The question of driving with low vision has recently become a very contentious issue. Many people argue that, since the 9/11 Commission Report of 2004 mandated the Secretary of Homeland Security to "issue standards for drivers' licenses" as part of a more general terrorist travel surveillance and screening effort, a golden opportunity had presented itself for introducing uniformity and equity into licencing standards.

Why are feelings running so high? Critics of the DMV point to discrimination in the system against driving with low vision. They have plenty of ammunition to support their case as the visual acuity and peripheral vision requirements vary greatly from state to state in the United States.

Let's compare two southern states: Alabama and Georgia. In Alabama, minimum visual acuity without correction is set at 20/40, and peripheral vision at 110?. However, along with 15 other U.S states you cannot use bifocals for driving to help read street signs and avoid obstacles.

In Georgia, by contrast, you are allowed to wear bioptics, but the field of view requirement is more stringent at 140? while the minimum visual acuity figure is more relaxed at 20/60.

Such inconsistencies fuel the debate calling for more latitude in interpreting whether a driver with low vision is a fit driver. There is no consensus about drivers with moderate visual impairments for example, and, in some states, visual acuity is the only yardstick by which safe driving is measured.

Current research suggests that visual acuity alone is not a valid predictor of driving ability and safety: quite the opposite, in fact. Much weight in this research has been given to factors unconnected with vision, including:

* aggressive and impulsive personality traits.

* poor concentration, possibly as a result of substance abuse or medication taken.

* age factors, especially teenagers and older drivers over the age of 75.

* compromised health with respect to hearing loss, seizures and orthopaedic impairments.

In relation to drivers with compromised health, a study conducted a decade ago on 669 Bioptic drivers in California found that accident rates for these drivers were up to two times higher than for the Bioptic driver group. The study's conclusions found Bioptic drivers did not carry an unacceptably high risk, but advocated the appropriate use of license restrictions. These included: limiting a low vision driver to travelling in daylight hours only; using a specially adapted vehicle, and more frequent testing by the licensing agency.

On the other side of the argument, though, there are genuine concerns expressed about the use of Bioptic lenses for driving with low vision. The Bioptic telescope creates a small visual field causing a hazardous blind spot. Problems are also said to arise with speed blur, when using the Bioptic with mirrors and with depth perception. This is similar to the apparent difference in the position of an object when you look through the viewfinder and the lens of a camera.

The solution seems to lie in a flexible, driver-centered approach where there is a collaborative effort between the low vision driver, the licensing agency and the eye specialist. In some states, prior to a final test taking place, drivers with visual impairments are offered training to improve their driving skills and learn compensation techniques.

In this way, some states sanction licensure for individuals with visual acuities up to, but not including, 20/200. However, they must have demonstrated a high degree of skill and ability in a road test. To obtain their license, drivers with low vision will have demonstrated all-round ability in:

* Maximizing eye movement instead of head movement, thereby reducing response time.

* Rapidly locating stationary objects while static.

* Rapidly locating moving objects while static.

* Rapidly locating moving objects while on the move.

* Developing precise vision perceptual skills enabling rapid evaluation of the environment.

This appears to be a good way forward, but is it always necessary for drivers with low vision to give up driving at night? Two principal reasons are given for restricting low vision drivers to daytime driving only: glare from oncoming vehicles, and a much reduced ability to see ahead. It should not be a surprising fact that over 60s perceive just one third of the light that a 20 year old perceives.

Infrared night vision systems in vehicles have been proposed as a good, partial solution to the problem of night-time driving for bioptic wearers. An infrared beam lights up the objects ahead to a distance of 500ft. compared to 130ft. for conventional headlights, and the detected objects are displayed on the lower part of the windshield. No movement of the head nor averting the eyes from the road is involved.

To date, though, progress has been very slow and patchy. Some top-of-the-range models have been fitted with the infrared night view system, but on many popular models no such option is offered.

Progress also has to be made in moving away from strict, general parameters which allow all applicants with, say, 20/100 visual acuity to drive. Non-visual factors, as we have seen, also come into play. Best practice would involve the possibility of allowing a suitable individual with 20/200 vision to drive, yet denying a driving license to someone with 20/80 visual acuity. Everything is relative, as they say.