A • B • C • D • E • F • G • H • I • J • K • L • M • N • O • P • Q • R • S • T • U • V • W • X • Y • Z
A
Aberration:
Distortions, related to astigmatism, that cause the inability of light rays entering the eye to converge (come together) to a single focus point on the retina. Aberration are divided into two main categories: higher-order and lower-order.
Accommodation:
Ability of the eye to change its focus between distant objects and near objects.
Acuity:
Sharpness, acuteness, or keenness of vision.
Acute:
Occurring suddenly.
Adnexa:
Accessory structures of the eye, including the eyelids, lacrimal apparatus, etc.
Amblyopia:
Dullness or obscurity of sight for no apparent organic reason, therefore not correctable with glasses or surgery. Sometimes called a lazy eye, wherein one eye becomes dependent on the other eye to focus, usually developed in early childhood. Often associated with strabismus.
Amsler grid:
Hand held chart featuring horizontal and vertical lines, usually white on black background, used to test for central visual field defects.
Anesthesia :
Medication that eliminates or reduces pain for surgical procedures. Local or regional anesthesia numbs only a certain area.
Anisometropia:
Condition of the eyes in which they have unequal refractive power.
Anterior chamber:
Space between the cornea and iris, which contains aqueous humor.
Aphakia:
Absence of the lens of the eye.
Aqueous humor:
Transparent fluid occupying the anterior chamber and maintains eye pressure.
Aspheric optic :
A type of lens designed to compensate for spherical aberration, resulting in improved image quality.
Astigmatism:
Structural defects of the eye in which the light rays from a viewed object do not meet in a single focal point, resulting in blurred images being sent to the brain. An astigmatic cornea is not perfectly rounded like a basketball but has an irregular shape more like the side of a football. Astigmatism is most often combined with myopia or hyperopia.
Axis:
Optical - a straight line through the centers of both surfaces of a lens. Visual - a straight line from the object of vision to the fovea of the eye.
B
BCVA:
Best corrected visual acuity.
Best corrected visual acuity (BCVA):
Best possible vision a person can achieve with corrective lenses, measured in terms of Snellen lines on an eye chart.
Bifocals:
Lenses containing two focal lengths, usually arranged with the focus for distance above and near focus below.
Binocular vision:
Simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and parallax-induced depth perception.
C
Cataract:
Gradual clouding of the crystalline lens resulting in reduced vision or eventual blindness, correctable by cataract surgery.
Cataract surgery:
Removal of a cataract, replacing it with an intraocular lens implant.
Clear Lens Extraction (CLE):
Procedure in which the eye's natural clear crystalline lens is removed and replaced with an intraocular lens implant, using the same technique as cataract surgery.
Contact lens:
Small, thin removable plastic lens worn directly on the front of the eyeballs, usually used instead of ordinary eyeglasses for correction or protection of vision.
Contrast sensitivity :
The ability of the eye to differentiate between an object and its background.
Cornea:
Transparent tissue that forms the front part of the eyeball, covering the iris and pupil. The cornea is the first part of the eye that bends (or refract s) the light and provides most of the focusing power.
Corneal curvature:
Shape of the front of the eye.
Corneal relaxing incisions (CRIs):
True corneal incisions, such as RK and AK.
Corneal transplant (penetrating keratoplasty):
Surgical operation of grafting a replacement cornea onto an eye.
Crystalline lens:
Double convex, transparent part of the eye, located behind the iris and in front of the vitreous body. Serves in conjunction with the cornea to refract incoming rays of light onto the retina.
Cylinder:
Refers to the degree of astigmatism (uneven roundness) present in the cornea.
D
Depth perception:
Ability of the vision system to perceive the relative positions of objects in the visual field.
Diffraction :
The spreading of light that occurs when light passes through discontinuities (i.e., the steps or edges of a lens). In an optical system, light can be diffracted to form multiple focal points or images.
Diopter:
Unit of measure of the refractive power of an optical lens (equal to the power of a lens with a focal distance of one meter). A negative diopter value (such as -3D) signifies an eye with myopia and positive diopter value (such as +3D) signifies an eye with hyperopia .
Distance vision:
The range of vision that includes focal points 7 feet or further from your eyes. Items that typically fall within this range include billboards, street signs and movie screens.
E
Extracapsular cataract surgery:
Surgery in which the cataract is removed in one piece through a larger incision, which usually requires several stitches.
F
Field of vision:
Entire area which can be seen without shifting the gaze.
G
Glare:
Scatter from bright light that decreases vision.
H
Halos:
Rings around lights due to optical imperfections in, or in front of, the eye.
Haptics:
The arms of an intraocular lens, which holds it in place once inserted inside the eye.
I
Intermediate vision :
The range of vision that includes focal points between 16 inches and 7 feet away from your eyes. Items that typically fall within this range include computer screens and car dashboards.
Intraocular lens implant (IOL):
Permanent, artificial lens surgically inserted inside the eye to replace the crystalline lens following cataract surgery or clear lens extraction.
Intraocular pressure (IOP):
Fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber.
Iris:
Colored part of the eye. Elastic, pigmented, muscular tissue in front of the crystalline lens that regulates the amount of light that enters the eye by adjusting the size of the pupil in the center.
L
Laser:
Device that generates an intense and highly concentrated beam of light. Acronym for: Light Amplification by Simulated Emission of Radiation. (Also see: holmium laser, argon laser, Nd: YAG laser, femtosecond laser, and excimer laser)
Lens:
Same as the crystalline lens. Double convex, clear part of the eye, behind the iris and in front of the vitreous humor. Serves to refract the various rays of light so as to form an image on the retina.
Lens optic :
The round central portion of the IOL that serves as the corrective lens.
Limbal relaxing incisions (LRI):
Small incisions placed on the far peripheral aspect of the cornea resulting in a cornea that is more round, for correcting astigmatism.
M
Monofocal IOL :
An intraocular lens that provides patients with only one focal point. Typically, these lenses only correct distance vision.
Monovision:
Purposeful adjustment of one eye for near vision and the other eye for distance vision.
Multifocal IOL :
An intraocular lens that provides patients with multiple focal points, correcting vision at a range of distances.
Myopia:
Also called nearsightedness or shortsightedness, the inability to see distant objects as clearly as near objects.
N
Near vision :
The range of vision that includes focal points 16 inches or closer to your eyes. Items that typically fall within this range include books, newspapers and medicine bottles. Also known as "reading vision."
Normal vision:
Occurs when light is focused directly on the retina rather than in front or behind it.
O
OD:
Abbreviation standing for "oculus dextrum" meaning: right eye.
Ophthalmologist:
An ophthalmologist is either a medical doctor (MD) or an osteopathic physician (D.O.) who is qualified and especially trained to diagnose and treat all eye and visual system problems, both medically and surgically, as well as diagnose general diseases of the body.
OS:
Abbreviation standing for "oculus sinistrum" meaning: left eye
Overcorrection:
Occurence in refract ive surgery where the achieved amount of correction is more than desired; in LASIK, typically due to a patent's over-response to the laser ablation.
P
Peripheral vision:
Ability to perceive the presence, motion, or color of objects outside the direct line of vision.
Personal Best Vision:
Best possible vision for each individual as corrected.
Phacoemulsification cataract surgery:
Cataract removal procedure which involves making a tiny incision, about 1/8" long. A pen-like instrument, inserted through the opening, is used to emulsify and aspirate the clouded lens material, using gentle sound waves. Then an intraocular lens is inserted into place.
Phacofracture cataract surgery:
Cataract surgery in which the lens is removed through a small incision by "fracturing" it into several small segments, rarely used today.
Phakic Intraocular Lenses (IOLs):
Placed inside the eye without removing the natural lens, and performs much like an internal contact lens.
Posterior capsule:
The thin membrane in the eye that holds the crystalline lens in place.
Presbyopia:
Inability to maintain a clear image (focus) as objects are moved closer. Presbyopia is due to reduced elasticity of the lens with increasing age.
Pupil:
Black circular opening in the center of iris through which light passes into the crystalline lens . It changes size in response to how much light is being received by the eye, larger in dim lighting conditions and smaller in brighter lighting conditions.
R
Refract:
To bend aside, as in "the crystalline lens refract s the light as it passes through", or to measure the degree the eyes or lenses bend light, as in "the doctor refract s a patient's eyes".
Refraction:
Test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.
Refractive power:
Ability of an object, such as the eye, to bend light as light passes through it.
Refractive surgery:
Type of surgery (such as LASIK) that affects the refract ion of vision.
Retina:
Layer of fine sensory tissue that lines the inside wall of the eye, composed of light sensitive cells known as rods and cones. Acts like the film in a camera to capture images, transforms the images into electrical signals, and sends the signals to the brain by way of the optic nerve.
Routine eye exam:
To test the overall condition of the eye and prescribe corrective measures such as glasses, contact lenses or LASIK.
S
Sclera:
White part of the eye. Tough covering that (with the cornea) forms the external, protective coat of the eye.
Snellen eye chart:
Most common chart used to test visual acuity with black letters of various sizes against a white background.
Snellen optotypes:
Specifically formed letters of the alphabet arranged in rows of decreasing letter size on the Snellen chart.
Sphere:
Focusing power of the corrective lens.
Spherical aberration :
An irregularity in the shape of the lens. As the eye ages, the lens gets thicker and rounder, causing image quality to deteriorate. Often associated with loss of contrast sensitivity and poor night vision.
Stereoscopic vision:
Ability to see in three-dimension.
T
Topography:
A tool used to see the refractive problems that might be present in the cornea. Corneal topography is used not only for screening all patients before refractive surgery like LASIK but also for fitting contacts.
Toric:
Lens (eyeglasses, intraocular lens, or contact lens) that is the warped (astigmatic) opposite to that of the eye, thereby canceling out the error.
Trifocals:
Lenses containing three focal lengths, usually arranged with the focus for distance above, intermediate distance in the middle, and near vision below.
U
UCVA:
Uncorrected visual acuity.
Uncorrected visual acuity (UCVA):
Best possible vision a person can achieve without corrective lenses measured in terms of Snellen lines on an eye chart.
V
Vision:
The ability of the brain to see and interpret what is in front of the eyes.
Vision therapy:
Orthoptics, vision training, eye exercises. Treatment process for the improvement of visual perception and/or coordination of the two eyes, for more efficient and comfortable binocular vision.
Visual acuity:
Clearness of vision; the ability to distinguish details and shapes, which depends upon the sharpness of the retina l image.
W
Wavefront:
Wavefront technology produces a detailed map of the eye. The information is transferred to the laser via computer software.
Y
YAG laser surgery:
Properly called Nd:Yag laser capsulotomy, a procedure using a Nd:YAG (neodymium-yttrium-aluminum-garnet) laser, used primarily to treat secondary cataract s (capsular haze) that occur subsequent to the primary cataract procedure, or to relieve increased pressure within the eye from acute angle-closure glaucoma via a peripheral iridotomy. It can also be used to treat open angle glaucoma in a procedure called selective laser trabeculoplasty.
