Modification & Delivery
Glossary

 

A

annular bifocal contact: a lens with distance portion ground into the center of the lens and the near portion ground into the periphery.

aphakic lenses: lenses designed for post-catsaract fitting.

apical zone of cornea:the central portion of the cornea with a constant radius of curvature. Also called the corneal cap.

artificial tears: wetting agents for the cornea to supplement the loss of tear formation.

aspheric lens: a lens which is not spherical in shape. The curvature gradually flattens as the periphery is approached.

B

bactericide: a chemical that disinfects and kills pathogenic organisms.

benzalkonium chloride: a preservative used in contact lens solutions because of its germicidal qualities.

biomicroscopy: a method of examining the cornea under a magnification of from 10 to 50 times utilizing a slit lamp.

bullous keratopathy: total swelling of the cornea with painful blister formation at the epithelial level; treated frequently with a therapeutic soft lens.

Burton lamp: an ultraviolet light used to illuminate the fluorescein dye that is used to analyze the fit of a rigid contact lens.

C

chord length: the straight-line measurement of the contact lens diameter from edge to edge.

circumcorneal injection: redness around the limbus surrounding the cornea.

contact lens wetting angle: the angle between the liquid and the lens surface.

contour lens: a tricurve lens designed to conform to the curvature of the cornea, which flattens as it extends in the periphery.

copolymer: two or more chemicals that are combined to form a new chemical compound.

corneal cap: the apical zone or central zone of the cornea that has a constant area of curvature.

corneal diameter: the diameter of the cornea, usually taken along the horizontal meridian with a ruler. Also called visible iris diameter.

corneal edema: swelling of the cornea caused by hypoxia or insufficient oxygen.

D

deturgence, corneal: the state of relative dehydration maintained by the normal intact cornea that enables it to remain transparent.

diagnostic fitting set: a set of trial lenses used to gain an overview of the fit of a contact lens.

disinfection: physical or chemical procedures that kill common pathogenic organisms but may permit some nonpathogenic organisms to survive.

DK value: a measure of the oxygen permeability through a given material where D is the diffusion coefficient for oxygen movement in the lens material and K is the solubility of oxygen in this material.

double slab-off lenses: sometimes called thick-thin lenses; the upper and lower portions of the lens are reduced in thickness so that when the lens is placed on the eye these portions lie under the upper and lower eyelids. The thin zones aid in stabilizing toric soft lenses.

dry spots: areas of drying as noted by absent areas of fluorescein-stained tear film on the cornea when the patient stares.

Dyer nomogram: system of lens ordering: a simplified system of ordering rigid lenses based on clinical experience, corneal topogometry, and charts of associated lens parameters.

E

endophthalmitis: an inflammation of the entire eye including the outer coats.

enzyme cleaner: a cleaning agent that acts on a soft lens by a digestion of protein.

epithelial edema: edema of the superficial layer of the cornea.

esthesiometer (Cochet-Bonnet a device used to evaluate corneal sensitivity, consisting essentially of a nylon thread mounted in a handle so that its length may be varied and calibrated in milligrams of weight necessary to bend a given length of the thread when pressed against the cornea.

eversion of the eyelid: the folding back of the eyelid on itself.

F

finished lens: a complete lens with anterior and posterior curves, a specified diameter, a designated peripheral curve, and edge design.

fitting set: a complete inventory of lenses of graduated powers and base curves.

flare: flutterings or fringing of lights caused by a lens with an optic zone too small as a decentered lens or an excessively loose lens.

flat cornea: a cornea with a K value less than 41.00 D.

fluid lens: power created by having a very convex or concave tear film.

fluorescein: an organic compound that is inert and used to stain the tear film for contact lens fitting and to assess the integrity of the cornea.

G

giant papillary conjunctivitis (GPC): large elevated papules in the tarsal conjunctiva. Usually associated with soft lens wear.

H

haptic: the part of a contact or intraocular lens that supports the optic portion and touches the peripheral or nonoptic portion of the cornea: the word indicates �fastening, contact, sense of touch.�

hydrogen peroxide: a bactericide used for soft lenses.

hypoxia: low in oxygen

K

keratitis: inflammation of the cornea

keratoconjunctivitis sicca: drying of the cornea and conjunctiva.

keratoplasty: a corneal transplant

L

LD +2: the longest diameter (LD) of the optic zone plus 2 mm (for the intermediate and peripheral curves) yields the diameter of a lens; determined by use of the topogometer.

lenticular lens: relatively large lens most suitable for large, flat eyes; consists of a central optic zone and a surrounding nonoptic flange.

limbal zone: junction between the periphery of the cornea with the sclera.

loose lens: a contact lens with excessive movement; it can be caused by a lens that is too small in diameter, too thick or too flat.

M

microthin lens:a lens less that 0.10 mm in thickness.

minus carrier:a lens designed with an edge configuration similar to that of a minus lens that is thicker at its periphery; often used with high-plus lenses such as aphakic lenses

monovision: single-vision contact lenses used for presbyopes for whom the power of the lenses is such that one eye is used for distance vision and the other is used for near vision.

N

nomogram:a table of precalculated mathematical values used to arrive at the specifications of a rigid lens design.

O

orthokeratology: the technique of flattening the cornea and thus correcting refractive errors by the use of a series of progressively flatter contact lenses.

overwearing syndrome: a misnomer for acute corneal hypoxia characterized by a latent interval after removal of the lens; extreme pain and congestion of lids, cornea, and conjunctiva are experienced. It is more common with rigid lenses.

oxygen flux: a measure of the amount of oxygen that will pass through a given area of material in a given unit of time.

oxygen permeability: the degree to which a lens permits the passage of oxygen across it. It depends on the composition of the plastic (that is, silicone has excellent permeability, whereas PMMA has no permeability), the thickness of the lens, and its water content. It is often expressed as the DK value.

P

pachometer: an instrument used to measure the thickness of the cornea and depth of the anterior chamber.

photokeratoscope: an instrument designed to photograph annular rings of the cornea and to aid in making a contact lens that will contour to the cornea. photophobia: sensitivity to light

Placido�s disc: a disc with concentric rings to determine the regularity of the cornea when its reflection is revealed on the corneal surface.

plano lens: a lens with zero power.

polymer: a chain of linked molecular unity of dimension greater than 5 monomer unity.

polymerization: the union of molecules of a compound to form larger molecules and a new compound.

polyvinyl alcohol: a wetting agent.

prism ballast lens: contact lens with base-down prism added inferiorly to improve the stability of the lens. Usually 1 to 1.5 D of prism is added.

R

radial keratotomy: a surgical procedure in which clocklike incisions are made into the cornea to flatten the cornea and correct myopic refractive errors.

residual astigmatism: the astigmatism present after the corneal astigmatism has been nullified by a contact lens.

retroillumination: light is focused on deeper structures such as the iris, while the microscope is adjusted to study the cornea.

S

Schirmer test: measures normal tear secretion; the ability of the eye to wet in 5 minutes 15 mm of a 5 x 35 mm strip of filter paper.

semifinished blank: a contact lens blank in which the posterior curve of the contact lens has been fabricated.

soaking solution: a solution designed to keep a lens moist and free from contamination.

Soper lens: a rigid lens designed by Joseph Soper with a steep central posterior curve to accommodate large cones of keratoconus.

spectacle blur: blurred vision that lasts for 30 minutes or longer after a rigid lens is removed and spectacles are employed.

specular reflection: a reflection from a mirror surface, such as the back of the cornea.

spheric equivalent: It is the spheric power of the lens plus half the cylindric power.

sterilization: a method to ensure the complete death of all forms of bacteria fungi, and spores.

stippling: dotlike staining of the cornea

superficial punctate keratitis (SPK): diffuse stippling of the cornea.

surfactant: a cleanser that acts on the surface of a contact lens

. T

tear film breakup time (BUT): an evaluation of tear quality; the tear film will normally break up in 10 to 30 seconds and show dry sports. Any dry spot that appears in less than 10 seconds is pathologic.

thermal disinfection: disinfection of a lens by heat

thickness of a lens: the measurement of the center of a lens

thimerosol (Merthiolate): a mercurial agent used for disinfection.

three and nine o�clock staining: erosion of the cornea at the 3 and 9 o�clock position; seen usually in patients wearing rigid lenses;

three-point touch: that area of the cornea between the apical zone and the limbal zone.

truncation: a design feature used in toric lenses to reduce lens rotation by cutting off a peripheral portion of the lens to conform with the lower lid border.

U

ulceration of the cornea: a large defect in the cornea which may be caused by hypoxia, trauma, or infection.

V

V-groove gauge: a ruler measure with a groove to measure the diameter of a rigid lens.

vascularization: increased blood vessels occurring in a cornea.

visible iris diameter (VID): a term that represents the iris diameter and aids in selecting the initial lens; often used in place of the corneal diameter.

W

warpage: a permanent bending of a rigid lens. May also refer to a semipermanent altering of the corneal curvature.

wet storage: the use of soaking solution to store rigid contact lenses.

wetting solution: solutions that increase the spreading or wettability of liquids in the plastic contact lens by converting the surface of a lens from a hydrophobic to a hydrophilic surface.