• About Color Vision Deficiency and why Compensating Color Vision Deficiency (CVD) is Important?

• Scientific background to Colorlite color vision correcting product:

• About Color Vision Deficiency and why Compensating Color Vision Deficiency (CVD) is Important?

Vision is the most important human sensor: 90% of all information received is via vision, 5% via hearing, 2% touching, 2% tasting, 1% smelling. The loss of information due to inadequate color decoding prevents or slows down comprehension, increases reaction time and generally lowers the quality of life. 8% of men and 0,5% of women have color deficiency in the civilized word. According to the previous statistic there are 32,6 million CVD men in USA, Japan and West-Europe.

A. Normal color vision individuals are able to distinguish more than a million different shades of colors. Meanwhile an average color vision deficient person only a couple of thousands and a more serious patient only a few hundreds. This may result that a CVD person does not realize if his partner blushes or gets pale during a conversation, cannot notice if a child has fever just by his face color, cannot distinguish between ripe and unripe fruits etc. notices disadvantages in almost all areas of life compared to people with normal vision.

B. Eyes recognize and distinguish different objects based on brightness and color contrasts. CVD people are less sensitive to color contrasts, therefore they notice less details. Color printed texts, figures, charts, tables and maps can cause problems. According to our measurements, the color contrast sensitivity of CVD patients wearing Colorlite tinted lenses, can be adjusted to normal.

C. In the case of more than 100 professions CVD is a significant disability. For example doctor, dentist, hairdresser, beautician, painter, pharmacist etc. d) At childhood, CVD can have a serious negative, psychological impact. CVD children encounter problems at kindergarten, at school by painting red grass, green roofs, not being able to solve math problems etc. And can be the subjects of accompanying ridicule and jokes when not able to see their colorful books or maps or the board properly.

D. In traffic CVD people danger the life of others and their own life too. People with normal vision notice traffic lights and signs from further away. Accidents when CVDs go through a red light are quite widespread.

E. When hunting, the ability to distinguish between brown, green and khaki with high certainty is of utmost importance. Special correction lenses can be of great help in such cases.CVD men very often wear clashing colors and mismatched socks. Videogames and Internet use large number of different colors and shades. CVD patients without wearing corrective lenses get the impression that the video card in their computer is malfunctioning. Losing information is quite common for CVD people when reading red and green digits on display screens or panels, LDC screens, mobile phones.

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• Scientific background to Colorlite color vision correcting product

Human color vision

Normal human color perception can distinguish between several million different colors and the eye is capable of perceiving color in the visual wavelength range between 380 and 780 nanometers. In the human eye there are more than 6 million receptors called cones, which sense the color of the light reaching the eye. Based on the sensitivity range of their photopigments three different kinds of cones can be identified. Their names are Protos or L cone, (sensitive to the red colors: Long wavelengths) Deuteros or M cone (sensitive to the green colors: Medium wavelengths) and Tritos or S cone (sensitive to the blue colors: Short wavelengths). The figure below shows the sensitivity functions of these receptors.

Figure 1. Normal receptor sensitivity functions in arbitrary units over wavelength

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Inherited CVD

Color vision ability is essentially the ability of the observer to identify the colors (color identification) and the ability to distinguish between slightly different colors (color discrimination). Normal color vision is defined as the color vision ability of an "average" observer. Color vision deficiency occurs when one or more of the cone's sensitivity functions differ significantly from the above shown normal ones. This results in the alteration (reduction) of color identification and color discrimination ability. Based on their genetic origin and characteristics several types of color vision deficiency can be distinguished. The most common ones occur in the red and/or green region (Protanomaly or Deuteranomaly), much more seldom the blue region is defective (Tritanomaly) and only in extremely rare occasions all the three receptors are damaged or missing (Achromatopsy).
The red-green color vision deficiency is inherited genetically with the "X" chromosomes; consequently it is much more common among males than females. Women have two X-chromosomes and if one of them carries the color normal genetic information it suppresses the defective information in the other one. Men do not have this duplication; therefore if a man inherits a defective X chromosome from his mother (who is most likely not color vision deficient) he is going to be CVD. Approximately 8 % of Caucasian men and 0.4-0.5 % of women are red-green color vision deficient. Inherited blue color vision deficiency is extremely rare, approximately 0.05%.
For many years it was taught that color vision deficient receptors differ from normal ones due to their insufficient sensitivity. However, recent scientific publications are describing color vision deficiency as a consequence of the change in the sensitivity range of the receptors ('parallel shift'). The Colorlite color vision correction method is based on this theory.

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Color vision enhancement

Colorlite has designed and manufactures lenses with a special coating, which is designed on such way that enhances the individual's color vision. The correction can be applied for each type of red-green color vision deficiencies, even in the most severe cases of Protanopy (total lack of red cones) and Deuteranopy (total lack of green cones), however, in their cases only color discrimination can be improved by transferring color information to brightness information.
Figure 2 below shows the cone sensitivity functions of a Deuteranomalous subject (someone whose Middle wavelength sensing receptor sensitivity is shifted towards the Long wavelengths.) Due to the shift, the difference between the L and M sensitivity functions decreases; therefore the subject has difficulty in differentiating between green and yellow shades.

Figure 2. L, M, and S cone sensitivity functions of a normal and a Deuteranomalous subject. L and S cones fully overlap; the difference is in the M cone sensitivity.

To compensate for this defect a specially designed filter can be used. The requirement for this filter is to shift the Middle wavelength intensity of the light reaching the eye in such a way, that the CVD receptors sensing the shifted spectrum send the same information to the visual nervous system, as the normal receptors would do sensing the unaltered incoming light. The filter has to be effective in the middle wavelength area where the deficiency is, and cause the least possible interference in the Short and Long wavelength range where the receptors of the CVD subject are normal.
A suitable filter characteristic for the case shown on Figure 2 is shown in Figure 3.

Figure 3. A filter suitable for the CVD case shown in Figure 1.

To compensate for this defect a specially designed filter can be used. The requirement for this filter is to shift the Due to the effect of the filter on the light reaching the eye the cones are excited on such way that the information sent towards the visual nervous system is identical to the one as if the cone sensitivities were as shown in Figure 4. Thus, although the eye itself has not been altered and the Medium wavelength receptor sensitivity function remains shifted, the visual information becomes much closer to normal color vision than it was before. When considering the adaptation ability of the individual cones (e.g. the ability of the receptors to increase their sensitivity when there is low incoming signal and decrease their sensitivity when the incoming signal is high) from the color vision prospective this can be interpreted as if the sensitivity function of the receptors were really shifted.

Figure 4. Effect of the filter shown in Figure 3.

Figure 4 shows clearly that the filter shifted the defective Medium wavelength cone sensitivity very close to the normal one, left the Short wavelength sensitivity function untouched and caused a very small deviation in the Long wavelength sensitivities. The subject's color vision abilities have been restored very close to the normal.

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Color vision testing and diagnosis of CVD

The traditional diagnostic tests, including different pseudo-isochromatic tests (Ishihara, Dvorin, Velhagen, etc.), yarn test, lantern test, etc. can only detect whether a subject is red-green color vision deficient or not. The type and, to some degree, the severity of the deficiency can be measured using an equipment called anomaloscope. Nowadays, the most advanced anomaloscopes are capable of detecting not only red-green, but blue color vision deficiency as well.
Colorlite's color vision test ("CVTest") book not only distinguishes between the red-green and other, rare types of color vision deficiency, but also provides a quantitative estimate on the severity of red-green color vision deficiency. Basically the Colorlite Test Book assesses the shift of the defective receptor sensitivity function relative to the normal one in nanometers. The application of the parallel shift theory allows for not only a more accurate diagnosis of CVD, but at the same time permits to suggest the best corrective lens. The easy-to-use CVTest simply recommends lenses for CVD subjects, classified by our thorough research of several years and it measures the efficiency and the level of improvement.

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