Glossary of Optical Related Terms

Also see the separate glossary for contact lenses.

Abbe Value: A numerical expression of how prone a lens material is to causing chromatic aberration. The higher the Abbe value the lower the change it will cause aberration.

Aberration: An unclear image of an object when viewed through a lens.

ABO: American Board of Opticianry an agency that provides various levels of certification for persons in the field. It is only a written exam not a practical.

Accommodation: The ability of the eye’s crystalline lens to change shape and add and reduce power to see things at different distances.

Amblyopia: Visual acuity difficulties without a specific or detectable refractive error.

Anisometropia: A substantial difference in the refractive powers of each eye.

Aphakia: A person that has had their crystalline lens removed.

Aspheric: Not spherical or not perfectly round.

Asthenopia: Eye fatigue.

Astigmatism: A misshapen cornea that causes light entering the eye to focus on many points instead of one.

Auto-refractor: A specialized instrument used to provide a doctor or tech with a base-line patient Rx.

Axis: A numeric expression of the position of the spherical portion of a prescription when it is in place in front of the eye.

Base Curve: The front curve of an ophthalmic lens. In older and now outdated surfacing it is/was the curve from which all other curves are/were measured.

Bi-Centric Grind: Another term for slab-off.

Boxing System: A way of dividing a frame into geometric shapes for measuring.

Box-O-Graph: A tool used in labs to measure lenses and frames.

Brow-Bar: The bar or bars that connect the tops of the eyewires in traditional men’s frames.

C-Sizer: A tool used to measure the circumference of a cut lens.

Caliper: The tool used to measure the thickness of a lens.

Cataract: The clouding of the crystalline lens caused by age.

Chromatic Aberration: The breaking down of white light into its component colors due to a lens material optical properties (R,O,Y,G,B,I,V)

Colmascope: (aka Polariscope) A tool use to test the stress a lens is under. It will reveal a lens that is too tight in an eyewire or a glass lens that has been properly treated for impact resistance.

Concave: Having an inward curve like the back of a modern ophthalmic lens.

Convergence: Used to describe light rays that are being directed toward each other.

Convex: Having an outward curve like the front side of a modern ophthalmic lens.

Crazed: No, not your customers! Crazing means a lens that has cracked or has a web-like pattern of splits cross the entire lens surface. Crazing is caused by chemical reaction.

Crown glass: Another term for glass, or ophthalmic glass.

Diplopia: Double vision or the seeing of a single object as two.

Divergence: Used to describe light rays that are being directed away from each other.

Double D Lens: Another term for an occupational lens.

ECP: Eye Care Professional, a generic term used by magazines for anyone in the “business.”

Edger Vomit: The mix of water and swarf that collects under a wet cut edger.

Equithin: A laboratory process used on progressives to thin the lens. The process creates prism in the lenses but the prism is balanced in such a way that it is unnoticed by the wearer.

Free-form: The creation of a lens using CAD or computer aided design and application. Both the front and back surfaces of the lens are ground in multiple planes.

Fresnel prism: A temporary stick-on prism made from a thin sheet of plastic using multiple concentric rings to create the effect of ground in prism.

Glazing: An outdated term for mounting lenses or the general process of finishing.

Groover: The lab tool that cuts the slot on the lens edge that catches the nylon cord in semi-rimless frames.

Hide-A-Bevel: A generic term for a bevel placed in the best position to hide the edge thickness of a lens.

Hydro-phobic: Water resistant. A lens coating that resists water build up, sheds rain drops and prevents fogging.

Image jump: The shift of image that an individual experiences when passing from the distance portion of a lens into the magnifying segment area in a lined bifocal.

Impact resistance: A way of expressing how much force a lens can take before breaking.

Implant: The fixed focus replacement lens that is inserted in the eye in place of the crystalline lens.

Inset: How far the reading area of a lens is moved inward nasally to match patient convergence it is equal to the far pupillary distance – the near pupillary distance.

Kera: Cornea.

Keratometer: A tool used by doctors and contact lens specialists to measure the curvature(s) of the cornea.

Laminated: A lens that is multi layered. Used in polarized lenses and in some small scale lens manufacturing processes.

Lap: The tool that holds the pads that hold the slurry that polish and fine the lenses during surfacing.

Lens Clock: A tool that reads curvature. It is capable of reading both plus and minus powers and can be used to accurately read a prescription without the use of a lensometer.

Lens Washer: (aka washer, cheater cord, liner) A thin strip of plastic used to increase the circumference of a lens that has been cut too small for an eyewire.

Lenticular: A very high-powered lens that has a central optically significant area and a thin non-optical carrier. Looks like a “fried egg.”

Major Reference Point: (MRP) The point on a lens where the patient is provided the prescription as written by the doctor. If prism is not called for in the prescription then the lens OC and the MRP are the same.

Meniscus: Term used to describe the profile of a modern lens.

Minimum Blank Size: (MBS) The smallest lens blank that can be used and still cut out to fit a frame. Eyewire size and patient pupillary distance will both effect the minimum size that can be used.

Nasal: Towards the nose. The opposite of temporal.

NCLE: National Contact Lens Examination the NCLE is a certification exam that shows a level of proficiency and understanding of the use and fitting of contact lenses. It is only a written exam not a practical.

Neutralizer: Solution in tint tanks that will bleach or neutralize the color added to a lens.

Nystagmus: Twitching eye.

OD: Right eye.

Oleo-phobic: Oil resistant. A lens coating that resists taking on facial or skin oils.

Optical axis: The point where the cornea’s focus and the fovea line up and provide best vision.

Optician: see

OS: Left eye.

OU: Both eyes.

Plano: Flat, having no power, zero, 0.00.

Polariscope: See colmascope.

Polarized: Having a filter that blocks the specific waves of light responsible for glare.

Prism Diopter: A three sided medium (prism) that will cause a ray of light passing through it to deviate from its path 1 cm at a distance 1 meter from the medium (prism).

Ptosis: Drooping eyelid.

Quadrafocal: Another term for an occupational lens.

Refraction: The bending of light as it passes through different materials.

Rolled edge: A dated technique used to grind away the thickest portions of a high-minus lens. The introduction of high-index materials made this practice almost obsolete.

Safety bevel: The smoothing out of the leading edge of a lens so it is not sharp.

Sclera: The white area of the eye.

#%&!: What you say when you stick a screwdriver into your finger.

Side shields: Plastic shields that are slipped on or riveted on safety frames.

Slit-Lamp: A bio-microscope used to see extreme detail in the surface of the eye.

Slotting File: A file intended to re-slot the shaft of a broken screw.

Smidget: A unit of measure less that a millimeter setting on an old pattern edger.

Spotting: Placing the OC and axis dots on a lens using a lensometer.

Stock Lens: A finished uncut lens that is pulled from stock, laid out for finishing and cut for a frame.

Strabismus: Eyes not looking in the same direction. A wandering eye.

Swarf: The debris left over from lens processing in surfacing and finishing.

Temporal: Towards the temple or side of the head. The opposite of nasal.

Tonometer: An instrument that measure the inter-ocular pressure of the eye.

Vertical imbalance: The shift of images created by varying powers between the two eyes. One eye perceives the object or image in one place the other eye perceives in another creating double-vision.

Zone: Another term used to describe the corridor or a progressive lens.