Welcome to our continuing series of Credit Educations Courses for Opticians.

This course has been approved for one hour of credit by the American Board of Opticianry. No fee is required for ABO credit.

Learning Outcomes:This course is presented at a beginner level for dispensers involved in working with frames and lenses. It can also be used as the basis for a staff training session on working with three-piece mounts.

At the conclusion of the article, the participant should be able to:

1. Explain to customers the history of three-piece/rimless eyewear.

2.Understand what drilling equipment and dispensing tools are needed to work with rimless in house.

3. Work with the drilling equipment and tools to minimize re-dos and produce patient-pleasing results.

4. Understand special challenges and opportunities associated with using a variety of lens materials in three-piece mounts.

5. Train staff so they can be more competent and confident in working with rimless eyewear.

Test procedures: Read the article and then click on the "Take The Test" button at the bottom of the page. This will open a new window with a test consisting of 15 questions. To receive ABO continuing education credit, respondents must correctly answer 12 of 15 test questions. Simply click on the best answer for each question and click the submit button at the end of the test. Your test answers will be automatically sent to Seiko Optical and we will send your CEC or notify you of test failure within 7 to 10 business days.

Note: Some states do not accept home study courses for continuing education credit. Check with the licensing board in your state to see if this course qualifies.

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Understanding Three-Piece Mountings

Introduction

Rimless mountings are one of the fastest growing eyewear styles in the marketplace. Manufacturers are continually introducing new styles and materials, and patients like the appearance and lighter weight that rimless mountings provide.

This Continuing Education course explores the history of rimless mountings, showing that "everything old is new again."

The course also addresses how different materials perform when placed in rimless mountings. This is important to the patient, who may think a rimless mounting will be as durable as a fully rimmed frame. The patient may also not be aware of issues such as lens thickness (based on their Rx). Some additional lifestyle questions and explanations may be necessary to ensure that the patient has realistic expectations.

In addition, the course covers finishing of rimless mounting jobs, and provides information on tools available not only to fabricate the job, but also to adjust the mounting while dispensing.

We hope this course helps you provide your patients with the highest quality rimless mountings, and allows you to profitably grow this facet of your business.

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The first eyewear frames were made out of whatever material was easiest to shape into form. The British Museum has numerous examples of eyeglass frames made of wood, slotted so lenses could be inserted. With the lens in place, the slot was tied with common twine to hold the lens in place. As artisans became more skilled, metal frames became popular, using metals that were easy to shape or inexpensive. In 1867, a U.S. frame maker named John Jacob Bausch stumbled across a piece of rubber in the road on his way home for lunch. Noting how durable and tough the material was, he began making frames out of rubber. His rubber frames became the foundation of what would become Bausch & Lomb, one of the world's largest optical manufacturers.

For centuries, the only people wearing eyeglasses were clergy, simply because only priests could read (most lenses were plus powers to correct presbyopia). When Guttenberg invented the printing press, the need for reading glasses spread beyond the clergy. Eyeglasses were expensive and limited to the wealthy.

Eventually, they dropped in price and their use spread to the general population. Here, once again, class distinctions came into play. Wealthy persons wanted eyeglasses that set them apart from common folks. This led to frames made of gold or silver. In a rudimentary way, this represented the first stirrings of a relationship between eyeglasses and fashion.

Frames vs. Mountings

The first attempts to create lightweight, inconspicuous rimless eyewear came about in the late 1800s, and a new term was needed for this different way of holding lenses in front of the eyes. The name "frame" had been coined because it defined what eyeglass frames did. They framed lenses, much like a frame around a painting or photograph.

With rimless, the apparatus holding lenses needed a different term. "Mountings" became the most used term and the practice continues to this day. When referring to the hardware for rimless eyewear, the term is mounting, not frame.

Popularity of rimless Rimless became popular in the years prior to World War I with the advent of rimless pince-nez mountings (Fig. 5, p. 5). These were rimless lenses held in place with a simple pincher-like fastener that gripped the nose, eliminating any need for temples (some pince-nez had a frame around the lens). President Franklin Roosevelt, following a fashion set by his cousin President Teddy Roosevelt, was one of the last modern personages to favor this style of eyewear.

Following the pince-nez craze in the period from 1920 to 1950, rimless mountings in a more conventional design became the most popular eyewear.

Pince-nez mountings were difficult to keep in place. One manufacturer boasted its pince-nez mounting was superior because glasses remained firmly on the nose when the wearer sneezed. As refractionists began dispensing cylinder lenses to correct astigmatism, the precarious teetering perch of pince-nez eyewear was inadequate to properly align cylinder lenses. This led to development of the first three-piece rimless mountings. This style was followed by two other significant evolutions in rimless eyewear.

The first was development of the Shurset mounting (see below). This rimless design greatly increased the stability of rimless eyewear by connecting the bridge and temple components, adding structural integrity to the eyewear. The next development in rimless was the Numont, a further refinement of the Shurset that eliminated a temporal screw. This was primarily a cosmetic improvement.

The popularity of rimless eyewear during the first half of the 20th century came about for two reasons. All lenses were glass and glass lenses were heavy. The lighter comfort provided by rimless eyewear became the preferred choice.

The second reason involved fashion. In those days, eyeglasses were not considered to be a fashion item. The primary concern was to have the most inconspicuous eyewear possible. Rimless proved an ideal way to answer that need. For the past 20 years, the most used form of rimless has been mountings that hold the lenses in suspension with a stretched nylon cord fitting in a shallow groove around the lens. The term for these mountings is semi-rimless.

The current fashion trend of three-piece mountings is a throwback to the roots of rimless eyewear, revealing that, in fashion, the past is often prologue to the future.

Processing Challenges

For obvious reasons, rimless eyewear requires greater structural integrity from lenses since the lenses must hold the completed eyewear together. The current wide range of plastic lens materials, with each material having varying physical properties, makes the choice of lens material for rimless eyewear a most important consideration.

Performance of rimless eyewear under normal wearing conditions can vary greatly. The two primary factors are:

1) the design and construction of the mounting hardware and

2) the strength and integrity of the lens, primarily determined by physical properties of the lens substrate.

Rimless three-piece mountings have become the most labor-intensive finishing operation in a laboratory. Even with the newest sophisticated computer-controlled drilling devices, mounting lenses in rimless can consume two to 10 times more operator time and produce considerably greater spoilage than inserting lenses in metal or zyl frames. Another major concern for labs has been the increased number of customer re-do orders because of cracked lenses in three-piece mountings. As a result, labs have developed strong preferences regarding which lens materials they prefer to process for three-piece mountings.

Selecting Materials

The structural stresses exerted on lenses mounted in three-piece mountings can exceed the lens' ability to resist cracking or breaking. Labs report the number of re-do orders for replacing broken or cracked lenses in three-piece mountings is two to 10 times more than for any other reason. That is one reason many labs now stress the importance of using specific lens materials for three-piece mountings.

CR-39. This was initially viewed as an ideal material for rimless. Most rimless in the years following World War II were either Shurset or Numont mountings. These designs were relatively stable because stress from the temples was supported by structurally strong arms connecting the temple hinge and the bridge. The recent fashion trend to three-piece mountings relies totally on the structure of the lens to absorb stress and strain. Conventional plastic lenses are proving not to be up to the task.

Polycarbonate. The superior strength of polycarbonate made it a first choice for lenses to be used for three-piece mountings. British labs actually have adopted a policy of only processing polycarbonate for three-piece mountings. Polycarbonate, as might be expected, has the strength and integrity to withstand the stresses common to three-piece mountings far better than CR-39 and has a higher index (1.59).

Trivex. A new material called Trivex with an index of 1.53 was developed by PPG and is currently being produced by three lens manufacturers: Younger Optics, Hoya Lens, and Thai Polymer (not yet available in the U.S.). Trivex lenses are comparable in strength to polycarbonate. Both Younger and Hoya have conducted considerable research on the suitability of Trivex lenses for rimless, which is proving to be a primary use for these new lenses.

MR-10 resin (1.67 index). This is an improved plastic lens material developed specifically for use with three-piece mountings or in any situation where super-tough lenses are desired. Documented tests indicate the tensile strength (determined by pulling the mounting away from the lens) of MR-10 is 50 percent stronger than polycarbonate and three times stronger than conventional plastic.

The material has greater flexural strength, which means the lenses are more resistant to breaking when bent. The higher index favors stronger minus corrections since the lenses will also be roughly 20 percent thinner than polycarbonate. The material takes a high edge polish, always a desirable cosmetic addition for rimless. Thinner edges resulting from the higher index make it possible to mount stronger corrections in mountings with a fixed pin length. These can be a problem with lower index materials like poly or Trivex. At this time, Seiko is the only manufacturer using MR-10 resin for its lenses.

Drilling Equipment

When CR-39 lenses came into favor, labs found them easier than glass to mount in rimless mountings. All it took was a small hand-held drill to assemble the occasional rimless mounting going through a lab. The recent popularity of three-piece mountings, combined with the wide range of lens fastening devices, has complicated the job of drilling holes far beyond the simple ability to drill a few holes.

Modern rimless mountings require precise locating of each hole, exacting control of the diameter of the hole and accurate angling of the hole itself, relative to the lens surface. Unless each of these parameters precisely follows the frame manufacturer's specifications, positioning of the finished eyewear on the face will not be what the dispenser requires. Equally important, wearing performance of the eyewear can be compromised. There's nothing as annoying as a three-piece mounting with loose screws or fastenings. The inevitable result is a visit back to the doctor or optician, a major annoyance to both patient and dispenser.

A variety of drilling units is now available, ranging from simple hand-held units that rely completely on the skill and delicate touch of the operator to sophisticated, computer-controlled units costing thousands of dollars. Most three-piece mountings require anywhere from four to eight holes, and the slightest misalignment of one hole can easily ruin a $50 lens. As a result, dispensers face two choices--invest in the proper equipment and develop the skill to operate it or leave it to the lab to mount rimless lenses.

One clever system for drilling and notching rimless lenses involves working the lens with the edging block still attached to the lens. This permits precise centering and control of the lens during the edging or notching operation. This system provides special jigs to hold edging blocks used with most edgers.

Care and caution does not stop with drilling the holes. It's important that the edges around the hole on both sides have no rough edges. This requires smoothing or chamfering the hole's edges with a round diamond burr or a diamond rat-tail file. The best mountings use a screw assembly that has a "top hat" plastic bushing that rests partly in the hole and partly against the lens surface. These keep any metal part from actual contact with the lens itself.

Dispensing Tools

Even wise dispensers who leave the risks of mounting lenses in three-piece mountings to the laboratory still face problems when dispensing these relatively fragile eyeglasses. The challenge of adjusting rimless and three-piece mountings requires having the proper tools that enable dispensers to make adjustments to the hardware without putting undue stress on the holes or the lens itself. Adding to the complications is the fact that many three-piece mountings are made of titanium or other super-strong metals that are difficult to bend or reshape. Having the right tools is essential, and tool manufacturers have risen to the challenge.

Tool suppliers have developed specialized pliers for adjusting rimless mountings. One company produces a frame adjusting plier that comes with three sets of nylon replacement pads, each with a differing profile to fit virtually all three-piece designs. Using the proper nylon pad for the mounting, the pad fits over the drill mount hardware on the temple. The plier is squeezed so the lens and hardware are gripped securely. Using the dispenser's hands or another nylon jaw plier, temples can be adjusted or pantoscopic angle can be altered. When adjusting the position of nose pads, the plier is used to grip the bridge so the pads can be adjusted by hand or with another plier.

Maintaining proper axis with cylinder lenses is another important consideration. If the holes are not correctly positioned, the axis will be incorrect, and no axis aligning plier can correct it.

Special Shapes

Three-piece mountings and other rimless mountings offer dispensers another useful advantage. Rimless mountings make it possible to change the shape of the lens to accommodate special needs. One example is replacing a vertically shallow shape with a deeper shape more suitable for progressive lenses. Altering lens shapes in rimless eyewear also makes it possible to custom-design special lens shapes for fashion reasons.

Rimless eyewear and three-piece mountings in particular have become a preferred choice for many eyewear consumers. These fashionable yet fragile eyeglasses are providing dispensers with opportunities to design and dispense the lightest eyewear possible.

Mounting lenses in rimless hardware without the stability of a frame around the lenses requires increased support from the lenses themselves, and this requires using the strongest lens materials possible.

The delicate construction of three-piece mountings imposes a need for special skills in dispensing these highly popular mountings. Retail offices with edging labs are advised to consider adding dedicated drilling equipment for processing three-piece mountings or to let their wholesale lab assume the risk of assembling them.

This concludes the article. Click the button below to take the test.