Part 2 of our Back to Basics series on lens coatings explains the science, and benefits, behind these treatments
By: JENEAN CARLTON, ABOC, NCLC
Eyecare Business March 1, 2015
BACK TO BASICS
UNDERSTANDING ANTI-FOG AND MIRROR TREATMENTS
Part 2 of our Back to Basics series on lens coatings explains the science, and benefits, behind these treatments
BY JENEAN CARLTON, ABOC, NCLC
Have you ever stepped out of your car and had your lenses become so foggy you couldn’t see where you were walking? Perhaps you’ve entered a store and your lenses fog to the point you had to quickly wipe them off to see clearly.
Fogged lenses are more of a problem than we may realize. Most eyeglass wearers experience this nuisance and potential safety hazard in their daily lives.
Athletes and weekend sports enthusiasts are also routinely faced with the problems of fogged lenses. Can you imagine skiing down a black diamond run in Colorado and your ski goggle suddenly fogs? Or the frustration of being a basketball player and missing a shot because of poor vision caused by fogged protective lenses?
Abrupt temperature changes often result in this for patients Photo courtsey of Essilor
FOG SCENARIOS
Here are a few common scenarios that lead to fogged lenses. Riding a bicycle while wearing closely fitted sunglasses can cause lenses to fog. If the glasses fit too tightly air can’t circulate adequately behind the lenses. Another situation involves leaving eyewear in the car on a cold night then putting the glasses on in the morning for the commute to work. Even cooking can result in fogged lenses. The steam escaping from the pot or oven instantly fogs your lenses, rendering you temporarily impaired and a bit annoyed as you wait for the lenses to normalize to the room temperature and become clear.
Situations like these are no doubt irritating; however there are times when fogged lenses pose a real safety threat.
• Motorcyclists routinely face safety concerns when wearing prescription eyewear behind the face shield on their helmets. The limited airflow beneath the face shield and glasses commonly results in fogged lenses.
• Those working in industrial or construction environments are generally required to wear safety eyewear on the job. The problem with safety eyewear is these frame styles fit very closely to the wearer’s face. While the close fit protects the wearer’s eyes from the potential damage of flying debris, it can also cause a lack of airflow underneath the frames. The limited airflow allows the lenses to fog and sets up a hazardous situation for the wearer as well as coworkers.
• Patients working on projects around the home will need safety eyewear as well. The lenses on some of these frame styles are notorious for fogging, which is troublesome for the wearer. Avoiding wearing safety glasses because of fogging obviously places the wearer at risk.
WATER 101
A phase transition of water is when water changes from one state—a solid, liquid, or gas—to another state without undergoing a change in chemical composition.
• Water vapor changing to water is condensation.
• Ice changing into liquid water is melting.
• Liquid water transforming into water vapor is vaporization and evaporation.
• Water changing to ice is freezing.
• Solid water, like ice or snow, changing into water vapor without first melting into water is termed sublimation.
FOG SCIENCE
Lenses fog when exposed to quick changes in temperature. The moisture in the air and change in temperature causes condensation to form on the lens surfaces. Condensation is the change of water from its gaseous form, water vapor, into liquid water. Condensation results in tiny droplets of water, which appear as fog, to form on the lenses.
Here’s why lenses become foggy when going from the cold outdoors to the warmer indoors: upon entering the store, warm moist air comes into contact with the cold lenses. This quick change in temperature causes condensation to immediately form on the front surface of the lenses because the warmest temperature, and highest humidity level, is the air in the store.
Let’s also consider the scenario of the basketball player. In this case the condensation/fog forms on the inside of his sports goggles. Why did the fog form on the inside of the lenses this time instead of the outside? The air in a gym is likely air-conditioned. As the athlete plays the game he begins to sweat so his body can cool itself from the thermal energy created by his exertion. If his sports goggles fit tightly, and don’t allow enough airflow behind and around the lenses, this creates an air chamber behind his glasses that contains a high level of humidity and high air temperature.
Anti-fog lens treatments, coatings, and products fight fog by creating a hydrophilic lens surface. Hydrophilic treatments and coatings reduce the amount of surface tension on lenses allowing water droplets (condensation) to disperse into a thin sheet of water that is virtually invisible to eyeglass wearers.
Mirror coatings are fun, fashionable, and functional Photo courtesy of iCoat company
In this case the warmer air temperature and higher degree of humidity is behind his glasses. Because of this the fog will form on the back surface of the lenses.
Lens treatments as well as temporary sprays and wipes can keep the fog away Photo courtesy of OptiCote
QUICK FIXES
There are several products available to temporarily keep lenses from fogging. Some of these products are approved for anti-reflective lenses, and some are not. Check labels before recommending.
Some of the popular anti-fog products include: FogBuster from Hilco, available as a spray that comes with a buffing cloth or as a towelette, is good for a few hours or day, depending on application (hilco.com); Clarify Defog It cloths by Nanofilm (nanofilmusa.com); Stormin’ Norman No Fog spray (storminnormans.com); MotoSolutions FogTechDX wipes (motosolutions.com/fogtech.html); and OMS OptoChemicals ZeroFog spray (optochemicals.com).
For a more permanent solution to fogged lenses, several lens treatments have been developed. See sidebar page 92.
Mirror coatings are available in many colors, and can match or complement a frame’s color Photo courtesy of Shamir Insight
BEHIND THE MIRROR
Mirror treatments on sunwear are hugely popular right now. And for good reason. The variety and colors of today’s mirror treatments are gorgeous. Let’s look at what makes them tick.
At first glance, anti-reflective and mirror treatments seem to be different because one is nearly invisible and the other is highly visible. However, these two treatments are actually closely related.
TREATMENT CENTER
Fogged lenses are a nuisance and safety concern, but lens treatments, coatings, and solvents are available to provide long-lasting
fog-free vision. These provide a more permanent solution than the sprays and wipes mentioned in the main article.
• Crizal Optifog lenses from Essilor include a unique top layer containing fog repellent properties on both the front and back surfaces of the lens. The company reports that wiping Optifog lenses with the Optifog activator cloth activates the fog repellent layers on the lenses and provides fog-free vision. Each order comes with four Optifog Activator Cloths (a year’s supply), a polyester/polyamide knitted microfiber that contains partially fluorinated alcohol substituted glycol and phenoxyethanol. Optifog lenses are also available for prescription safety eyewear from Essilor Prescription Safety Eyewear division.
• FOG FREE from Opticote is a thermally cured treatment applied to unfinished lenses. This eliminates condensation on lens surfaces and is suitable for plastic, polycarbonate, Trivex, high-index materials, and polarized lenses. For optimal performance, Opticote recommends a periodic rejuvenation of FOG FREE coating.
• IC No-Fog from iCoat Company is an anti-fog coating that reduces the water droplets’ surface tension on fogged lenses. As a result, droplets disperse into an invisible thin sheet of water that provides fog-free vision. IC No-Fog coating application is approved for ophthalmic lenses, safety goggles, face shields, sports eyewear, and industrial applications. The treatment can be applied to any lens style including a variety of lens materials.
Anti-reflective and mirror treatments achieve different functions: AR lenses allow more light to reach the eye by eliminating reflections on the lens surface. Because of this, AR lenses increase light transmission and enhance visual acuity. Conversely, mirror treatments decrease light transmission, glare, and UV exposure.
Mirrored lenses are a fun fashion statement, provide comfort to patients with glare sensitivity, and can offer some level of privacy, depending on the type of mirror treatment used. Mirrored lenses offer privacy, as they can keep others from clearly seeing the wearer’s eyes.
However, mirror and AR treatments are made with the same equipment and processes and, for the most part, the same metal oxides. Both types of treatments are achieved with vacuum deposition methods, which was covered in Part 1 in the February issue. The difference between these two treatments is the thicknesses of the metal oxide layers deposited on the lens surface.
MIRRORED SCIENCE
With AR, the oxide layers are applied at specific thickness levels to prevent light from reflecting off of the front and back surfaces of a lens. Light transmission is increased with anti-reflective lenses because less of the light striking the lens surface is reflected. In contrast, the thicknesses of the oxide layers used with mirror treatments amplify the amount of light reflected off the surface of the lenses making the lenses appear mirrored.
Mirror treatments are available in solid, flash, and gradient options. Solid mirrors provide the maximum amount of reflectance. Flash coatings produce a more translucent effect and offer a semi-reflective finish. Gradient lenses have a mirror coating at the top of the lenses that gradually decreases in saturation to the bottom of the lenses. Double-gradient mirror treatments imply that the top and bottom of the lenses have a more concentrated mirror treatment that gradually fades to clear towards the center of the lenses.
Understanding how fog forms on lenses, and how to prevent this from occurring, assists optical professionals in discussing fog-free lens options with patients. Also, understanding the fabrication method of mirror coatings, and how eyeglass wearer’s benefit from these lenses, helps practitioners discuss these fashion-forward lenses with their patients.
Optical Coatings, Part 2
JENEAN CARLTON, ABOC, NCLC
Knowing the science behind anti-fog lens treatments and mirror coatings puts staff in a better position to talk
about these treatments with patients. Check back in the April issue of Eyecare Business for the answers.
ACROSS
(Two-word answers will have a blank box between them in the puzzle)
5. Both types of treatments are achieved with _____ _____ methods.
9. There are several products available to _____ keep lenses from fogging.
10. Mirror and anti-reflective treatments are made with the same _____ and processes.
11._____ routinely face safety concerns due to fogged lenses when wearing prescription eyewear behind their face shields.
12. Condensation results in tiny _____ of water, which appear as fog, to form on the lenses.
14. Anti-fog coatings and treatments reduce the amount of _____ _____ on fogged lenses.
17. Some anti-fog products are approved for _____ lenses and some are not.
18. Lenses may fog if _____ _____ fit too tightly.
19. Flash coatings produce a more _____ effect and offer a semi-reflective finish.
20. _____ _____, coatings, and solvents are available to give eyeglass wearers relief from fogged lenses.
22. The moisture in the air and change in temperature causes _____to form on the lens surfaces.
25. _____ _____ have a mirror coating at the top of the lenses that gradually decreases in saturation to the bottom of the lenses.
27. AR lenses _____ light transmission.
28. _____ mirror treatments provide the maximum amount of reflectance.
29. Mirror treatments _____ light transmission, glare, and UV exposure.
DOWN
1. Lenses fog when exposed to quick changes in_____.
2. Anti-reflective lenses allow more light to reach the eye by _____ _____ on the lens surface.
3. Individuals working on projects around the home also need _____ _____.
4. If glasses fit too tightly air can’t _____ behind the lenses.
6. The thicknesses of the oxide layers used with mirror treatments _____ the amount of light reflected off the surface of the lenses.
7. _____ _____ are more of a problem than we may realize.
8. The problem with safety eyewear is these frame styles fit very _____ to the wearer’s face.
13. People working in industrial and _____ environments are usually required to wear safety eyewear.
15. Condensation is the change of water from its _____ form, water vapor, into liquid water.
16. Even _____ can result in fogged lenses.
21. Light transmission is increased with anti-reflective lenses because less of the light striking the lens surface is _____.
23. Mirrored lenses offer _____ as they can keep others from clearly seeing the wearer’s eyes.
24. Anti-reflective and _____ treatments are closely related.
26. Mirror treatments are available in solid, _____ and gradient options.
![]({"src":"/media/1fqj2pnu/32015.jpg","focalPoint":null,"crops":[{"alias":"thumbnail","width":1110,"height":700,"coordinates":null}]})