IntraLase Corp.
Iris - The coloured portion of the eye, just behind the cornea, that provides the control of how much light enters the eye by expanding and contracting the 'black' opening (ie the pupil ).
Keratome - A knife (or blade) used for corneal incision.
Keratomileusis - (KER-uh-toh-mih-LOO-sis) a method of removing tissue from the centre of the optical zone in the cornea.
Keratopathy - (ker-uh-TOP-uh-thee) any abnormality with the cornea.
Keratoplasty - (KER-uh-toh-plas-tee) Replacement (transplantation) of scarred or diseased cornea with clear corneal tissue from a donor.
Keratotomy - Incision of the cornea.
LASEK - Laser Epithelial Keratomileusis - is a form of surface ablation in which the epithelial layer of cells (most superficial layer of the cornea) is treated with alcohol to allow it to be removed and the flap of epithelium is replaced but it eventually dies off due to the toxic effects of the alcohol. This is another form of surface ablation (see ASA or PRK ). Due to the toxic effects of the alcohol and the epithelial flap visual recovery is slower than with ASA or PRK.
LASIK - This is the acronym for Laser in situ Keratomileusis, a procedure for the correction of myopia, hyperopia and astigmatism in which the micro keratome is used to make a corneal flap, to provide access to the stromal bed of the cornea for the subsequent laser ablation.
Loss of bcva - Loss of Best Corrected Visual Acuity - This occurs when after refractive surgery treatment the patient can no longer see the same lowest line on the chart as they could before the treatment. For example; a patient with the best spectacle correction may drop from the 6/6 - 20/20 line to the 6/9 - 20/30 line. In general most patients are not concerned by small changes in loss of best corrected visual acuity (bcva) given the overall improvement in their vision.
Microkeratome - an instrument which cuts a predicted amount of tissue from across the cornea. This instrument acts in a similar fashion to a carpenter's plane.
Myopia - Short/near sightedness. Is the visual defect where the eye focuses rays of light at a focal point in front of the retina. A myopic eye is not able to clearly see objects that are in the distance.
Ocular - used to refer to items that are part of or associated with 'the eye', e.g. ocular movement = eye movement.
Presbyopia - (prez-bee-OH-pee-uh) - Is the physiological aging change, where the eye loses the ability to clearly focus when changing from distant objects to close objects.
PRK - This is the acronym for Photo Refractive Keratectomy. Now referred to as ASA (Advanced Surface Ablation). A procedure where excimer laser ablation of the surface of the cornea is used to correct myopia, hypermetropia and astigmatism (without the raising of a corneal flap - see LASIK ).
Pupil - A black circular opening in the front of the iris. The pupil can expand and contract to control how much light enters the eye.
Recurrent Erosion - is a superficial condition of the cornea where microscopic blisters form, which then break producing minute ulcers or erosions. These spontaneously heal within a few hours but produce a burning foreign body sensation while they persist.
Refract Refraction - The bending of light as it passes from one medium into another medium of different density (for example; as light passes from the air into the cornea). When testing a patient's vision, the ability to focus (bend light to form an image on the retina) is measured, hence the error is called a 'refractive error'.
Refractive Error - Strictly speaking, means parallel light rays are not brought to a sharp focus on the retina and so a blurred retinal image is produced. This means the image formed at the back of the eye is deformed because the eye parts are not focusing the light correctly.
Refractive Surgery - Any surgery which changes the way the eye refracts light is referred to as refractive surgery.
Stromal Bed - the material under the surface of the cornea.
Sources
Dr Michael Delaney
Dictionary of Eye Terminology, Barbera Cassin and Sheila Solomon (Melvin Rubin ed.) Triad Publishing Co. ISBN 0-937404-07-1
Budget Macquarie Dictionary, Pub: Macquarie Library Pty Ltd, 1982, ISBN 0-94975701-2
Dr M. Delaney