The Eye
This clear, dome-shaped outer layer of the eye provides about two-thirds of the eye’s total refractive power.
What is the cornea?
A minus sign (-) preceding the sphere power in an eyeglass prescription indicates this vision condition.
What is myopia (or nearsightedness)?
These multifocal lenses feature a distinct visible line separating the distance power from the near power.
What are bifocals?
Abbreviated AR, this lens treatment reduces surface reflections and glare to improve vision and visual appearance.
What is an anti-reflective coating?
This term describes the bending of light waves as they pass from one medium to another.
What is refraction?
The colored part of the eye that controls how big or small the pupil gets.
What is the iris?
This abbreviation on a prescription refers to the left eye.
What is OS?
These no-line multifocal lenses provide a smooth transition between distance, intermediate, and near viewing zones.
What are progressives (or PALs)?
This type of lens treatment repels water drops, preventing moisture from pooling on the surface.
What is a water-resistant (or hydrophobic) coating?
The primary source of natural light and natural UV radiation on Earth.
What is the Sun?
The dark opening in the center of the eye that changes size to let light in.
What is the pupil?
Measured in degrees from 1 to 180, this value indicates the orientation of the astigmatism correction.
What is the axis?
Known for high impact resistance and lightweight properties, this lens material with an index of 1.59 is the standard for safety, rimless, and youth glasses.
What is polycarbonate?
This lens treatment is designed to repel oils, fingerprint smudges, and facial grease.
What is an oil-resistant (or oleophobic) coating?
The narrow portion of the electromagnetic spectrum that the human eye can actually see.
What is visible light?
The light-sensitive layer at the back of the eye that acts like a camera sensor.
What is the retina?
This measurement, abbreviated PD, ensures accurate optical alignment with the eyes.
What is pupillary distance?
Lenses designed with one prescription across the entire lens.
What are single vision lenses?
A protective surface coating applied to all Zenni lenses.
What is a scratch-resistant or anti-scratch coating?
Invisible radiation just past the violet end of visible light that can cause sunburns and ocular damage.
What is Ultraviolet (UV) radiation (or UV light)?
Carries visual signals from the back of the eye straight to the brain.
What is the optic nerve?
To transpose a prescription from plus-cylinder format to minus-cylinder format, you change the axis by this many degrees.
What is 90 degrees?
Thinner and lighter lenses designed for strong prescriptions.
What are high-index lenses?
A lens treatment designed to block harmful rays from the sun that can damage eye health over time.
What is UV (ultraviolet) protection?
The metric unit used to measure light wavelengths across the spectrum.
What is a nanometer (nm)?