Glossary of Terms
ABERRATION – Any optical defect and/or design error which causes any of the processed light to deviate from the focal point, reducing the quality of the image.
ABLATION – The removal or destruction of tissue.
ACCOMMODATION – Increase in optical power by the eye in order to maintain a clear image (focus) as objects are moved closer. Natural loss of accommodation with increasing age is called presbyopia.
AMBLYOPIA – Impaired vision in one or both eyes that cannot be remedied with corrective lenses and has no obvious organic cause in the structures of the eye or visual pathway (colloquially known as “lazy eye”)
AMETROPIA – General term for conditions in which the eye does not focus properly but can be corrected with eyeglasses or other vision aids (ie myopia, hyperopia, astigmatism, presbyopia)
ANISOMETROPIA – Uneven refractive power of the two eyes, usually denoting more than a 1-diopter difference.
ANISOCORIA – Uneven size of pupils in the two eyes, usually reserved to describe more than a 1-mm difference in diameter.
ASTIGMATISM – Visual defect attributable to the presence of an egg- or football-shaped, rather than spherical shape, in the refracting surfaces of the eye, resulting in the diffusion of light rays along a particular line in the visual field.
BANDAGE CONTACT LENS – Clear contact lens material, such as an ACUVUE lens, without corrective power used to protect and heal the eye after an abrasion or surgery.
CANDIDACY – A person or thing considered suitable for a particular purpose.
CATARACT – Area of opacification in the natural lens of the eye (which is located behind the colored iris) that occurs as a natural consequence of aging, and impedes the transmission of light rays to the retina.
CORNEA – The clear, dome-shaped surface that covers the front of the eye, and that is responsible for most of the focusing power.
CORNEAL ABRASION - Scratch on the front surface of the eye.
DIAGNOSTIC – A test which indicates the presence of a particular state or characteristic.
DIOPTER – Measure of the focusing power of a lens, defined as the reciprocal of the focal length measured in meters.
EPITHELIUM – The outermost layer of cells of the cornea and is the eye's first defense against infection.
FORNIX – Inter-related to cul-de-sac. It is the area in the eye where the inner eyelid meets the white part of the eyeball and can be seen by pulling the lower eyelid down.
HYPEROPIA – Farsightedness: visual defect in which the eye focuses rays of light so that the focal point is behind the retina. The hyperopic eye is not able to see objects that are nearby.
INFILTRATES – Small whitish cloudy particles that appear in the cornea that is normally free of such particles.
LASIK – Stands for LASer In situ Keratomileusis. A microkeratome is used to remove an outer layer of corneal tissue, a laser is used to reshape the exposed corneal tissue, and then the outer layer of corneal tissue is replaced.
MICROKERATOME – The microkeratome is the instrument that creates the corneal flap during LASIK surgery.
MYOPIA – Nearsightedness: refractive error in which the eye focuses rays of light so that the focal point is in front of the retina, with the result that the eye is not able to see objects that are far away.
PRESBYOPIA – Naturally occurring process of aging, whereby changes in ocular tissues result in loss of accommodation in near vision, usually occurring soon after 40 years of age.
PRESCRIPTION – Applies to written instructions for an optician on the lenses for a given person to correct their refractive error.
PRK – Stands for PhotoRefractive Keratectomy. PRK involves the application of the excimer laser to remove corneal tissue in order to change the surface curvature of the eye and thus correct refractive error.
PTK – Stands for PhotoTherapeutic Keratectomy. PTK involves laser removal of the epithelium by ablating microscopically thin layers and etching away surface irregularities. Candidates for PTK are patients with significant visual compromise due to corneal scars and opacities, corneal dystrophies, and recurrent corneal erosions (RCE) that are unresponsive to initial medical treatments.
REFRACTIVE ERROR – Condition where light entering the eye is not clearly focused on the retina, resulting in blurred vision.
STRABISMUS – Misalignment of the visual axes of the eyes that impairs binocular vision
TOPOGRAPHY – The technique of graphically representing the exact physical features of a place or region, such as the cornea, on a map.