Optical filters allow only certain parts of light to pass through which can be a very effective tool for a variety of optical uses, including vision therapy and for our main focus, low vision. There are colorful filters and polarized filters, each serving their own purpose and these features can be combined to make colorful polarized filters. The type of filter that the eye doctor recommends depends on a variety of factors, including the patients’ needs or whether it’s for outdoor or indoor use. By adding this tint to your low vision care, it can enable you to read more clearly, identify people’s faces, avoid falling and other accidents, and overall enhance your lifestyle.
Filters are available in different colors and are used in different ways, depending on the patient and the light conditions. The color of the filter is used as a selection system, allowing certain colors to pass through while preventing other colors from doing so. In order to understand filters, it is important to note that there is scientific research behind colors and the way we perceive them. The rainbow as we know it has different colors due to different wavelengths of light (measured in nanometers, as seen below) that is visible to the human eye. Beyond the rainbow there are other wavelengths such as infrared on one end of the spectrum and ultraviolet on the other. You may have heard of filters available in glasses to filter out ultraviolet rays, and this is in order to protect our eyes from harmful wavelengths that are beyond the visible light spectrum.
The visible light spectrum can be seen as follows:
Yellow filters are instrumental in increasing contrast between the text or object that you’re looking at and its background. In addition to yellow, orange, amber and other short wavelength colors are used. Due to the fact that yellow is in the middle of the spectrum of visible light, the yellow filter separates between short wavelengths and long wavelengths, thereby increasing the contrast. Yellow tint is also used in Escoop glasses, recommended for people with early stages of age related macular degeneration. To learn more about this visual aid, please click here.
There are a variety of conditions that can affect contrast sensitivity. The traditional eye chart has good contrast with black letters on a white background, but not everything that we view in day to day life has a stark contrast between the target object or the text we’re reading, and the background around it. Some people have low contrast sensitivity, making it hard to distinguish between what they are reading and what is around it, especially if what they are viewing does not have good contrast to begin with. There are ways that eye doctors test a patient’s contrast sensitivity. One way is giving the patient an eye chart to read off of, which has low contrast between the letters and the background, as seen below:
There are certain conditions that reduce contrast sensitivity, these include, but are not limited to:
Each condition will have a different effect on contrast sensitivity and each person will experience that in their own way, however there are certain filters that are good for certain conditions. For example, people with retinitis pigmentosa tend to struggle greatly with contrast sensitivity issues and studies have shown that yellow filters are very helpful for improving their visual abilities, especially in low illumination conditions.
Polarizing filters are a special type of filter that help reduce glare in patients, preventing discomfort from the effects of glare. Many people complain of glare affecting their daily visual tasks, including people with cataract. It becomes very prevalent when one who suffers from glare is trying to drive, especially at night, and the lights on the road appear as glare. Polaroid filters can prevent accidents and promote safer driving.
Polarizing filters block light coming in a horizontal direction, which is usually the direction of light waves that cause glare as it bounces off of bright surfaces such as water, snow or metal. Many people can benefit from polarizing filters, including skiers and people spending time in the sun, however it is recommended in the low vision field for those complaining of glare, including people who have had recently undergone eye surgery, such as cataract surgery.
Lenses with filters are available in different forms in order to use them with your glasses. There are filters available as glasses without prescription lenses. There are also filters that fit over glasses which are ideal for patients who wear prescription glasses but do not need the filter at all times. An additional benefit is that it can fit on top of different frames for people who have more than one pair of glasses. There are clip-on lenses that are easily removable, user friendly, and are customized for a specific pair of frames.
There are also filters that can be incorporated into your glasses. There are different ways of doing this depending on various factors, including the material of your lenses, if they are plastic or glass. There are different features of filters that can be ordered with your glasses, including transitional filters where the tint varies depending on the lighting conditions of your surroundings. You may have seen this with glasses that appear to be regular, but then they become darker and look like sunglasses when you step into bright sunlight conditions.
Filters, available in various colors, help regulate light and color perception based on their capacity to allow certain wavelengths to pass through while blocking others. These filters are used in eyewear for different light conditions and vision needs. Yellow and similar short-wavelength colors can enhance contrast, aiding those with conditions that affect contrast sensitivity such as cataract, glaucoma, age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa among others. The use of yellow filters, for instance, has shown significant improvement in visual abilities for individuals with retinitis pigmentosa, particularly in low illumination conditions. Polarizing filters, which block horizontally oriented light waves, can reduce glare and improve vision for those with cataracts or people who have recently undergone eye surgery. Filter lenses come in various forms to suit the wearer's needs, including non-prescription glasses, clip-ons for prescription glasses, and lenses that change tint based on surrounding light conditions.