Filtered Contact Lens
Prescribing the Right Filter for Achromatopsia
"I believe that, if color information were suddenly to become available to my eyes, it would so bewilder me that I would probably have great difficulties adjusting to it. However, I would like very much to have better visual acuity and to be less bothered by strong light….”
- Achromat Network Member
Red Central - NARS Red/Black - Amber/Brown - Magenta
In our low vision practice, achromatic soft contact lenses with custom designed filters have revolutionized our ability to help achromatopsia patients control the overwhelming aversion to the light. Except in children too young to wear contacts, it is frequently our first step in low vision rehabilitation. Early attempts to fit rod monochromats with solid red hard contact lenses decades ago were limited by the comfort and size of the hard and gas perm contact lenses. Today, the achromat contact lenses are soft contact lenses in custom filter colors that provide excellent comfort and allow customization to precisely fit the light sensitivity need of each patient. Each patient must be custom fit to assure the correct level of darkness, the best color of filter and the size of the filtered area.
Above we see a young lady with rod monochromatism. In the picture on the left side is without her filtered contact lenses. Notice the severe squinting required to reduce the light entering her eyes. In the picture on the right side, she is wearing her red central contact lenses, and can open her eyes naturally.
When she wears the red central contact lenses, she requires no additional tinting inside and can now wear a normal appearing sunglasses outside, which in this case a grey filter. In the evening, the contact lenses can be removed.
Because our brain helps us adapt to differences in brightness, we often fail to appreciate the great difference in brightness from outside on a sunny day to inside a normal room. The human visual system can function over a tremendous range of brightness levels.
The chart below shows the range of brightness within which our visual system can normally function.
Without filters, achromats may function comfortable in only the lowest 3 to 4 areas above. The difference in brightness from an inside dimly lighted home to outside bright sunlight in the summer can vary by 2500 times. Even the difference from inside illumination in a bright classroom or office to outside sun on a bright day may vary by 350 times. Thus we must deal with both the high and the low light that an achromat routinely encounters. No any single filter is able to handle all levels of lighting. Sunwear will be added over the contact lenses outside, and in the evening, many patients remove the filtered contact lenses, or switch to clear lenses.
We do not fit the lens to totally eliminate the outside glare. This would create too dark a lens when inside. Rather, we fit the contact lens to resolve as fully as possible the inside light issues without being too dark in normally encountered areas of less light. This also will dramatically reduce the outside glare, but the patient will then be able to wear a more normal moderate amber/brown sun filter to control the now much reduced glare outside. Fitting too dark a lens was common, when hard lenses limited the options. Today it is easy to adjust the filter to fit the patient.
Every achromat is different. Thus, the doctor and patient must evaluate different filtered contact lenses in real world lighting settings inside and outside. After the color of the filter is determined (red, red-black dye, amber/brown, magenta and green) filters, we then determine the density of the filter, lighter or darker, based on the testing with the trial contact lenses. As shown on the photo to the right, we design different sizes for the filtered portion to customize the fit to the patient.
The results are usually very dramatic, even patients who initially report that they are only mildly light sensitive, suddenly report seeing better. It is important to test the patient's near vision to assure the filter does not interfer with reading.
Filtered Contact Lenses
To learn more about how filtered contact lenses may help someone with achromatopsia. Download the PDF file “What to Expect from Filtered Contact Lenses for Achromatopsia.” This article helps provide a better understanding of the benefits of filtered contact lenses for many achromats.
The NARS: Black - Red Contact Lens
The NARS Filter Contact Lenses: This combination (black–red dyes) provides very dark filtering with a very cosmetic appearance. Notice the patient does not need to squint in the light. You also do not see a red appearance to the lens.
The Red Central Soft Contact Lens
Red Central Medium Filter Soft Contact Lens: Note that the contact lens does not appear red until the penlight is deliberately flashed on it. This patient wears a lens with a red filter that covers the entire cornea. This lens in made in different darkness levels of the red. The example below is a medium red.
The Amber - Brown Soft Contact Lens
In fitting patients with blue eyes, red lenses may not provide the best cosmetic appearance. We can convert the blue-eyed patient to brown eyes with an amber/brown filtered contact lens. Here for demonstration purposes, we have removed her left contact lens to show her underlying blue eyes. This lens is especially helpful in blue colored eyes. It is made in different levels of darkness. The lens below is a medium filter.
The Magenta BCM Soft Contact Lens
Blue cone monochromat patients maintain function of the blue cones. Using a red filter would inhibit the blue light. However a magenta filter made from the mixing of both red and blue dyes is very effective. The red component of the filter protects rod function while the blue portion allows the blue cones to still function.
The B30 Contact Lenses
The B30 Contact lenses provide better cosmetic appearance than the red central contact lenses. It appears dark brown on the patient’s eyes. Many rod monochromats find it a good balance of cosmetics and vision.
The B60 Contact Lenses
The B60 contact lenses are ultra-dark contact lenses, which appear dark brown on the patient’s eyes. They are often very effective for younger patients, who are often much more light sensitive. The more neutral color does not reduce residual color vision in incomplete rod monochromats
Designing Soft Contact Lenses for Achromats
Selection of Color: Red is usually very effective for rod monochromats while magenta can be helpful in blue cone monochromats. The NARS, red-black dye form, is particularly helpful in those with the most severe light sensitivity as it creates a very dark filter. The amber/brown filters are only slightly less effective, but offer much better cosmetics. We simply change the patient to the appearance of brown eyes. The B30 and B60 These have a better cosmetic appearance than a red lens partially covering a blue eye. They are often a good cosmetic choice for women with blue eyes.
Density of the Tint: Density or darkness of the filter is determined by the time of dye exposure. It is determined by trial testing with the patient in real world activities in different levels of light, both inside and outside.
Size of the Tinted Area: We may elect to make the filtered area slightly larger than the pupil of the eye to create the appearance of a dark pupil or we may cover the entire cornea to allow complete coverage of the iris or colored portion of the eye. The filtered area must be large enough to prevent bleeding of light through as the pupil dilates in different lighting conditions. In deep-set eyes, the red lens will appear dark and look like a normal pupil. In a blue colored eye, a brown filter at a size to color the entire colored portion of the eye may be used.
The cosmetic benefits of filtered contact lenses are great. It is life changing for many patients. There is not one filter color, size and density. The contacts must be tested by the patient with trial diagnostic contact lenses and custom designed to meet the needs of each achromat. Filtered contacts do not eliminate the need to wear a sunglass outside.
The patient will no longer need to wear dark lenses inside and only wear a moderate and more cosmetic sunglass filter outside.
Eliminating the dark lenses when inside has a great cosmetic benefit in all social interactions. Once glare is controlled, low vision aids can be much more effective.