Bright Ideas for Avoiding Consumable Mistakes

By Julie Bos
Creating a lens that meets specific prescription requirements can be a complex undertaking. There are multiple steps in the process and that can mean numerous areas for mistakes—especially in the area of consumables.

Some of these mistakes are caused by simple human error. Others are caused by labs’ effort to make up some time; and a few are the result of trying to save money or stretch products beyond their useful life.

In our search to understand the most common mistakes labs make, we sought the advice of three industry experts: Al Bednar, director of sales and technical services at Practical Systems, Inc. (PSI); Steven Schneider, sales manager of ophthalmic consumables at SatisLoh; and Tim Spangler, vice president of operations and international sales at DAC Vision. Consider their advice for how to clean up your consumables process while increasing your lab quality.


Common Mistake: Contaminating the lens when applying surface-saver tape. The most common mistake labs make when applying tape is touching the adhesive side of the tape with their bare hands. When the oil from the skin gets on the tape surface, it can contaminate the surface and create a barrier that may prevent proper blocking adhesion.

Recommendations: Encourage the use of cotton gloves. This not only prevents oils from depositing on the lens, it offers a clean, oil-free barrier between an operator’s hands and the lens when rubbing out tiny air bubbles and wrinkles. Remind operators to be diligent about keeping their hands clean, dry and free of possible contaminants. The most common culprits are hand lotions and other products that can transfer to the lens surface or tape during handling. Consider using an in-line air blower and filtered, compressed air to gently remove dirt or debris from the lens before applying the tape.

Common Mishap: Getting too many wrinkles from surface-saver tape.

Recommendation: Consider switching tape products.

If your tape is wreaking havoc with wrinkles, it may be too thick for your lenses. Ask your supplier to suggest a different variety that still meets your budget and quality requirements preferably a tape that is more pliable, elastic and better able to form to your type of lenses.

Lens Blocking

Common Mistake: Overusing dirty alloy.

Alloy that is full of dirt and debris won’t solidify as it should a problem that causes instability and inconsistency when stabilizing the lens. This often occurs when labs don’t replace their reclaimed alloy often enough, since the more the alloy is used, reclaimed and reused, the more dirt and debris is added to the mixture. What’s more, simply adding new alloy to an already dirty mix doesn’t necessarily solve the problem.

Recommendations: Recycle your blocking alloy at least every six to 12 months (depending on your individual production levels).

Skim off the accumulated dross slag from the top surface of the alloy reservoir every day. Dross slag can cause lenses to be exposed to higher temperatures, which can cause heat-related issues or damage to the lens. It can also wreak more havoc by getting into the lines of the blocker, which can damage the blocker itself.

Common Mistake: Making the metal alloy too hot.

In order to achieve proper melting, many labs make their metal alloy too hot. Recommendation: Keep your alloy temperature between 120-125° F. If this temperature doesn’t properly melt your alloy—and you’re tempted to turn up the heat—think twice. Doing so may help compensate for a dirty mixture but may run the risk of damaging the lens.

Common Mishap: Waxy residue on lenses.

When wax residue remains on the lens surface, your lab may have trouble effectively applying a back-side or anti-reflective coating. Recommendation: Use surface-saver tape and rinse the lens multiple times. Always use a quality surface-saver tape in conjunction with a lens-compatible cleaner that removes oil-based contaminants. In addition, make a point to clean the lens in multiple baths of warm water to melt off any remaining wax residue.

Generating the Lens

Common Mistake: Not giving the blocking mechanism enough time to harden.

This shortcut can cause lens instability, which can lead to incorrect curvature, incorrect power or a deflection. Recommendation: Don’t shortcut your process.

You’d never remove a cake from the oven before it was done, and the same is true for curing blocking mediums. Always make sure you wait at least 30 minutes for the blocking medium to fully harden.


Common Mistake: Shortchanging the fining time.

Because fining pads are designed to wear down over time—with aggressive removal at first and smooth finishing toward the end—every second counts. Therefore, shortchanging the time may not leave the lens as smooth as it could be—or worse, leave you with deep scratches that won’t come out during polishing.

Recommendations: Select the correct finishing pad, identify the proper fining time needed and stick to it. Talk to your pad supplier to get their recommendations for time, speed and pressure, depending on the specific pads you’re using. Then, make sure there’s no deviation. By seeking out shortcuts, you may actually break or damage the lens—and end up creating more work for yourself in the long run.

Monitor your water temperature and quality. Properly maintained machines with a regular flow of chilled water (55-65 degrees Fahrenheit) onto the pad surface is also vital. Tap water temperatures, especially in the south, can rise to as much as 90-95 degrees in the summer, which is considered too high for good fining performance. You should also consider a lens fining additive for your water.


Common Mistake: Overusing polish.

Labs often try to run the polish for longer than it’s intended—often trying to run the same material for three to four weeks. Unfortunately, this overused polish will break down and lose its effectiveness.

Recommendations: Choose your polish carefully, based on your most frequently used lens material.

If your lab processes 80 percent polycarbonate, choose a polish that has a chemistry background for polycarbonate, and remember to replace your polish after every 300-400 lenses. Develop a consistent schedule for changing the polish, as well as the filters. It’s also important to maintain proper Baumé and temperature (ideally 55-65 degrees Fahrenheit); both should be checked throughout the day by using a Baumé gauge and thermometer.

Maintain your polish carefully. Monitor your polish temperature (which should be between 55 and 65 degrees Fahrenheit) and make sure the temperature is within five degrees of your fining water, so you don’t cause thermal shock and cause damage to the lens. You may also want to consider investing in a central slurry system to manage multiple polishing machines—an effort that helps you maintain consistent temperatures while adding filtering capability.


Common Mistake: Washing with dirty water.

If you manually wash your lenses and don’t change your soapy water or sponge often enough, you’ll likely be putting more dirt back on the lens instead of removing it. Recommendation: Replace your wash water and sponge frequently.

Make sure your water is warm and soapy, and change it and your sponge every hour. If your wash area is staffed by inexperienced personnel, educate them on proper wash techniques and the value of quality processes.


Common Mistake: Finishing pads that don’t stay in place.

When a finishing pad doesn’t adhere properly (e.g., on super hydrophobic lenses), it can cause the lens to be edged off-axis.

Recommendation: Identify the best finishing pads for your lab.

When it comes to finishing pads, one size does not fit all. Ask your suppliers for recommendations about the best ones for your lab, based on your specific volume of lens types and edging equipment.

Common Mistake: Poorly maintained cutting mechanism.

Many times, labs try to get more life from their diamond cutter than it can offer. This dull edge no longer delivers clean edges, and outputs lenses with jagged edges—or worse, creates lenses that break. Recommendation: Don’t try to extend the life of the mechanism to save money. Develop and adhere to a good maintenance schedule for changing diamond wheels or blades. For wet-cut edgers, it’s also important to maintain proper coolant flow.

Back-Side Coating

Common Mistake: Dirty back-side coating.

If you’re seeing poorly coated lenses with small dust particles, specks, air bubbles and imperfections on the lens surface, a dirty machine or dusty atmosphere may be to blame. Recommendation: Be smart about the location and care of your back-coating machine.

Whenever possible, isolate the machine to an area in the lab you can keep clean. Consider adding an air-filtering machine to further remove dust and debris in the air.

In addition to choosing an environmentally appropriate location for your equipment, make a point to regularly maintain the machine to assure maximum pressure and light exposures. In addition, always maintain the chemicals at the recommended levels, and use a quality supply of alcohol and de-ionized water.

“The main thing is focusing on being more proactive in what you’re doing with your consumables processes—instead of waiting until you’re making bad lenses to figure out what is going wrong,” said Bednar. “Routine maintenance, cleanliness and careful review of each step in the process will go a long way to ensuring high quality lenses for years to come.”


Labtalk June 2020