Eyeglass Lens


Eyeglass lenses are glass or plastic optical items that fit inside eyewear frames to enhance and/or correct the wearer's vision. The magnifying glass, invented in the early 1200s, was the first optical lens used for enhancing vision. Made from a transparent quartz and beryl lens, the invention revealed the critical discovery that reflective surfaces ground to certain angles could enhance vision. Following this invention, Alessando di Spina introduced eyewear to the general populace. Due to the increasing demand for eyewear, quartz and beryl lenses were virtually replaced by glass lenses. The convex lens was the first optical lens used in glasses to aid the correction of farsightedness, but other corrective lenses followed, including the concave lens for the correction of near-sightedness, and more complex lenses for the correction of astigmatism, as well as the invention of bifocals by Benjamin Franklin in 1784.

More than 80 percent of all eyeglasses worn today have plastic lenses, but plastic lenses have not always been the lens of choice. The glass lens remained dominant until 1952, when plastic lenses were introduced. The plastic lens rapidly grew in popularity because the lens was lighter and less prone to breakage. Today, the manufacture of plastic eyeglass lenses far exceeds the manufacture of glass lenses, but the process has remained much the same for both types. Plastic as well as glass lenses are produced by successive stages of fine grinding, polishing, and shaping. While the same process is used to produce lenses for telescopes, microscopes, binoculars, cameras, and various projectors, such lenses are usually larger and thicker and require greater precision and power. This article will focus on plastic eyeglass lenses.

In the past, opticians relied on separate optical laboratories to produce eyeglass lenses. Today, there are a number of full-service optical outlets that produce lenses for customers on-site. However, optical outlets do receive lens "blanks"—plastic pieces already formed to close-to-exact size with different curves ground into the front of the lens—from optical laboratories. Blanks with different curves are used for specific optical prescriptions.

Raw Materials

The plastic blanks received from optical laboratories are round pieces of plastic such as polycarbonate approximately. 75 inch (1.9 centimeters) thick or thicker and similar in size to eyeglass frames, though slightly larger. Most finished eyeglass lenses are ground to at least. 25 inch (.63 centimeter), but this thickness may vary depending upon the particular optical prescription or "power" required. Other materials used to produce eyeglass lenses are:


Eyeglass lenses are designed in a variety of shapes to match eyeglass frames. The thickness and contour of each lens will vary

After the lens blanks are received from the factory, the optical laboratory technician selects the appropriate blanks and puts them in a lensometer. This is an instrument used to locate and mark the "optical center"—the point that should be centered over the customer's pupil—of the lens blanks.
After the lens blanks are received from the factory, the optical laboratory technician selects the appropriate blanks and puts them in a lensometer. This is an instrument used to locate and mark the "optical center"—the point that should be centered over the customer's pupil—of the lens blanks.
depending on the extent and type of correction required. In addition, the bevel surrounding the edge of the lenses will be designed to hold the lenses in the desired eyeglass frames, and some lenses, such as those for metal and rimless frames, will require more detailed edging to fit securely in the frames.

Convex and concave lenses, known as spherical lenses, require one ground curve per lens, while more curves are required to correct astigmatism. The degree and angle of the curve or curves in a lens determines its optical strength.

Various lens treatments and tints are added after the lenses are shaped but before they are inserted in frames. The coatings are added by dipping the lenses into heated metal bins filled with the treatment or tint. The treatments and tints available include various sunglass tints and colors, ultraviolet light tints, durability and impact-resistant treatments, and scratch-resistant treatments. Among the latest advances in tints is the light-sensitive tint, which combines the advantages of regular clear lenses with the protection of sunglasses. These lenses adjust to the amount of sunlight being radiated, thus providing sun protection when needed.

Various grades of plastic are used for eye wear, but the most popular is the "Feather-weight," an impact-resistant polycarbonate plastic. This type of plastic lens is more durable and 30 percent thinner and lighter than regular plastic lenses. It is also the more expensive lens. Other lens types include the standard "CR 39" trade name plastic lens—CR 39 is a monomer plastic—and the "High Index" plastic lens, which is 20 percent thinner and lighter than ordinary plastic lenses.

The Manufacturing

The following procedure assumes the plastic lenses are being made at an optical laboratory.





Byproducts or waste from the manufacturing process include plastic dust or fine shavings and a liquid polishing compound consisting of aluminum oxide, water, and polymers. The waste material is placed in metal bins for 48 hours along with sanitation compounds (vermiculite of cat litter) before disposal.

Quality Control

Plastic eyeglass lenses must meet rigid standards set by the American National Standards Institute and the Food and Drug Administration (FDA). In addition, all licensed optical laboratories belong to the National Optical Association, which requires strict adherence to prescribed guidelines regarding quality and safety.

Throughout the normal production process, plastic lenses undergo four basic inspections. Three of these inspections occur in the laboratory and the fourth occurs at the optical outlet before the eyeglasses are given to a customer. Other periodic inspections may also be advised. The four inspections involve checking the optical prescription prior to the production process and verifying the optical center placement; visually checking lenses for scratches, chips, rough edges, or other blemishes; visually checking the optical prescription before the lenses are viewed in the lensometer, and verifying optics while the lenses are in the lensometer; and measuring and verifying frame alignment with a ruler.

Where To Learn More


Impact Resistant Lenses: Questions and Answers. U.S. Department of Health and Human Services, 1987.

Periodicals and Pamphlets

"High-Speed Spindles Aid in Fabricating Plastic Eyeglass Frames with Special Finishes." Plastics Design & Processing. December 1983/January 1984, p. 21.

How Your Eyeglasses Are Made. Optical Laboratories Association.

Krasnow, Stefanie. "Athletic Specs: The Eyes Have It." Sport. August, 1987, p. 97.

More Than Meets the Eye. Optical Laboratories Association.

"Plastic Beats Acrylic for Lenses." Design News. August 18, 1986, p. 29.

Greg Ling

User Contributions:

I ve found it educative.im an optic technician.im specialised in fitting lenses in frames.would like 2 know how i can obtain Your pamphlet or books.
Can eyeglasses be made where the bificol part is clear, meaning no prescription. I keep taking my eyeglasses off to read. To avoid doing that, I wanted to know, can the bificol part have no prescription. Just plain clear glass.
thank you
Im not sure I have a good idea of exactly what your asking, but hopefully this will clear up your question. If you wear bifocal lenses currently, you shouldn't need to remove them in order to read things in you near vision. If you are wearing bifocals and your near vision is a bit fuzzy or unclear, perhaps it's time to update your prescription? If you can read a book up-close, generally about 14 - 17inches from your face, without squinting and without extending your arms in order to focus in better then you should have no need for the bifocals in the first place.

Finally, if you are not wearing bifocals and only wear glasses to correct your distance vision, and you are finding it difficult to see things clearly up-close, your Optometrist should be able to adjust you prescription, i.e. bifocals etc., and correct this issue.

To answer your question technically, it really all depends on your distance vision prescription. The lenses in your glasses have curves cut into them. Think of a perfectly round basketball. If it is perfectly round, drawing a straight line from one point to another anywhere on the ball will have the same arc, or curve measurement. If we apply this thinking to the back of the lenses in your glasses we can follow the same logic. If your prescription reads:

-2.00 -1.00 X 050
-1.00 $

then the top set of numbers is for your right eye and the bottom is for your left. The first number for the right eye (-2.00) is called the Sphere power. This number is a measurement of the arc or the curve that has been cut into every axis on the back side of your lens. This number generally is adjusted to correct the shape of your eye ball. I know that sounds a bit weird, but you can understand that when light enters the eyeball of a person who's eyeball may not be as round as it should be and instead might be bit more oblong like a football, this light hits the retina at a different angle than it should and results in unclear vision.

The second number for the right eye (-1.00) is called the cylinder power. This corrects any astigmatism you might have. Having an astigmatism just means that your cornea(the very front part of your eye) maybe isn't as round as it should be, and this is what is causing the light to fall on the retina differently than it should. This type of correction has to be more precise. This is the reason for the third number in the prescription for the right eye (050). This tells us that at every axis on the back of your right lens, a -2.00 curve has been cut. But on the 050 or 50th axis, a -1.00 curve cut into the lens. If made properly, and if you are fitted properly when you select your glasses, these two curves should cross directly over your pupil and correct your vision.

Having a bifocal with this prescription just means adding the necessary magnification to the overall prescription. Adding a +1.00 add power or bifocal to this prescription only changes the sphere power and does so algebraically. So if your right eye is -2.00 -1.00 X 050 with a bifocal add power of +1.00, then in the bifocal portion of your lens, the actual prescription would be -1.00 -1.00 X 050.

The bottom number I gave assumes no astigmatism and only gives a Sphere power. A bifocal with a +1.00 add power essentially removes the prescription from the lower portion of the left lens, removing any correction. So yes, there are ways to remove, or a better word would be balance, the prescription by using an add power that brings your lenses back to zero in the reading portion. This cannot be done with every prescription, but it will for some.

Hope I didn't confuse you. Have a good day.
I have a question regarding the lenses in my glasses which correct for nearsightedness and are also "transition" lenses. I go to a local eye doctor and her staff cuts the lenses in-house. They've already done the lenses twice for me and each time, when I take the glasses off and hold them toward a bright light, I can see very fine lines on or in the lenses, almost like someone took a comb and ran it in random patterns over the lens. The woman at the eye doc's place told me it was from the "check," a metal part of the machine that cuts the lenses. She implied that if I can't see the lines when I wear the glasses, it wasn't a big deal. I disagree as I don't see why the lines should be there in the first place. And I don't want to have a problem in the future, like after the 30 day warranty runs out. Have you ever heard of line patterns like this showing up on lenses when they've been cut properly? Thanks for any help.
is it possible to use a tinted glass with the right color spectrum instead of prescription glass lenses? I mean it wouldn't be impossible exactly you would just need the right chemical formula. My college friend and I are conducting an experiment to see if it is possible for a person to see through color tinted glass instead of a prescription. I implied that it would be possible and he said it couldn't be done.
Gordon Dunbar
I'm curious to know where the backlog of work is located in the process? Is it in the blocking or polishing or bevelling or maybe the testing or dispatch? ie. that place where there is typically the largest amount of work in process (inventory) waiting before it.
Alan Embree
Re bifocal lenses: I can see multiple irregularities in the bifocal lens portion of my glasses. I do not see the same irregularities elsewhere in the lenses. I see these curvy, irregular lines when I remove my glasses and observe them with my naked, nearsighted eye at a distance of about 12 inches. They remind me of the surface irregularities on a fresh bowl of Jello. At the optometrist office , they insist I have scratched the lenses through carelessness. After wearing glasses for about 80 years, 45 with bifocals, I think I know how to take them off and put them down without scratching them. This imperfection appears to me as though the bifocal lens were bonded to the front of the larger lens, and the bonding material had ripples in its surface before the two pieces were united, but I can't find any description of how bifocals are manufactured. Can you explain the manufacturing process or how this imperfection has occurred? And who should be responsible to fix it? Although I can read most print with these glasses when having regular check-ups I usually have to move my head slightly to look through a different part of the bifocal lens to be sure about small print. Can you tell me I'm not just crazy? I'm sure that's what my optometrist thinks.

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