|Many patients have never been offered AR lenses.|
|POINTERS ON AR BENEFITS An anti-reflective treatment can:
• Bring more light to the eye: “You will see things brighter and more clearly.”
• Reduce eyestrain when working under artificial light: “Your eyes will not be as tired at the end of the work day.”
• Offer cosmetic benefits: “Your eyes will be seen more clearly by those who look at you.”
• Cut distracting reflections from the back surface of sun lenses: “You won’t see your own eyes when wearing your sunglasses.”
• Improve night driving: “You will notice reduced halos from street lights and automobile headlights.”
|Fig. 1. Water droplet on a low surface tension lens.|
|Fig 2. Water droplet on a high surface tension lens.|
|AR LENS COSTS The average patient wears a pair of eyeglasses for 25 months. If you charge $125 for an anti-reflective (AR) treatment, this equates to about $5 per month, or $0.16 per day, for a quality AR treatment. This is a very small price to pay for improved vision, cosmetic appearance, and better night-time driving. Breaking down the cost per day will help your patients justify their purchase. Remember, a patient who has AR lenses will purchase AR in their next pair.|
Understanding the technical merits of AR treatments can help you sell them.
According to The Vision Council’s 2012 AR Lens White Paper report, while 60% of patients had a desire to purchase an anti-reflective (AR) treated lens, only 29% of them actually bought it. This indicates that many patients have never been offered AR lenses. One stumbling block for improved AR sales is that some eyecare professionals (ECPs) don’t understand the technical merits of AR treatments. It’s hard to recommend a product to a patient when you don’t fully understand it yourself. The following discussion highlights the technical points you should know about AR treatments.
Each lens material has a different index of refraction. As the index of refraction increases, the amount of reflection from each lens surface also increases. A hard resin lens reflects about 4% of the light from each surface for a total of 7.8% reflection. This means the lens is transmitting about 92%. A lens made of 1.67 index material reflects about 6% from each surface for a 12.2% total, so it transmits 87.8%. An AR treatment would bring both of these lens materials to a transmission level of nearly 100%.
The benefit of an AR treatment is increased visual acuity and contrast. This is why you should mention to patients that they will notice sharper, clearer vision through their lenses with an AR treatment compared to those lenses without it. Believe me, if you use a good quality AR treatment, they will notice!
An AR treatment is built in layers and the various layers of this “stack” have features and benefits for the wearer.
The first layer applied to an AR lens is a hardcoating that fills in the imperfections in the surfaces of the lens. This creates a smooth surface for the AR stack (layers) to be applied. It is important that the coating and the lens material are index matched. Why? When semi-finished lenses are surfaced, the lens has a manufacturer’s anti-scratch coating (hardcoating) on the front.
The surfacing lab applies its own anti-scratch formula on the backside. This is a potential problem because the AR layers added next are applied to two different anti-scratch coatings (the different front and back coatings), each with a different chemical and optical makeup and potentially a different index of refraction. This can cause issues with durability and adhesion as well as light not passing perfectly through the lens because the anti-scratch coatings have different indices of refraction. This “substrate matching” is the key to providing a superior performance. That is why many lens manufacturers recommend their own AR treatment on their lenses. For single vision lenses, hardcoating layers are added using a computer-controlled dip coating process, which ensures the identical hardcoating goes on both sides of the lens.
The AR treatment is made up of alternating layers of high refractive index and low refractive index materials. Each layer is responsible for creating the destructive interference pattern needed to knock out lens surface reflections and each layer works with different wavelengths of light in the visible spectrum. The more layers there are, the more wavelength reflections are neutralized. Higher-quality AR products have up to seven layers in their stack (on each side of the lens) with alternating layers of high- and low-index materials. Here’s an example of the first five layers of a premium AR treatment:
1st: hardcoating for adhesion, often silicon dioxide (low-index of 1.47)
2nd: metal oxide such as Zirconium Dioxide (n = 2.06) or Titanium Dioxide (n = 2.45)
To this stack, additional layers are often added such as those with oleophobic and hydrophobic properties.
Coating thicknesses are chosen to address certain wavelengths of light that make up the visible spectrum. The thickness of each layer is a quarter the wavelength of the color of light in the spectrum it is attempting to reflect. A multilayered treatment provides what is called broad spectrum anti-reflection.
OLEOPHOBIC AND HYDROPHOBIC
Premium AR treatments have an oleophobic treatment as one of the top layers. The purpose of this layer is to repel grease and oil, making the lens easier to clean. This layer is very slick, allowing a clean cloth to glide over the lens surface. The higher the quality of this layer, the less oil is deposited on the lens when it is touched.
A hydrophobic layer repels water so water droplets bead up on the lens. An untreated plastic lens has a low surface tension so a water drop spreads itself out over a wide area (See Fig. 1).
When a hydrophobic treatment is incorporated into an AR treatment, its high surface tension resists the water droplets’ attempt to flatten and forms a tight bead. Many drops will fall off the surface and the ones that remain have a hard time staying in place and are easily removed (See Fig. 2).
The hydrophobic/oleophobic treatment seals and protects the AR layers. It acts as an abrasion-resistant coating too so it protects the lenses. This outer layer does not render the lenses scratchproof, but it is very scratch-resistant.
Wiping an untreated plastic lens makes it develop a static electric surface charge that attracts dust, lint, and other debris. An anti-static property in the AR treatment allows the lenses to dissipate that charge and prevent debris from being attracted to the lenses. Without this property, lenses build debris much more quickly, requiring the user to clean the lenses more often.
An AR treatment on a lens reduces lens reflections to 1% or less. The benefits in sharpness and contrast enhancement as well as the improvement in the wearer’s quality of life are immeasurable. Understanding the technical aspects of AR treatment will help you recommend them more successfully, and that benefits everyone.
Randall L. Smith is the Opticianry Program Director at Baker College in Jackson, MI.