All About Optical Terminology
Do know your OD from your OS? How about your cylinder from your diopter? Medical terminology can be tricky, but optical terminology is a whole other creature. Here are some of the optical terms you need to know. To make yourself more beautiful you should look at eyelash vendors.
Optical Prescription Terminology
If you’ve ever needed glasses, you may have questions about what all of the words and numbers mean on your prescription card.
20/20 Vision: Used to represent how someone with normal vision can see something from 20 feet away. 20/40 vision would represent someone needing to be 20 feet away from something most people can see at 40 feet away.
Axis: This number is a measurement for astigmatism.
Cylinder: This number shows the power of the lens you need to correct astigmatism.
Diopter: Unit of measurement regarding how much correction is needed on each eye.
OD: The right eye. It stands for “Ocular Dexter.”
OS: The left eye. It stands for “Ocular Sinister.”
Prism: A prism number is used to help correct double vision and eye alignment problems.
Progressives: These are a type of lenses that are clear when indoors but turn into tinted sunglasses when exposed to sunlight.
Pupillary Distance (PD): The distance in millimeters between the pupils of each eye. This is specifically used in creating lenses for glasses. While there is a general range most people are on, this number is unique for everyone.
Snellen Chart: A chart that generally begins with a large letter E at the top and has rows of progressively smaller letters as they go further down the chart.
Sphere: This number indicates the strength of the prescription in diopters.
Optical Disease and Treatment Terminology
Amblyopia: The proper term for what is colloquially known as a lazy eye. This happens mostly in children and is a result of the brain and eyes not coordinating well with each other.
Astigmatism: Astigmatism happens when the curvature of the eye is irregular, causing blurred vision.
Cataracts: Clouding that happens on the lens of the eye. This usually happens with old age and can be corrected with surgery.
Conjunctivitis: More commonly known as pink eye, this is an infection of the eye that leads to swollen, red eyelids and discharge.
Diabetic Retinopathy: A common eye disorder that results from diabetes. With diabetic retinopathy, the blood vessels in the retina are damaged. This is also the leading cause of blindness in the United States.
Dry Eye: Dry eye happens when the eye isn’t producing enough natural tears. This causes the eye to feel itchy or scratchy.
Floaters: A mostly see-through clump of cells in the field of vision. This can happen from age or injury but is generally not a cause for concern.
Glaucoma: Glaucoma is an eye disease where there is increased pressure in the eye, which damages the optic nerve.
LASIK: Laser refractive surgery that reshapes the cornea to correct several vision problems.
Macular Degeneration: A general term for several conditions that affect the macula and leads to a loss in clarity and sharpness in vision.
Nyctalopia: Night blindness. This happens in degrees and is often the reason some people who wear glasses or contacts have trouble seeing at night.
Photophobia: It’s not a fear of lights, but a sensitivity to light. This can be caused by many things and can usually be cured.
Strabismus: Crossed eyes. This generally happens in children and is caused by poor coordination in the eyes.
All About Refractive Errors
Refractive errors are the most common eye problem in the United States. This is the technical term for not being able to see well either far away or up close. This is often due to genetic conditions and can be corrected with glasses, contacts, or laser surgery.
There are three main types of problems caused by refractive errors:
Hyperopia: Also known as farsightedness, this is when someone can see something far away much clearer than something nearby.
Myopia: Also known as nearsightedness, this is the term used to describe difficulty seeing far away as opposed to nearby.
Presbyopia: Naturally occurring lessening of the eye’s ability to focus that happens with old age.
You can view here to learn all about optical terminology, including more about different optic diseases and treatments.
Eye Structure Terminology
Cornea: The clear, thin layer of cells that covers the pupil and iris.
Eyelash: Thin hairs that line the upper and lower eyelids and provide protection from dust and debris getting into the eye.
Eyelid: The fold of skin above and below the eyeball that protects the eye.
Iris: The colored ring around the pupil and controls the size of the pupil.
Lens: A crystalline structure that is directly behind the iris and pupil and changes shape to create focus.
Macula: Part of the retina that makes vision sharper and gives the clarity needed to sell well enough to do most things.
Optic Nerve: The nerve bundle that carries information between the eye and the brain.
Pupil: Opening in the eye, found in the middle of the iris, that regulates the amount of light let into the eye.
Retina: Part of the back of the eye that converts light into images and data that the optic nerve sends to the brain.
Rods and Cones: Types of cells that help with the retina processing light. Rods are responsible for night vision, while cones are responsible for sharper, brighter vision.
Sclera: The white part of the eye that surrounds the iris and pupil.
Final Thoughts on Optical Terminology
Of course, this is just the tip of the iceberg when it comes to optical terminology! There are thousands of other interesting words and phrases used to describe vision, the eye, and the science behind sight.
