Contact Lens Manual Chapter 1 Terms

Corneal Abrasion

Scraped area of corneal surface accompanied by loss of superficial tissue (epithelium)

Accomodation

The ability of the crystalline lens to adjust power to provide retinal focus of images of objects closer than optical infinity

Add

Additional amount of plus power required for focusing at near

Amblyopia

Loss of vision without any apparent disease of the eye

Ametropia

A refractive error in which the eye, when in a state of rest, does not focus the image of an object upon the retina; includes hyperopia, myopia, and astigmatism

Aphakia

Absence of the crystalline lens

Apical, apex

The extreme top or tip of a curve, ex: corneal apex

Apical bearing, apical touch

The posterior lens curvature resting on the corneal apex to achieve optimal lens positioning.

Aqueous humor

Clear, watery fluid that fills the space between the back of the corneal surface and the front vitreous surface, bathing the crystalline lens. Produced by the ciliary processes, it nourishes the cornea, iris, and lens and maintains intraocular pressure

Aqueous tears

The watery component of the tears

Arcuate stain

An arc shaped corneal abrasion caused by the edge of a contact lens

Aspheric

Not spherical. A posterior or anterior lens surface design which flattens at a given rate (eccentricity) as the curve progresses toward the periphery

Astigmatism

A refractive defect where the refractive surface has a different power in different meridians. As a result, the image formed of a point object will not be a point, but a line

Axial edge lift

Vertical distance from the lens edge to an extension of the base curve of a lens

Cylinder axis

The weakest, or least curved, meridian on the surface of a cylinder or toric surface

Principal axis

An imaginary line going through the geometric center of an optical system, perpendicular to the surface

Back toric

A lens design with two principal curves at right angles to each other on the lens posterior

Bandage lens

Soft contact lens used for protecting damaged or irregular corneal surfaces

Base curve

Of a contact lens, the curvature of the posterior optical portion, otherwise known as the Central Posterior Curve (C.P.C.)

Bell’s phenomenon

Upward and outward deviation of the eyes occurring in sleep or with forcible closure of the eyelids

Bicurve lens

A lens consisting of two posterior curvatures; one central curve (base curve) and one peripheral curve

Binocular

Referring to or affecting both eyes

Bitoric

A lens design with two principal curves at right angles to each other on both the anterior and posterior lens surfaces

Blends

The junctures between posterior curves after being smoothed out by poishing

Blepharitis

Inflammation of the eyelids, usually with redness, swelling, and itching

Blepharoplasty

Any plastic surgery of the eyelids, ex removal of excessive lid skin or sub cutaneous fat

Bullous keratopathy

Degenerative process characterized by small blister-like pockets that form in swollen corneal epithelial layers; markedly reduces vision

Break-up time (BUT)

Measurement of the time interval between a blink and the development of a dry spot in the pre-corneal tear film; less than 10 seconds is abnormal

CAB (cellulose acetate butyrate)

A first generation, low Dk (4.0 Dk) gas permeable lens material

Cataract

A condition in which the crystalline lens of the eye, or its capsule, or both, become opaque with consequent loss of visual acuity

Chalazion (internal hordeolum)

Inflammatory enlargement of a meibomian gland of the eyelid

Chord length

The measurement of a straight line joining the ends of an arc

CN bevel/anterior bevel

Angulation placed on the anterior (front) surface of a lens to reduce edge thickness and decrease lid sensation

Conjunctiva

Mucous membrane that lines the eyelids and covers the front part of the eyeball

Copolymer

A polymer containing two or more different monomer units

Cornea

Clear, transparent portion of the outer coat of the eyeball; the “window” of the eye

Corneal dystrophy

Abnormal or defective development of the cornea; degeneration of the cornea

Corneal graft (transplant)

Operation to restore vision by replacing a section of opaque cornea with a clear section from a donor

Cylinder

An object whose surface is curved differently in different meridians with the axis having zero curvature

Cylinder lens

A lens with a different power in different meridians due to one or more surfaces having cylinder or toric shape

Cylinder power

The algebraic difference in power between the principal meridians of a cylinder lens

Daily wear lens

A contact lens designed to be worn for less than 24 hours, with cleaning and disinfection performed between wearing periods

Dellen

Localized zone of corneal thinning, usually at the limbus, caused by excessive dehydration

Dessication

Drying of the cornea usually due to improper wetting of the horizontal corneal extremes

Dimple veiling

Indentations in the corneal epithelium caused by air bubbles getting between the back of the lens and front of the cornea. Detected with fluorescein stain

Diopter

A unit of measurement equal to a reciprocal meter, used to measure vergence of light and power of optical lenses D

Dispersion

The separation of white light into its spectral colors

Diuretic

Substance that increases the amount of urine excreted

Dk

Refers to the inherent permeability of a lens material to allow the passage of gases through it

Dk/t

Refers to the amount of oxygen (gases) which pass through a lens material of specified thickness

Duo-chrome test

Method of refining a refraction by comparing relative clarity of equal-size objects seen on red, then on green, background

Corneal edema

Swelling of the cornea, which in turn causes a loss of clarity

Eccentricity

The rate or amount of flattening of an aspheric curve. Measured as “e” valuee

Effectivity

Changes in the vergence of light between one point and another. In contact lens practice this change is most often observed when the position of the correcting lens is moved from the spectacle place to the corneal plane

EOP

Equivalent oxygen percentage

Recurrent corneal erosion

Episodic loss of corneal epithelium due to its failure to adhere properly to Bowman’s layer. May follow minor scratch-type injury

Extended wear lens

A contact designed to be worn 24 hours per day, for up to sever continuous days

Fenestration

A tiny hole in a contact lens, made to enhance the transmission of tears and oxygen through the lens material

Aqueous flare

Tyndall effect, or the scattering of light, in a beam directed into the anterior chamber. This scattering is a result of increased protein content of the aqueous humor, which is a sign of sever inflammation of the iris and/or ciliary body

Flexible wear lens

A contact lens designed for occasional overnight wear

Fluorescein dye disappearance test

Evaluates tear drainage system; dye dropped onto conjunctiva of an eye with normal drainage should disappear within 5 minutes

Fluorescein pattern

The appearance of the tear film distribution between the posterior of a rigid lens and the anterior corneal curvature as viewed with fluorescent dye

Sodium fluorescein

Fluorescent dye that can be injected intravenously to study blook flow through the retina and choroid. It can also be applied directly in the palpebral fissure to detect corneal abrasions or wound leaks, or to evaluate the fit of rigid contact lenses

Focal length

The distance from the vertex of an optical source to its focal point. The reciprocal of the focal length is the dioptric power

Focal point

The point along the principal axis of an optical system where incident parallel light will be focused after being converged or diverged by that system

Fogging

A refraction refinement technique where a plus powered lens is placed before the eye to relax accommodation

Front toric

A lens design with two principal curves at right angles to each other on the lens anterior

FSA (fluoro-silicone acrylate)

A rigid gas permeable material which contains fluorine for stability, wettability, and added oxygen transmission; silicone for oxygen permeability; and methylmethacrylate for machinability and good optical quality

Giant papillary conjunctivitis (G.P.C.)

Allerguc type of conjunctival inflammation associated with soiled soft contact lenses. Hard, flat papillae form a cobblestone pattern on undersurface of the upper eyelid

GMMA (Glyceryl Methylmethacrylate)

A non-HEMA soft lens material

HEMA (Hydroxyethylmethacrylate)

Plastic polymer used to make soft lenses

Herpes simplex virus (HSV)

Virus that recurrently infects the cornea, producing branch-like ulcers (dendritic keratitis)

Hydrogel

A polymer that absorbs and binds water into its molecular structure

Hydrophilic

Water-loving

Hyperflange

A plus lenticular carrier

Hypertinic saline

Saltwater of a higher concentration (usually about 5%) than normal saline (0.9%). Used in ointment fir dehydrating a cornea swollen with water in diseases that damage the endothelial water pump system, such as Fuch’s dystrophy

Hypesthesia

Impaired or decreased sensitivity to touch, as caused by damage to nerves supplying that region

Hypoxia

Deficiency of oxygen reaching tissues of the body

Image

An optical reproduction of an object by a lens or mirror. Real images are formed where converging light focuses, and virtual images are formed where diverging light focuses

Index of refraction

The ratio of the speed of light in a vacuum (or air) to the speed in another medium indicating the medium’s refractive ability

Optical infinity

The distance light waves must travel from a source to lose all curvature, and be essentially parallel. This distance is considered to be twenty feet

Injection (hyperemia)

Increased blood flow; usually refers to eye redness caused by congestion of conjunctival blood vessels

Intrapalpebral (fit)

A well centered rigid lens that fits between the upper and lower eyelids, where the upper lid does not control the position of the lens

Keratitis

Corneal inflammation, characterized by loss of luster and transparency

Keratoconus

Degenerative corneal disease characterized by thinning and cone shaped protrusion of central cornea

Keratometry (K reading, K’s)

Corneal curvature measurements obtained with a keratometer

Lacrimal lens

The lens that is formed by the tears that collect between the base curve of a contact lens and the anterior cornea

Lensometer

Instrument used for determining the refractive power of a spectacle or contact lens

Lens

Any piece of glass or other transparent material with ability to bend light rays in a predictable fashion

Lenticular

A lens design using a non-optical portion (carrier) in the periphery of the lens to form edges of a desired thickness

Lid attachment (fit)

A rigid lens which is tucked under the upper eyelid for better centration and comfort. The eyelid keeps the lens in position between blinks

Lift off/stand off

Pertains to a lens which is fit excessively flat, causing the edge to lift away or stand off from the cornea

Light

That portion of the electromagnetic spectrum that gives rise to the sensation of sight through stimulation of the retina

Corneal limbus

Transitional zone where the cornea joins the sclera and the bulbar conjunctiva attaches to the eyeball. About 1 to 2 mm wide

Macula latea

Literally, “yellow spot”. Small specialized central area of the retina, surrounding the fovea; responsible for acute central vision

Meibomitis

Inflammation of the meibomian glands

Microcystic edema

Advanced form of edema involving the deeper cell layers of the epithelium

Microcyst

A tiny cyst, frequently of such dimensions that a magnifying lens or microscope is required for viewing. Corneal microcysts can be caused by hypoxia

Minus lens

A lens that is thicker at edges than at center, which increases divergence of incoming light rays. Used in correcting myopia (nearsightedness)

Mires

Focusing guides on an optical instrument that aid in measurement, such as the circular targets in the keratometer