Add - The power added to the distance prescription to provide for near vision

Anti-reflective coating - a clear thin film of a certain thickness that when applied to a lens will absorb light that would have been reflected.

Anti-scratch coating - a clear tough coating applied to plastic lenses to reduces scratches.

Astigmatism - a condition of the eye where the meridians of the eye are not the same causing a spot of light to appear as a streak

Axis - the visual system of the eye has been broken down into 360 degrees like the numbers on a clock. These degrees are called axis and are used when prescribing astigmatism where the axis do not contain the same power.

Base - the thickest part of a prism and used to indicate the location of the prism when part of the prescription.

Base Curve - the curve on the back side of a lens. In glasses it allows for clearance of the lashed when blinking, and in contact lenses it has an effect on the fit of the lens on the eye.

Bridge size - the distance between eyeglass lenses to provide room for the nose.

Cataracts - a clouding of the intraocular lens used to change focus.

Computer Vision Syndrome (CVS) - A group of eye and vision problems experienced during computer use. Symptoms include eye fatigue, burning/irritated eyes, double and/or blurred vision, as well as, back, shoulder and neck pain.

Convergence - the process of turning the eyes inward to fixate on a nearby object.

Cylinder - the difference between the greater and lesser power of the major meridians of the eye in astigmatism.

Diopter - a measure of the refractive power of a lens as relates to a meter of distance.

Eye size - The horizontal measurement of a lens in millimeters.

Hyperopia - otherwise known as farsightedness where the focuses beyond infinity when at rest

Infra-red - that part of the energy spectrum between 760 and 3000 nm. known as the heat ray and outside the visual spectrum.

Lens coatings - surface coatings placed on a lens that filters the light going through it.

Mirror coating - known as flash coating which is applied to the front surface of the lens to give a mirror effect.

Myopia - otherwise known as nearsightedness where the eye focuses inside of infinity when at rest.

Nose pad - that portion of the eyeglass that rests on the nose.

Ocular - having to do with the eye and vision.

OD - short for oculus dextrous which is latin for right eye.

OS - short for oculus sinister which is latin for left eye.

Photochromic - a type of lens which gets dark when exposed to light.

Polarized - light that vibrates in only one meridian such as reflected glare, instead of all meridians such as found with normal light.

Presbyopia - a condition where the eye looses it's ability to change focus from distance to near.

Prism - a lens where one edge is thicker than the opposit edge.

Pupillary distance - the distance between the visual axis of the two eyes.

Sphere - the difference between the base curve of the front and back curve of the lens.

Temple length - the distance from the hindge of the glasses to the top of the ear in inches.

Ultraviolet - that part of the energy spectrum between 200 and 380 nm. and outside the visual spectrum.

Viewing distance - the distance between a computer screen and the eye which is generally 20 to 28 inches.

Visible spectrum - that part of the energy spectrum between 380 and 760 nm visible to humans.

End of Optical Glossary