What is the manufacturing process for eyeglass lenses?
Optimal vision is primarily determined by the lenses in a pair of glasses. But they go on a long journey before they are incorporated into your frames. This article describes the manufacturing process for both glass and plastic lenses. What are lenses made of and how are they different from those purchased off the rack?
The production of eyeglass lenses begins with a visit to an eye care professional. After measuring your prescription, your eye care professional will create a unique vision profile for you. After selecting a suitable lens for your eyeglasses, a measurement is taken in order to determine the position of the lens inside your favorite frames. In order for the eyeglass lens manufacturer to produce an eyeglass lens specifically tailored to your needs, these data must be passed along to them so that they can produce an eyeglass lens tailored to your specific needs. But what happens next? How does vision analysis result in a modern, customized lens? First, a semi-finished lens is made. This is the point in which you have the option of choosing between plastic (also known as organic glass) or mineral glass. As a result of these two materials, eyeglass lenses are created.
Process involved in the production of lenses
It is important to note that the process of creating individualized precision lenses, such as prescription lenses, is mostly a freeform process, regardless of the manufacturer.
“Off-the-shelf” stock lenses are manufactured through a casting process, in contrast to prescription lenses. In contrast to prescription lenses, these lenses are usually chosen by the eye care professional for simple, affordable eyeglasses, i.e. reading glasses or for lenses that need to be replaced rapidly. It is important to note that these lenses are manufactured in large quantities rather than individually, unlike prescription lenses. While stock lenses are well suited to correct standard vision problems, they do not provide the same level of performance as individualized precision lenses. ECPs create detailed, comprehensive visual profiles of the wearers as the basis for manufacturing eyeglass lenses, which serve as the foundation for producing the latter.
What is the process of making stock lenses and semi-finished lenses?
In the casting process, plastic lenses are produced by combining liquid materials known as monomers with special ingredients, such as UV absorption, to create semi-finished lenses or stock lenses. As soon as the mixture has been poured into molds, it is hardened and processed to reduce residual stress. Once the semi-finished lens has been processed, it is ready for use. For stock lenses, the lens is coated hard and additional coatings can be applied as requested.
Glass lenses are produced in a slightly different manner. As a first step, quartz, potassium carbonate, soda, and oxide are melted at 1400° to 1500° C to form a glass mixture. In the next step, the front surface of the glass block is processed. A diamond grinding tool is used to give it its exact shape, while polishing gives it the necessary transparency. After this, it is pressed to form a round glass block that is approximately one to three centimeters thick. Having already ground one side of the semi-finished lens, we have a transparent semi-finished lens.
Manufacturing bifocal lenses in plastic and glass
An eyeglass lens with a bifocal field of vision allows one to see up close objects and the other to see away. There is a wide range of materials available to make bifocal lenses, but the production processes vary enormously depending on the material. In glass bifocal lenses, an additional lens is integrated into the semi-finished lens, which is of equal power to the main lens on the upper half while the near-vision area is of greater power on the lower half. Initially, the additional lens is ground and polished on its back surface. The curved side of the additional lens is then inserted into the existing indentation of the main lens. As a result, the additional lens is melted and ground together with the main lens until only one lens appears. After this, the front and back surfaces of the semi-finished bifocal lens are ground and polished to a desired level.
A plastic bifocal lens is significantly easier to manufacture than a glass bifocal lens. Due to the strong curvature of the relevant area, a second lens is not necessary to achieve the near vision power as with glass bifocal lenses. This curvature is achieved by placing the semi-finished lens into a suitable mold, which is then cooled.
The production of varifocal lenses
If we are to develop varifocal lenses (also known as progressive lenses), we must determine how the lenses will be used: Will the wearer place special demands on them, such as working in front of a computer screen? When calculating a lens design, a large number of factors must be considered, much as when solving a math equation with hundreds of unknown variables, to determine if the lenses will be worn during everyday activities. The production of the lens is therefore a complex process. In order to provide the semi-finished eyeglass lens with its calculated design, a special grinding machine is used. Varifocal lenses are optimized through a number of test phases before batch production begins. Varifocal lens designs are repeatedly adjusted until the first prototypes are available for testing. Test wearers are asked to put these lenses through their paces in order to ensure wearer tolerability. It is only after the test wearers have been satisfied with the particular lens design that batch production and marketing can begin.
Personalized lenses that fit your specific needs
Healthy eyes require approximately 25 minutes to adjust to the dark after switching from daytime vision (photopic vision) to nighttime vision (scotopic vision). Light-to-dark vision is accomplished by our rods, the eye’s sensory cells; the eye’s rods are responsible for the light-to-dark vision we see. As a result, the pupils increase in size so that as much light as possible can enter. Healthy eyes are able to adjust easily to changing light conditions at any time. In addition to hereditary diseases, certain medications, injuries, and vitamin A deficiencies, limited vision may also be a result of a vitamin A deficiency. In reduced lighting conditions, pupils need to dilate more, resulting in loss of depth of field and limited spatial vision, as well as exhaustion from reflections and poor contrast. This is a problem that affects a considerable number of people who wear glasses.
It is also important to note that our light-and-dark vision plays an integral role in ensuring our safety on a plane. The cabin lights are dimmed during takeoff and landing in order to enable passengers’ and crew members’ eyes to adjust immediately to the changed light conditions in case of a crash, saving precious seconds if a crash occurs.
What to do if your vision is restricted due to vision problems or eye diseases
While “off the shelf” lenses are suitable for a wide variety of activities and visual defects, a perfectly customised pair of glasses can offer even greater benefits. In contrast to stock lenses, which accommodate the visual point of each eye, the actual fitting of spectacle lenses in front of the eye is not taken into account at the time of fitting, regardless of the frame. In order to ensure that the wearer enjoys optimum, natural vision, lens production must incorporate how the spectacle wearer appears through their frames. The optician will need to identify many other important facial parameters in addition to the visual point in order to accomplish this task – all with an accuracy as small as ten millimeters. With more information about the wearer, it is possible to optimize the lens design more precisely. A measuring device is also beneficial, as it prevents “data transfer errors” from occurring.
In order to obtain relaxed and natural vision, it is crucial to attain the perfect harmony between frames, lenses, an individual’s visual needs and the shape of the wearer’s face. This is especially true for individuals who have older eyes or less common defects of vision. By using freeform technology, the spectacle lens wearer has access to a significant amount of personal data and, using complex mathematical calculations, is able to create lenses that are manufactured and fitted precisely enough to ensure that their chosen frames offer optimum vision. As a result, you are able to achieve clear vision across a large visual field with a wide range of distances while maintaining outstanding wearer tolerance. Individualized lenses differ more significantly from stock lenses the more complex and unique the situation is.
