In the next few months, opticians will focus on different aspects of lens manufacturing and surface treatment to gain an in-depth understanding of some of the latest technologies and equipment involved.
Lens manufacturing is essentially a process of shaping, polishing and coating transparent media to bend light and change its focal length. The degree to which the light needs to be bent is determined by the actual measured prescription, and the laboratory uses the details contained in the prescription to manufacture the lens.
All lenses are made from a piece of round material, called a semi-finished blank. These are made in batches of lens casters, probably mainly made of finished front lenses, and a few are made of unfinished materials.
For simple, low-value work, semi-finished lenses may be cut and edged in practice [shape fits the frame], but most practices will use prescription laboratories for surface treatment and more complex high-value work. Few opticians can perform surface treatment on semi-finished lenses, but in practice, finished single vision lenses can be cut into shapes.
Technology has changed every aspect of the lens and its manufacturing. The base material of the lens becomes lighter, thinner and stronger, and the lens can be colored, coated and polarized to provide a series of properties for the finished product.
Most importantly, computer technology enables the manufacture of lens blanks to a precise level, thereby creating precise prescriptions required by patients and correcting higher-order aberrations.
Regardless of their characteristics, most lenses start with discs made of transparent materials, usually 60, 70, or 80 mm in diameter and about 1 cm in thickness. The blank at the beginning of the prescription laboratory is determined by the prescription to be processed and the frame of the lens to be installed. Low-value single vision prescription glasses may only require a finished lens selected from the inventory and cut into the shape of the frame, although even in this category, 30% of the lenses require a customized surface.
More complicated tasks are best done by skilled opticians and laboratory technicians in close cooperation to select the best products for patients, prescriptions and frames.
Most practitioners know how technology has changed the consulting room, but technology has also changed the way prescriptions reach manufacturing. Modern systems use electronic data interchange (EDI) systems to send the patient’s prescription, lens selection, and frame shape to the laboratory.
Most EDI systems test the lens selection and possible appearance effects even before the work arrives in the laboratory. The shape of the frame is tracked and transmitted to the prescription room, so the lens fits perfectly. This will produce more accurate results than any preload mode that relies on frames that the lab may hold.
After entering the laboratory, the glasses work will usually be marked with a bar code, placed in a tray and prioritized. They will be placed in pallets of different colors and transported on carts or more conveyor systems. And emergency work can be classified according to the amount of work to be done.
The work may be complete spectacles, where the lenses are manufactured, cut into the shape of the frame and installed in the frame. Part of the process includes surface treatment of the blank, leaving the blank round so that it can be trimmed into a frame shape in other places. Where the frame is fixed during the exercise, the blank will be surface treated and the edges processed into the correct shape in the practice laboratory for installation in the frame.
Once the blank is selected and the job is barcoded and palletized, the lens will be manually or automatically placed in the lens marker, where the desired optical center position is marked. Then cover the lens with plastic film or tape to protect the front surface. The lens is then blocked by an alloy lug, which is connected to the front of the lens to hold it in place when the back of the lens is manufactured.
The lens is then placed in a molding machine, which shapes the back of the lens according to the necessary prescription. The latest development includes a barrier system that glues the plastic block holder to the taped lens surface, avoiding the use of low-melting alloy materials.
In recent years, the shaping or generation of lens shapes has undergone tremendous changes. Computer numerical control (CNC) technology has shifted the manufacturing of lenses from an analog system (using linear shapes to create the required curve) to a digital system that draws tens of thousands of independent points on the surface of the lens and produces the precise shape required. This digital manufacturing is called free-form generation.
Once the desired shape is reached, the lens must be polished. This used to be a chaotic, labor-intensive process. Mechanical smoothing and polishing are performed with a metal forming machine or grinding disc, and different grades of grinding pads are glued to the metal forming machine or grinding disc. The lens will be fixed, and the grinding ring will rub on its surface to polish it to the optical surface.
When pouring water and alumina solution onto the lens, replace the pads and rings manually. Modern machines create the surface shape of the lens with high precision, and many machines use additional tool heads to smooth the surface to achieve a smooth finish.
Then the generated curve will be checked and measured, and the lens will be marked. Older systems simply mark the lens, but modern systems usually use laser etching to mark and other information on the surface of the lens. If the lens is to be coated, it is ultrasonically cleaned. If it is ready to be cut into the shape of a frame, it has a fixed button on the back to enter the edging process.
At this stage, the lens may undergo a series of processes, including tinting or other types of coatings. Coloring and hard coating are usually applied using a dipping process. The lens will be thoroughly cleaned, and the color or coating index will match the lens and material.
Anti-reflective coatings, hydrophobic coatings, hydrophilic coatings and antistatic coatings are applied in a high vacuum chamber through a deposition process. The lens is loaded on a carrier called a dome and then placed in a high vacuum chamber. The material in powder form is placed at the bottom of the chamber, absorbed into the atmosphere of the chamber under heating and high vacuum, and deposited on the lens surface in multiple layers of only nanometer thickness.
After the lenses have completed all the processing, they will attach plastic buttons and enter the edging process. For simple full-frame frames, the edging process will cut the contour shape of the lens and any edge contours to make it fit the frame. Edge treatments can be simple bevels, grooves for super-assembly or more complicated grooves for in-line frames.
Modern edge grinding machines have been developed to include most frame modes and include frameless drilling, slotting and reaming in their functions. Some of the most modern systems also no longer require blocks, but instead use vacuum to hold the lens in place. The edging process also increasingly includes laser etching and printing.
Once the lens is finalized, it can be placed in an envelope with detailed information and sent. If the work is installed in the prescription room, the lens will continue to pass through the glass area. Although most practices can be used to glaze frames, off-site glazing services are increasingly being used by practices for high-value lenses, in-line, ultra and frameless work. Indoor glass can also be provided as part of a glass packaging transaction.
The prescription room has experienced glass technicians who can use all the necessary tools and patterns, such as Trivex, polycarbonate or higher index materials. They also handle a lot of work, so they are good at creating perfect jobs day in and day out.
In the next few months, Optician will study each of the above operations in more detail, as well as some of the available services and equipment.
Thank you for visiting the optician. To read more of our content, including the latest news, analysis and interactive CET modules, start your subscription for just £59.
With all the drama of the pandemic still being played out, it is not surprising that there are some interesting trends in eyewear design and retail in 2021…
Post time: Aug-27-2021