Study finds 24% of Spanish drivers have some vision problem

Feb 5 2011

One in four Spanish drivers has a vision problem that affects their driving ability. This is the finding of a study commissioned by the association Visión y Vida in collaboration with the RACC to Aurora Torrents and Jaume Escofet, professors at EUOOT (UPC-Barcelona Tech). The aim of the study is to provide objective information on the eyesight of Spanish drivers.

Ninety percent of the information drivers depend on to make decisions is visual. Assessing the eyesight of Spanish drivers is therefore an essential step to improve road safety and reduce the accident rate on the country's highways. To this end, the public interest association Visión y Vida commissioned the Terrassa College of Optics and Optometry (EUOOT) of the Universitat Politècnica de Catalunya (UPC) to conduct a study aimed at providing public authorities and society with objective, evidence-based information on the eyesight of Spanish drivers. UPC researchers Aurora Torrents and Jaume Escofet, both professors at the EUOOT, are the authors of the study, which was carried out in collaboration with the Royal Automobile Club of Catalonia (RACC).

Main results of the study

• 24% of the drivers in the sample (6 million Spanish drivers) have some vision problem. 
• 58.4% of the drivers in the sample use glasses with an incorrect prescription.
• 62% of the drivers in the sample have poor contrast sensitivity.
• 36.9% of the elderly drivers in the sample have color discrimination problems.
• The vision examinations drivers must pass to obtain or renew their licenses are not very rigorous or thorough. 
• The application of license restrictions based on the visual abilities of drivers would reduce the number of accidents.

Improve testing of visual abilities

One of the key outcomes of the study is a recommendation that public authorities make changes to vision testing, which is carried out within the framework of psychological and physical aptitude tests required to obtain a driver's license. According to the authors of the study, there are a number of visual abilities that can be very precisely measured. In these cases, the sponsors of the study recommend that regulations should be more explicit in terms of both testing specifications and reference values used. In current tests, for example, no value is specified for a normal visual field. It was also found that most of the centers where vision testing is performed do not have an instrument as basic as a campimeter, and that when one is available it is not used because of the speed with which the entire medical examination is performed.

Neither do current regulations define what is meant by the ability to recover from glare or specify a minimum reference value. Similarly, current regulations do not establish a value for contrast sensitivity, though the study indicates that measuring this parameter provides a better assessment of the quality of the visual system. Another important factor is stereoacuity, the ability to detect differences in distance, which is what enables us to see in three dimensions. Poor stereoacuity adversely affects driving ability in dynamic situations. Current regulations do not provide that measurement of this visual ability be taken into account. The levels of stereoacuity observed in the study were very poor. This parameter can be measured easily and directly.

Existing regulations do not provide for testing of near vision despite the fact that drivers suffering from presbyopia (60% of the population) have difficulty seeing some of the information displayed on a car's instrument panel. Affected drivers have to move their heads back to focus properly, which takes their attention off the road and can slow reaction time by vital seconds.

Color vision deficiencies are not covered by existing regulations. Eight percent of the male population suffers from color blindness. Drivers affected by this condition associate the colors of traffic lights with their position but may become confused at night. The tests used to assess this condition are simple and practically cost-free. The study raises the possibility of using a different geometrical shape for each traffic light color to facilitate their identification by all drivers.

Finally, the study found that the visual abilities of elderly drivers fall short of those of the rest of the population. The report concludes that current reference values for these drivers are too lax and should be raised.

Restrictions linked to visual abilities

Existing regulations envisage a series of harmonized codes—both national and at the level of Spain's autonomous communities—to be indicated on driver's licenses. These codes are explicit with respect to the use of glasses and contact lenses, but it is not usual to find codes indicating other restrictions based on a driver's abilities. For example, such restrictions could indicate that a driver can only operate a vehicle in urban areas, during the day, or subject to a specified maximum speed. The study therefore recommends greater application of the restrictive measures that are provided for in existing regulations for certain groups of drivers.

Over a thousand drivers tested

The study was conducted in May and July of 2010 on a sample of 1027 drivers. A series of tests were performed on the participants to measure visual acuity, stereoacuity, contrast sensitivity, glare sensitivity, color perception, and visual field. The tests were performed using an OPTEC 5000 PG Vision Tester at RACC stands set up at a number of shopping centers in Barcelona, the Madrid Ecological Vehicles Show, the Barcelona Harley Days event, schools on the UPC Campus in Terrassa, and the Anna Murià Seniors Center in Terrassa.

TECHNICAL DETAILS

• Population: Spanish drivers
• Sample size: 1027 individuals
• Sampling error: For a confidence level of 95.5% and p = q, the margin of error is less than 3.16% (simple random sampling)
• Method: Questionnaire and measurement of visual parameters
• Date conducted: May - September 2010

The visual abilities of Spanish drivers

Binocular visual acuity at distance
Four percent of the sample has a value of less than 0.5, which is the cut-off value to obtain or renew a driver's license; and 58.4% of the sample has binocular visual acuity at distance of 0.8% or less, which indicates that they are probably using glasses with an incorrect prescription. According to the experts, this is cause for concern.

Stereoacuity
Six percent of the drivers analyzed in the sample do not have three-dimensional vision. The lack of stereoacuity makes driving more difficult in dynamic situations.

Contrast sensitivity
This parameter predicts the quality of vision individuals experience in their daily lives. Only 37% of the sample could distinguish the lowest-contrast letters. This demonstrates that for a high percentage of drivers contrast sensitivity is not optimal.

Glare sensitivity
A considerable increase in glare sensitivity is observed in elderly drivers.

Color perception
The study found that 6.4% of the drivers in the sample suffer from color blindness. In the case of elderly drivers, the proportion rises to 36.9%. The authors of the study suspect that this increase may be due to certain age-related pathologies, medications taken, or possibly a degree of cognitive decline.

Visual field
In 4% of the individuals analyzed the extension of the visual field is less than 85°. The authors of the study warn that this result should be treated with caution because the test only examined the maximum horizontal extension of the visual field: it did not include an analysis of the entire visual field.

Source: VISIÓN Y VIDA