The Ultimate Guide to Glasses & Optical Vocabulary

When customers visit our Kerrisdale eyewear store for a new pair of glasses or contact lenses, we always make sure to explain everything and try not to swamp them with too much optical industry jargon. After all, not everyone spends their free time kicking back with the latest issue of 20/20 Magazine.

Yet, there are a lot of vision and optician terms that are worth your while to know as they can help you with everything from decoding your eyeglasses prescription to understanding different lens coatings. Or, you can just blow your friends away with your extensive glasses vocabulary. The choice is yours. Either way, here is a comprehensive optical glossary to get you started: 

The Ultimate Guide to Glasses & Optical Vocabulary

  • 20/20 Vision: This is one of the most widely used optical terms but do you know what it really means? It’s used to describe normal visual acuity (sharpness or clarity of vision) at a 20-foot distance. So, if you have 20/20 vision, you can clearly see the sign that’s 20 feet away that should normally be seen clearly from 20 feet away. 
  • Anti-Reflective Coating: This coating is applied to eyeglass lenses to reduce reflections or glare and allow more light to pass through them. Lenses with an anti-reflective coating look transparent so people can see your eyes instead of their own reflection. 
  • Astigmatism: When either the curvature of the cornea (corneal astigmatism) or the shape of the eye’s lens (lenticular astigmatism) are irregular, light rays aren’t refracted correctly creating what’s known as a refractive error. With astigmatism, vision is blurry and distorted at all distances, as opposed to just near or far.
  • Axis: If you have astigmatism, you’ll see this on your eyeglasses prescription. It shows where to place the lens correction to remedy astigmatism. It’s measured in degrees.
  • Backside Coating: Since high-index plastic lenses and polycarbonate lenses have flatter prescription curves and are much thinner, they need a hard coating on the backside of the lenses to prevent scratching. 
  • Base Curve: On an eyeglass lens, the base curve is the flatter curvature found on the front surface while on a contact lens, it’s the curve of the back surface.
  • Bifocal: This is another one of the more common glasses terms. It’s when an eyeglass lens has two parts, one for seeing things in a distance and one for seeing things up close. 
  • Bridge Size: The bridge size, or bridge width, is the distance between the lenses on a glasses frame. It’s usually measured at the widest point between the lenses.
  • Cataracts: A cataract is the clouding of the eye’s lens that results in blurry vision.
  • Cornea: The transparent, dome-shaped, outermost layer that covers the front of the eye is the cornea. It protects the eyeball from dust, debris and germs and is also important for focusing vision.
  • CR-39: This was the first lightweight, plastic eyeglass lens material to hit the market and it’s been around for nearly 60 years. It’s made from a plastic polymer known as “Columbia Resin 39” or CR-39 for short. It’s more durable than glass, is a good value, can be tinted to almost any color and has great optical qualities, which is why it’s still a popular option today.
  • Cylinder: This is the “C” on your eyeglasses prescription and it measures the degree of astigmatism you have in diopters. 
  • Diopter: This is a unit of measurement that indicates the refractive power of a lens.
  • High Index: High index lenses have a higher index of refraction so they bend light more effectively and at steeper angles than traditional eyeglass lenses. Therefore, less material and curvature is necessary to correct refractive errors aka help you see clearly. They’re thinner, flatter and more aesthetically appealing for those with higher prescriptions who would have needed extremely thick lenses in the past. 
  • Hyperopia: Hyperopia is the technical term for farsightedness. This means you can see objects more clearly at a distance but they become blurry up close.  
  • Lens Materials: This refers to what your eyeglass lenses are made of and it’s very important to choose the right lens material to meet your aesthetic, vision and lifestyle needs. Lens materials include glass (though glass is rarely used today), plastic, including CR-39 and high-index plastic lenses and polycarbonate lenses as well as other new materials such as Trivex.
  • Macular Degeneration: Macular degeneration is an eye disease that leads to vision loss. It’s caused by a deterioration of the macula. The macula is part of the retina and it’s responsible for central vision, which lets you see fine details clearly. It’s often seen in older people and referred to as age-related macular degeneration (AMD).
  • Mirrored Coating: Applied to the surface of eyeglass lenses, this coating absorbs a significant amount of light, offers glare protection and makes lenses appear darker because it has a reflective property. 
  • Myopia: Nearsightedness, or myopia, is the most prevalent refractive error of the eye. It means you can see objects clearly up close but they appear blurry at a distance.
  • Nose Pad: These are the little pads that are attached to your eyeglasses frame that sit on either side of your nose to provide comfortable support.

  • O.D. and O.S.: These are abbreviations found on glasses and contact lens prescriptions. They stand for the Latin terms oculus dexter (O.D.), which means right eye, and oculus sinister (O.S.), which means left eye. 
  • Photochromic: Photochromic lenses darken in response to sunlight but are clear when you’re indoors. This eliminates the need for separate eyeglasses and sunglasses for regular, daily use. Transitions lenses are the most well-known photochromic lenses.
  • Presbyopia: This eye condition happens as you age and results in blurred near vision. While this might sound like hyperopia (farsightedness), it occurs because the eye’s lens is less flexible and it’s age-related. Alternatively, hyperopia can affect people of any age including children.
  • Progressive Lenses: Progressive lenses are multifocal lenses that allow you to see clearly at all distances instead of just the two or three distances found in bifocals or trifocals. The transition between viewing distances is seamless.
  • Pupillary Distance (PD): This measurement is the distance between the center of one pupil to the center of the other pupil in millimeters. It’s an essential measurement to have taken when you’re buying glasses because it ensures you’ll be looking through the correct spot in your lenses.
  • RX: This is the abbreviation for prescription. 
  • Sphere: This number on your prescription indicates how much lens power in diopters you’ll need to correct your nearsightedness or farsightedness. If there is a minus sign before it, that means you’re nearsighted. If it’s preceded by a plus sign, you’re farsighted. 
  • Temple Length: Measured in millimeters, the temple length is the length of the stems or arms on either side of the frame. The measurement is taken from the hinge to the tip that sits over your ears. 
  • Transitions Lenses: These are a popular brand of photochromic lenses that transition from clear when you’re indoors to dark when you’re in sunlight. They function as both regular eyeglasses and sunglasses and protect against harmful UV rays. 
  • Trifocal: Eyeglass lenses with three regions to allow you to see clearly at far, intermediate and near distances are known as trifocals. 
  • UV Filter: This lens coating filters harmful UV radiation to protect the eyes. 

These are some of the most common vision-related terms and should give you a good base for the next time you visit an eye care professional or shop for eyeglasses or contact lenses. If you’d like more clarity on any of the subjects or have questions, feel free to stop by the Spectacle Shoppe in Kerrisdale. We’ll give you the lowdown on everything you need to know while we help you choose the perfect pair of glasses. 


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Morgan Nahanee
Morgan Nahanee


Morgan is The Spectacle Shoppe’s Lead Technician and Customer Relations Specialist as well as a Principle of Spectacle Shoppe. She is a licensed contact lens fitter and dispensing optician and has been working for The Spectacle Shoppe since 2006. She graduated from Douglas College’s two year Dispensing Optician and Contact Lens Fitting Program in 2008. From contact lens fitting to eyeglass repairs and adjustments Morgan is eager to help you with any optical needs. Connect with Morgan Nahanee on Google+