Visual disorders and driving. Color perception
The useful visual field is known as the “attentional field”, which is the size of the field controlled by the gaze when the central and peripheral fields are stimulated with two stimuli.
At 30 km/hour, visual attention is focused on a region of 150 meter; at 100 km/hour, it is focused on a region of 570 meters.
It has been shown that drivers with a reduction of 40% or greater in attentional field have a six times higher risk of suffering an accident than those with a normal attentional field.
Color perception and color blindness
The ability to perceive color in a normal eye decreases with low levels of illumination. Total color blindness or achromatopsia is very rare; only the changes between black and white are distinguished (shades of gray).
Impaired color vision from birth or congenital dyschromatopsia affects nearly 8% of men, but, because it is an X-linked genetic recessive defect, very few women have this condition.
Dichromasy or the ability to see only two colors (yellow and blue or red and green) is the most common form.
Lack of color perception is known as color blindness. Three types of color blindness are distinguished: protanopia or absolute deficiency of red cones, deuteranopia or absolute deficiency of green cones, and tritanopia or absolute deficiency of blue cones, which is extremely rare.
Total color blindness is rare, with protanopia being much more common. Drivers with protanopia have difficulty distinguishing the tail and brake lights.
Deuteranomaly or “green weakness” and protanomaly or “red weakness” are more common.
In Europe, approximately 8% of men and 2% of women are color-blind. The majority of affected individuals are unaware of their inability to distinguish colors well, which manifests mainly at dusk or in fog.
Partially color-blind persons do not distinguish between colors, but perceive differences in their luminosity, which allows them to distinguish between traffic signals, provided there is sufficient illumination.
The driver knows that red is above and green is below on traffic lights, but when colors appear out of context, he/she may confuse them and make mistakes. This situation can be worsened by the use of sunglasses with lenses of the wrong color.
Acquired dyschromatopsia may result from optic neuropathies or occur transiently as a result of the effect of diverse drugs such as acetylsalicylic acid, digitalis preparations, thiazide diuretics, ethambutol, phenacetin, certain antibiotics, toxins and drugs such as cannabis.
Noise and prolonged vibrations may alter color sensitivity.
The vehicle colors that are most visible to the human eye are white, ocher and light ivory (68 88% visibility). Gray, brown and green are less visible (19-28% visibility). The least visible colors are red, black and dark blue (4-10% visibility).
At night, red reflecting signs are the ones that best alert the driver to the presence of obstacles.
- It should be recommended that new compensation strategies are learnt in drivers with a reduction in the “attention field”, very frequent in the elderly that in addition are not aware of their visual vision.
- Health professionals should play an essential role in the prevention of the accident rate in people with visual disturbances.
- The examination of the chromatic sense is very important and we should warn the driver of its effect, so that he adopts precautions, particularly in case of fog, rain and lack of light.
- The patient should be warned of thee drugs that can cause dyschromatopsia,(*) so that he tries to drive with light and good climatological conditions.
- When we purchase a vehicle it is preferable that we choose the white, ochre, and clear ivory color, for the safety of been better seen at night.
- We should recommend drivers with color perception disorders to use sunglasses with the appropriate color for each case.
- The driver with chromatic sense disorders should drive with light, avoiding night driving. If he should travel at night, it is advisable that he does it in the seat of companion for his safety and that of others.
- It should be recommended that new compensation strategies are learn in drivers with visual field reduction, very often in elderly people that have lost functions progressively and are not aware of it.
(*)Variety of color blindness where only two of them are distinguished.