When our eyes focus on distant objects, both pupils are straight forward. As an object gets closer, the alignment of our eyes must also get closer together. This convergence for near focus is accounted for in all multifocal designs by insetting the near zone from the distance alignment. Conventional designs must provide the same near … Continued
Base curve variability is a type of dual surface design. As previously described, a lens manufactured on the optimal base curve can control the optical accuracy in a larger window of the lens and reduce aberrations. Optimizing base curves with a larger selection of smaller increments of single vision spherical curves is a huge advantage … Continued
Digital surfacing technology is always done on the back side of a lens. When a company claims dual surface design, that means the lenses are not starting with a spherical single-vision lens blank. Instead, they produce specialty molded aspheric pucks. This allows for an even more complex design and claims to have better ability to … Continued
There are many types of electronic devices to assist in frame parameters on the market today. They are all intended to give us the values of vertex, wrap, and tilt, but each has a unique set of additional features. Most devices will provide box measurements for frames as well as PD, optical center height, and … Continued
We have a variety manual devices to obtain position of wear measurements. These include various contraptions such as wrap layout charts, suction cup pantoscopic anglers, distometers, and even PD rulers. The distometer has been around much longer than digitally compensated lenses. This device measures vertex distance by resting on the closed lid and reaching an … Continued
Digital lenses are often compensated whether or not measurements are provided. An optician can pre-adjust the patient’s frame and take the actual measured values of vertex, panto, and wrap on the patient to supply in the lab order for the prescription compensation. If these custom measurements are not provided, the lens design usually uses default … Continued
There are three positions of wear that can be measured and used to calculate lens compensation: vertex distance, pantoscopic tilt, and frame wrap (also called faceform or panoramic angle). Vertex distance is measured from the back surface of a lens to the front of the eye. Vertex variations change the perceived spherical power of the … Continued
Most digital lens designs today offer a lens compensation. Compensating a prescription means the lens is intentionally fabricated with different lens powers than prescribed. Some specialty designs such as office lenses will compensate the doctor’s distance prescription to an intermediate-near format. However, most lens compensations exist to correct for common errors in the viewed prescription … Continued
The keyhole effect is the claim that processing the progressive corridor and magnification on the back side of the lens brings it closer to the patient’s eye thus producing the effect of putting your eye closer to a keyhole and broadening your view making the corridor and focal zones appear wider. Some digital lens companies … Continued
There are many optical errors that can occur with imprecise focusing of light through a lens that can reduce visual clarity, even if a lens is surfaced accurately. These aberrations are not caused by the patient’s vision, but by the lens itself. Aberrations are defined as any property of a lens that results in an … Continued
We know that the very nature of digital processing reduces many obstacles and limitations of lens curve and availability, but what else can we do with these capabilities? Optical manufactures are on an even playing field as far as surfacing equipment and ability. Every established optical lens company is now up against newer digital lens … Continued
Conventional progressive designs are created by a mold of add progression that is duplicated exactly for each patient who is fit with that lens. Conventional design can be compared to a rubber stamp that creates exact duplicates of a single design. A freeform generator has a single-point diamond cutter that can create any design imaginable … Continued
I am always careful to use the verbiage “potential for advanced design” because as digital surfacing allows for sculpting of a lens that is only limited by our imagination, I can assure you that we are still very capable of limited imaginations. In many ways freeform processing is just another way to make a lens. … Continued
The front curvature of a lens is known as the base curve. The measured dioptric power of the base curve is what the ocular back curve powers are based on to deliver the desired prescription. The sum of the dioptric power of the front and back curvatures create the total lens power. This means every … Continued
Digital lens design allows the lab to make complex curves unique per order on the back lens surface. This means the front lens surface can now be a simple spherical curve, also known as a single-vision blank. This drastically reduces required lens stock because each single-vision blank only has to have the features of base … Continued
This precision in freeform processing created by the diamond lathe leads to great benefits throughout lens surfacing. There is less degradation of the lens surface while manufacturing. These pictures compare the lens surface after conventional lap tool grinding versus the lens surface after freeform generation. The ridged opaque surface from conventional processing must be heavily … Continued
Digital surfacing has revolutionized the optical industry as an entirely new way of manufacturing prescription lenses. From blocking to generating to polishing, the freeform lens is created with specialized machinery from beginning to end. Digital surfacing is accomplished with freeform generators. Instead of a multitude of simple lap tools, freeform generation utilizes a fine point … Continued
With the lab making only simple single-vision curves, the lens pucks those curves were ground on had to be stocked in every available lens option pre-made on the front lens surface. Let’s say a lab carried ten different types of progressive designs. Now, picture each of those lens designs stocked in 11 add powers, in … Continued
Lap tools are a molded grinding instrument that is formed to the specifications of every possible sphere and cylinder power in quarter step increments and compatible with each possible base curve selection. These tools were stocked on huge rotating shelves. Approximately 4,000 tools had to be kept to accommodate surfacing and polishing of all prescription … Continued