Mar
2006

Lens Choices

Glare Busters

 

In the on-going fight against glare, many eyecare practitioners and patients believe polarized lenses are the only effective solution. However, new research is deepening our understanding of glare and its causes. Along with that, advances in technology have yielded a growing array of glare-fighting lenses and lens treatments that offer comfort, improved contrast and enhanced visual acuity. Today’s glare-ware may incorporate a number of light-filtering technologies including polarization, AR coating, photochromics and mirrors, often in various combinations depending upon the visual need being addressed.

Although the presence of light is a necessity for sight, visual acuity and contrast are compromised when there is either too little or too much light available. Glare, in all its intensities, represents the latter situation—an excess of light. It creates visual interference that can range from discomfort to impairment. These problems can be controlled or eliminated with the proper lenses and lens treatments. Incorporating these features into glasses is referred to as light management and gives the patient eyewear that does more than just correct for visual acuity. Effective light management returns definition to images and is used as an amplification of visual comfort and function. It should be positioned as a feature of eyewear equal to that of a prescription.

Contrast sensitivity has been gaining recognition as a major function along with visual acuity. When a patient is in the exam chair, the prescription is determined by the size of the image that can be seen in a high-contrast situation. The real environment, though, is not necessarily high contrast. Take, for instance, newsprint. The contrast in a newspaper is far less than ideal and the lighting used when reading a newspaper can also compromise the contrast. All images are shaded in color and contrasts. The patient’s ability to distinguish that shading is their contrast sensitivity. Reduced contrast sensitivity is not limited to people with reduced visual acuity. People with 20/20 vision can still experience reduced contrast.

Perception of contrast is significantly affected by the presence of glare. Sensitivity to glare is a frequent complaint heard by eyecare practitioners. As the amount of available light increases, beyond what is optimal, the ability to determine contrast decreases.

Glare can result from either direct or reflected light. There are actually four levels of glare that can affect acuity and comfort. The light levels are measured in lumens. Ideal light situations should measure between 1,000 and 1,400 lumens. This is best represented by light in a shady area on a sunny day.


Distracting glare is reflected light. For example, it is the reflection seen on a lens surface or seen as reflections around headlights. It can occur at levels of 1,400 to 3,000 lumens. Beyond being uncomfortable, it can also lead to eye fatigue.

Discomforting glare comes from either direct or reflected light. It can occur even on a cloudy day or in any situation, of about 3,000 lumens or more, where the eye has difficulty adapting. This happens when moving from shade to sun. It causes squinting and the desire to shade the eyes.

Disabling glare is experienced when the amount of light becomes quite excessive and results in reduced vision and reduced contrast. It is sometimes referred to as veiling glare because the vision is like looking through a veil.

Blinding glare
is a result of reflected light from flat shiny surfaces, like water. It becomes polarized and increases in intensity. It is most significant because it can severely obstruct vision. Color, contrast and depth perception can be severely compromised and vision is often totally obscured.

Glare Solutions
Only polarized lenses are capable of reducing blinding glare. Polarized lenses function in two manners. First, depending on the color of the lens, the amount of brightness entering the eye is reduced. Then, the polarization of the lens absorbs and eliminates the horizontal reflected glare, while allowing the remaining light to pass through, improving acuity and contrast.

The addition of anti-reflective coating to a lens surface is another option for reducing glare, particularly distracting glare. AR coatings eliminate internal and external surface reflections and increase the amount of light reaching the eye. With conventional lens materials, the gain in transmission is about 8 percent. Higher-index materials result in less light transmission, because more light is reflected. When this is combined with the flatter curves required with the higher indices, the patient experiences discomfort. When AR coatings are applied to high-index lenses, light transmission is increased over 12 percent. This is why it is so important to include anti-reflective coatings on high index materials. The distracting reflections are greater than on the lower indices. The coatings eliminate the glare, increase the amount of light entering the eye and improve the contrast.

Ghost images are another form of distracting reflections. They are exact images created by reflections from the inside surface of the lens. They appear to the side of the object being reflected and manifest themselves most dramatically at night.

Back surface reflections cause wearers to see objects behind the lens, or the wearer, reflected into the eye. This is more pronounced with flatter inside curves and tinted lenses. Anti-reflective coatings eliminate both ghost images and back surface reflections.

It is widely accepted that anti-reflection treatments assist in night driving. By eliminating the reflections that occur at night, more light reaches the eye, aiding vision in the low light situation. Contrast is increased and the annoyances caused by glare are reduced.

Distracting and discomforting glare can also be relieved by the use of fixed tint lenses. Lenses with a transmission of 12 to 15 percent will reduce the lumens exhibited in a sunny area, to those in a shady area. With general tints, a decrease in light will result in a decrease of contrast. An additional asset to a tinted lens, though, is that by use of different colors, absorptions can be controlled to transmit the most beneficial, task specific light. In another form of light management, there is an array of light filtering technologies that can control the transmission of specific wavelengths of light. It creates customized effects and enhances contrast needs for particular activities. As an example, blue light is known to scatter in the eye. It can cause discomfort in certain circumstances. Often older people are most sensitive to blue light scatter. By attenuating blue light, the vision is more comfortable and contrast and, by extension, visual acuity are improved. Glare control in a fixed tint lens can be assisted by the use of a mirror coating. These treatments reflect light away from the lens surface. Mirrors can be controlled to reflect specific light rays, specializing them for performance.

Photochromic lenses are also useful in fighting glare. These lenses address the issue of moving from high light to low light and allow the eye to perform at its best in a variety of lighting situations without having to change lenses. Lens density changes as the eye adjusts to the change in available light. Combining photochromics with anti-reflective coatings can provide comfort in lower lumen glare situations.
In a recent study sponsored by Transitions Optical, Madeline Romeu, OD and Susan Stenson, MD measured children’s preference for Transitions photochromic lenses or clear lenses. The researchers found a reduction in the amount of squinting done by the youngsters while wearing photochromics, making these lenses the better choice for outdoor use. (Squinting, of course, is a byproduct of discomforting glare.)

Disabling and blinding glare is everywhere—on snow, water and on flat shiny surfaces such as roadways. In fact, the number-one complaint of many eyeglass wearers is the glare they encounter while driving. Unfortunately, static tint lenses, even if polarized, do not address all the lighting conditions that inhibit visual comfort while driving. Conventional photochromic lenses are also of limited use, since windshields block the UV light needed to trigger the photochromic reaction.

However, Younger Optics has just released a new lens called Drivewear solves these problems. Working together with Transitions Optical, Younger developed a polarized lens that changes color in response to both ultra-violet and visible light. This gives the lens the ability to change behind a windshield. In a vehicle on low light days, the lens will have a green/yellow color. On brighter days the lens will be copper. This is ideal for contrast and acuity while driving. Outdoors, in bright sun, the polarized lenses will change to reddish brown. Although designed primarily for improving vision while driving, the Drivewear lens can also be worn in other situations.

The range of glare-wear options is continually expanding as manufacturers introduce new lens materials and designs. As a result, there are glare-wear solutions now for nearly all patients who wear eyeglasses.

Yet contact lens wearers and plano patients can also benefit from glare-wear. They should be educated about the need to protect and optimize their visual acuity. In the case of blinding glare, it actually becomes a safety issue.

With so many lenses and treatments options now available, there’s never been a better time to recommend glare-wear to every patient. LT


Vicki B. Masliah is director of professional education for Hirsch Optical, an independent wholesale laboratory in Farmingdale, N.Y.

 

 

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