Colourblindness

To help you fully understand colourblindness you need to be aware of what we call "CVD", hereditary factors and also understand the technical side of how the lenses work.

What is CVD

CVD is called ‘colour blindness’ by mistake. In actual fact the term describes a number of problems that people may have with their colour vision. Abnormal colour vision may vary from not being able to distinguish between certain shades of colour to not being able to identify any colour.

Vision is truly an amazing process. Receptors in the Retina at the back of the eye send signals to the brain via the Optic Nerve to be interpreted as sight. There are two types of receptors - Rods and Cones. Rods work best in low light levels, found in the outer regions of the Retina and help with our night and side vision. They are not colour sensitive. There are three types of Cones responsible for the colour signals, each containing a different pigment, and they are activated when the pigments in them absorb light. They are concentrated mainly in the small area called the Macula, which also gives us our central, detailed vision. Each has a Latin name relating to the order of wavelength to which they respond.

Protos: most receptive to the longer wavelengths (L cones) Reddish colours.

Deuterous: most receptive to medium wavelengths (M cones) Greenish colours.

Tritos: most receptive to shorter wavelengths (S cones) Bluish colours.

The different kinds of CVD result from one or more of the different cone systems either not functioning at all, or functioning in an unusual way. The most common forms of CVD result from problems with either the middle or long wavelength sensitive cone systems and involve difficulties in discriminating the reds and greens and all the various shades of these colours.

Protanomaly: Mild deficiency in the sensitivity of the L cones. Being less sensitive to red light which will cause a darkening of reds to appear brown or even black in some cases.

Protanopia:: Total lack of the L cones. Distinguishing shades of colours in the green-yellow-red section of the spectrum is greatly reduced.

Deuteranomaly: A mild deficiency in the sensitivity of M cones. The medium wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum.

Tritanomaly: Mild deficiency is the sensitivity of the S cones. Blues and yellows will be confused.

Trianopia: Total lack of the S cones causing confusion in the blue-yellow section of the spectrum.

Who does CVD affect?
A general consensus is 8% of the male population and 0.5% of females have some form of CVD. This generally runs in families, being an inherited condition. Less commonly, it can be an acquired defect through conditions such as Diabetes, Cataracts or Optic Neuritis or can be drug induced.

Our testing procedure involves first determining the type and degree of deficiency. We do this with various methods including computer based tests that each person will perform themselves. The time taken will vary but we always allow at least pne hour, since after the correct lens is determined the person will wear the lenses to see how they change and enhance their world of colours. We also encourage each person to bring along a family member or someone close to them to observe the test, as this is the defining moment when true colours are seen for the first time. Many questions can arise and it is a great time to share.

After the analysis procedure, if you are happy with the results, the lenses will be ordered for you. The lenses are available in non prescription only. For prescription spectacle wearers, a custom fitting clip-on is best and can be chosen with one of our fully trained Optical Dispensers.

The lenses are by far the best quality lenses to treat CVD. They give a truer perception of the colours and are very durable.

Hereditary Chart

Colour Vision Deficency can be either an inherited or an acquired condition.

8% of the male population and 0.5% of the female population suffer from inherited CVD. The genetic heritage is linked to a defect in the X chromosome and usually affects every second generation of a family. Diabetes, alcoholism or certain medicines may cause acquired CVD.

Technical Features

This chart shows how the lenses change the spectrum of light which stimulates the cones to begin releasing the chemicals that produce the electrical signal that travels along the Optic Nerve up to the Occipital Cortex in the brain, which is then interpreted as vision, specifically colour vision.

The lenses were seven years in the research and development stage.  They are manufactured in special vacuum coating chambers. Several layers are applied in the correct sequence, which is a patented process. Each layer must be perfect before the the next layer is applied and so if one layer does not adhere exactly then the whole process has to begin again with new lenses. Each batch is thoroughly inspected and must pass strict quality controls before being allowed out of the factory.

As the process is complex, only piano or non prescription lenses are produced and so for spectacle wearers the lenses are put into clip-ons over the prescription spectacles.