Effect of Protanopia on the Brightness Perception of Brake Lights

Protanopia is an x-chromosomal inherited cone pigment disorder that related to the red cone,i.e. the L-cone function completely fails. The prevalence of protanopia in the male population is 1%. An incomplete impairment of the L-cone is called protanomaly. The prevalence here is also in 1% of the male population.

In comparison to persons with normal vision red objects appear darker for persons with missing or functionally limited L-cones. This is particularly critical in road traffic, where red is used as a signal colour, for example in traffic lights or brake lights is used.

The scientific questions that need to be investigated are as follows:

1. At which contrast threshold (relative brightness) does a proband with protanopia recognize a brake light compared to a normal person?
2. If the luminance determined is above the contrast threshold, what influence does the excess of the contrast or the determined luminance have on the reaction time?
3. Are there differences with regard to the technology used in the brake light (incandescent lamp or LED)?

For this purpose, a representative set of combination rear lamps, focusing on stoplight, taillight (and of the elevated brake light) in a static situation is created. The test setup is based on a driving pursuit scenario. The test person is positioned at a relevant distance to the combination of rear lamps.

To determine the threshold contrast, an algorithm is developed to control the relative brightness of the brake lights and integrated into the test sequence control. In addition, a method for automated determining of the related reaction time is implemented.

Two taillight technologies (incandescent lamp and LED) are examined at both ambient brightness levels: (i) "bright", i.e. photopic luminance level (Lu >> 10 cd/m2) and (ii) "dark", i.e. mesopic luminance level (Lu \< 10 cd/m2).

A comprehensive ophthalmological/optical examination (including visual acuity, ocular alignment, ocular motility, assessment of the leading eye, testing of the efferent and afferent pupillary system and biomicroscopic inspection of the anterior and posterior segments of the eye) is carried out. Comprehensive colour vision testing it performed with the HMC anomaloscope, Oculus Inc., Dutenhofen/FRG, including assessment of the loss of brightness sensation during anomaloscopic exam with max. red. stimulus . In addition, standardized semi-automated kinetic perimetry (SKP) along the horizontal meridian with an automated perimeter (Octopus 900, Haag-Streit Inc., Koeniz/CH) is performed. The ratio of the horizontal extent ("diameter") obtained with both, red vs. white stimuli, is measured and taken as a clinical parameter for quantifying the magnitude of the individual "protan colour vision deficiency".

To illustrate the worst-case scenario, this study is limited to protanopic patients. It is intended as a pure comparative study between a "protanopic" patient group and a "normal vision" control group. The protanopic test subjects and the control subjects are matched with regard to gender and age.

This study is carried out in a "within-subject design", i.e. all test persons go through all situations. In order to minimize sequence effects, the related test conditions are randomized.