Photochromic Lenses: Protecting Eye Health and Enhancing Visual Comfort

Photochromics have come a long way! Long gone are the glass photochromic lenses that we ‘put in the refrigerator’ to activate…the ones that, after time, stopped fading back to clear. You remember, our grandfathers’ photochromics!

Today, through advanced scientific advancements, we can now offer photochromic options for all needs and wants. From completely clear to dark, even cool clear lenses that change into fun-colored mirrors when exposed to UV light!

No matter the flavor, there are predictable consistencies with all photochromic lenses:

All photochromics are sensitive to temperature and light. The colder the climate, the darker the lenses will become. The warmer the climate, the less darkening effects.

The more ultraviolet light, the darker the lens, the less ultraviolet light (more infrared light), the lighter. 

This can be confusing for our patients. They would expect that the lenses would be the darkest on a hot sunny day on a beach in Florida, when in fact, they are the darkest on a cold snowy ski slope in Colorado.

In a hot sunny environment, the lens will not get as dark, but the fade back will be quicker. In a cold sunny environment, the lens will get darker, and the fade back to clear will take longer.

It is very important that we explain this to our patients to manage expectations.

When having these discussions with our patients, I am a big believer in ‘KISS’…Keep it simple, sweetheart!

The best way to discuss photochromics with our patients is to talk about eye health and comfort. 

Health: Most people know the importance of protecting our skin from the dangers of ultraviolet light. The sunscreen industry has repeatedly reminded us of this important fact. Doctors also talk about the importance of protecting our skin and promote regular check-ups with dermatologists to be safe. It is our responsibility to educate our patients about the dangers of over-exposure of UV light to the eyes. The most sensitive tissue is around the eye area, and this is where there is a high risk of non-melanoma skin cancers. Other diseases and conditions of the eyes (cataracts, age-related macula degeneration) have been linked to over-exposure to ultraviolet light.

Comfort: We understand that vision is not just about clarity, it is also about comfort. Many people have photophobia (light sensitivity) which has adverse effects on our visual comfort over time. A photochromic technology can make all the difference in this scenario. Also, as we use electronic digital devices more than ever, a photochromic technology will help reduce eyestrain, and block high energy visible (HEV) light as well. A blue-blocking technology with a yellow tint is not for everyone. While it is a great technology, many people will not be pleased with the yellow hue. A photochromic lens protects the eyes both outdoors in extreme UV and HEV environments, and indoors as well, where some HEV is emitted from the screens of our smart devices that we hold so dear.

While photochromic dyes respond the same to light and heat, they are not all the same, particularly in the quality of the dyes and the methods of manufacture. 

The various methods of manufacture are as follows:

1. In-Mass: In this method, the actual photochromic dyes are mixed in with the lens monomer so that the dyes exist evenly throughout the entire mass of the lens. Sometimes this method of manufacture can yield uneven darkness/lightness, depending on the thickness of the lens. A minus lens (particularly a high minus) may be lighter in the center and darker around the edges, and opposite for plus lenses. This method of manufacture is not as common today as it was years ago.
2. Permeation: Also known as ‘imbibing’. This is an older technique where the photochromic dyes are deposited on the surface of a clear lens blank. Then, the blank is exposed to heat to open the pores to allow the dyes to settle in. Permeation can be used on segmented bifocals (like flat-tops) and can be done on a mass scale.
3. Wafer: Most polycarbonate photochromic lenses are made this way, as poly is a thermo-plastic. Lenses manufactured this way can be very durable. In this scenario, a wafer less than 1mm thick is molded directly into the lens blank. Hard coating and other treatments can be added to the finished lens. The benefit of this method is that the dyes are shielded from the environment, remaining extremely close to the surface of the lens, yielding easy activation.
4. Spin Coating: This is a complex method of manufacture with specific conditions and unique equipment. This is one of the most common methods used today. The thin coating of photochromic dyes is applied to the top of the lens. This allows for even and controlled application of the dyes, while also keeping close to the surface, keeping the efficacy of the activation by UV light. Once this is accomplished, a hard coating is applied to protect the dyes. A great benefit of this, is that this method allows the same surface properties on a variety of substrates. In other words, it performs equally well combined with any lens material. The result is consistent, even color and density.

When asked about the most important attribute of a photochromic lens technology, most patients will state that the fade back time is the most important to them. Neochromes lenses are completely clear indoors in all materials and are color neutral in their inactivated state. It is highly recommended to add an efficient AR coating to increase light transmission to the eyes. Neochromes photochromic lenses darken in seconds (6 – 7 seconds), and fade back to clear in less than 3 minutes. Much like the natural pupil in the eye, constricting in bright sun and dilating when going indoors from the bright sun…our eyes do not do this in an instant, there is a ‘natural fade back’, if you will, without wearing eyeglasses.

The best way to dispense more photochromic lenses is to wear them! When talking about the features and benefits to the patient, nothing beats walking outside (if possible) to show them in action. All opticians, in my opinion, should be modeling eyewear with photochromics in the dispensary, even if plano…our patients will see that we believe in the technologies and walk our talk.

Everyone’s eyes will benefit!