Vision and driving: what really matters behind the wheel

‘Can I still drive?’, and its variant after surgery, ‘when can I get back behind the wheel?’. These are two of the most frequent questions in consultation, and two of the hardest to answer in a single sentence. Driving does not depend on a figure read off an acuity chart: it draws on a whole set of visual functions, most of which are never measured in a routine examination. Here is what the studies actually establish, what they do not settle, and where the limits of what an ophthalmologist can say lie.

UNDERSTANDING

Does 10/10 vision mean you drive well?

No, and this is the most robust finding in the whole field. An Australian study put 560 drivers aged 65 to 96 through a real fifty-minute on-road driving test, assessed by an occupational therapist blind to their visual and cognitive status. Twelve per cent were classed as ‘at-risk drivers’. Each acuity line lost increased the odds of falling into this group, but the acuity threshold usually used for screening picked up only 3% of these unsafe drivers.

The wider evidence points the same way. A meta-analysis of 101 studies covering 778,052 drivers does find an association between reduced acuity and accidents, but its estimate is the lowest of the three: a relative risk of 1.21 (95% confidence interval: 1.02 to 1.43), against 1.40 for contrast sensitivity and 1.51 for visual field. A systematic review of 48 studies, meanwhile, concludes there is no evidence of excess risk with mild acuity impairment.

A recent review sums up the paradox: almost everywhere in the world, licensing relies essentially on acuity thresholds, while safe driving depends on several functions working together — central and peripheral vision, contrast sensitivity, perception of movement and depth, and visual processing speed. That does not make acuity useless: it is still needed to read a road sign. It is simply very insufficient on its own.

VISUAL FIELD

Visual field: the deficit most closely linked to accidents

This is the function whose link with accidents is best established. An Australian study cross-matched the visual fields of 31,296 people over 50 with accident records over twenty-nine years: 4,307 drivers were involved in 5,537 accidents. Binocular visual field impairment, whatever its severity or location, increased the odds of an accident by 84% (odds ratio 1.84; 1.71 to 1.97). For severe impairment, the quadrant-by-quadrant figures ranged from 1.89 to 1.98.

The meta-analysis of 101 studies gives visual field the highest relative risk of the three measures — 1.51 (1.23 to 1.85) — but it does not rank them: each estimate rests on only four or five studies, and their confidence intervals overlap. And the most cautious systematic review in the field, which declines to draw conclusions on most eye diseases, accepts only one association as backed by good-quality studies: that of binocular field. Peripheral impairment affects 13% of people over 65, and shows up first as difficulty keeping to a lane.

Hemianopia after a stroke is the extreme case, and it holds a surprise. In simulator testing, affected people miss more events in their blind hemifield than in the seeing one — 34.6% against 10.4%. Yet in a Swedish cohort of 153 drivers whose licence had been withdrawn for this reason, 65% passed a standardised simulator test, and of the 93 who got their licence back, none had an accident over the following three to six years.

GLAUCOMA

Glaucoma: a real risk, but not a life sentence

The glaucoma erodes peripheral visual field without the patient noticing, which makes it the ideal candidate for this question. A US study of 2,000 drivers aged 70 and over compared at-fault accidents over the previous five years: the 206 people with glaucoma had a rate 1.65 times higher (1.20 to 2.28). Among them, the excess risk was linked to visual field impairment — 2.11 times higher with a severe deficit, with a wide interval of 1.09 to 4.09 — and not to acuity or contrast, for which no association was found.

Real-world observations point the same way. A systematic review of 23 studies finds that, with a moderate to severe field deficit, reaction times to hazards lengthen, lane-keeping worsens and night-time discomfort increases. In simulator testing, braking delay went from 2.39 seconds in controls to 3.39 seconds in 52 patients with glaucoma. A hazard-perception test shows an average delay of 0.73 seconds in drivers with eye disease — around sixteen extra metres of stopping distance at 80 km/h.

Yet the other side of the picture must be held too. In the meta-analysis of 101 studies, the association between glaucoma and accidents does not hold up: a relative risk of 1.27, but an interval running from 0.67 to 2.42, with extreme heterogeneity between studies. A French cohort of 12,460 drivers even finds that glaucoma comes with reduced mileage and avoidance of certain situations, without any increase in accidents. In other words: the severity of the deficit matters, the diagnosis alone says nothing.

CONTRAST

Contrast sensitivity: the function nobody measures

Contrast sensitivity is the ability to tell a shape from its background when their brightness is similar: a dark car on a wet road, a pedestrian in a grey coat at dusk. It declines with age, early cataract and glaucoma, often well before acuity changes. A study comparing seven visual parameters in 151 patients with glaucoma finds that contrast measures are the ones that best explain reported difficulty and daily physical activity — driving cessation, for its part, is mainly tied to acuity — and that they are rarely carried out in practice.

Real-world driving data bear this out. In a US study in which 854 drivers over 60 had their vehicles fitted with cameras and sensors for one to two years, contrast sensitivity measured under mesopic lighting — twilight-level light — was associated with at-fault accidents, with a rate ratio of 1.50 (1.16 to 1.93). The same measure taken in full light, by contrast, was not associated with any increase in risk. In another, much smaller instrumented study — seventy-one drivers followed for two weeks — each 0.1 log-unit gain in sensitivity came with 30% fewer critical events: hard braking, sharp acceleration and abrupt turns, not accidents.

In a night-time simulator, in fifteen older subjects free of eye disease, contrast sensitivity predicted the distance at which an obstacle was detected, whereas conventional high-contrast acuity did not. The practical consequence is immediate: the patient who says ‘I don’t see as well for driving’ despite excellent acuity is not making it up. They are describing a function the standard consultation never looked at.

NIGHT DRIVING

Night-time: headlights and halos

Night driving is the most demanding situation, and the deadliest: for the same distance travelled, mortality is higher than by day, particularly for collisions involving pedestrians and cyclists, whose reduced visibility is the main factor implicated. Under the mesopic lighting of the road at night, every visual function deteriorates, and this deterioration is more pronounced with age and with eye disease.

Glare adds its own toll. On a closed circuit, at night, twenty-six older drivers who complained of night-time difficulties saw their driving score fall in the presence of intermittent headlights: pedestrian detection dropped by 38%. Performance was best explained by motion sensitivity and by acuity measured under mesopic lighting, not by conventional full-light acuity.

What feels like a ‘veil’ of light is not necessarily what people assume. In one dedicated experiment, straylight measured with a specialised device was a poor predictor of the distance at which obstacles were recognised, whereas contrast sensitivity measured in the presence of glare predicted it strongly.

CATARACT

Cataract: what surgery changes for driving

Let’s start with what patients experience. Among 99 drivers over 50 with cataract in both eyes, 85.9% reported difficulty driving at night and 73.7% in the rain. The discomfort score correlated with contrast sensitivity, not with visual acuity. This is exactly the pattern described above: the complaint comes before the figure.

And surgery? This is where the evidence is most encouraging in the whole article. In the meta-analysis of 101 studies, cataract surgery is the only intervention associated with a reduction in accident risk, with the risk almost halved: 0.55 (0.34 to 0.92). The heterogeneity between the three studies involved, however, argues for reading the direction of the effect rather than its exact magnitude.

A prospective simulator study supplies the missing detail. Forty-four drivers over 55 with bilateral cataract were assessed before any surgery, after surgery on the first eye, then after surgery on the second. The rate of accidents and near-misses fell by 36% after the first eye, then by 47% after the second, relative to the starting point. The second eye therefore brings a gain of its own.

AFTER SURGERY

‘When can I get back behind the wheel?’

Let’s start with a necessary piece of honesty: none of the studies gathered for this article sets a delay in days after eye surgery. It is not a universal figure, it is an individual judgement, and it belongs to the surgeon who operated — we set out the concrete criteria on our page about driving after cataract surgery. What can be assessed are the conditions: distance vision recovered and stable, light sensitivity resolved, sufficient binocular visual field, and no complications. Finding your vision good in the sitting room, in full light, has little to do with overtaking at night in the rain.

The most concrete issue is that of halos. After multifocal lens implantation, some patients perceive rings of light around light sources, troublesome mainly at night: in a small comparative series, 40% of bifocal implant wearers reported this, particularly while driving. A series of forty patients compared a trifocal lens with an extended depth-of-focus lens: halos and glare were perceived less with the extended depth-of-focus lens, but patient-reported night-driving scores were better in the trifocal group. These are small samples: they describe a trend, they do not quantify a risk. At meta-analysis scale — twenty-two studies and 2,200 eyes — halos and glare do not differ significantly between these two families.

After laser refractive surgery, the logic is the same. Dysphotopsias — halos, glare, degraded night vision — can appear, and one published case shows that a poorly centred presbyopia treatment can cause them persistently, to the point of justifying corrective surgery that made them disappear. This is an isolated case, and it says nothing about how common the phenomenon is. What it does say is something useful: persistent night-time discomfort after LASIK should be reported, it can be examined, and it sometimes has an identifiable mechanical explanation.

ONE EYE ONLY

What if I can only see out of one eye?

Here I need to say what I do not know. None of the systematic reviews gathered for this article gives its own estimate of accident risk for drivers who see out of only one eye; even the most comprehensive of them, which examined 48 studies, cannot reach a conclusion for most visual situations.

What can be described are the two losses. The first is depth perception, which relies on comparing the two images. The second is an amputation of the visual field on the side of the eye that no longer sees, with a sector that is only covered by head movements from then on. The first may matter less than one would imagine: in the seven-parameter analysis cited above, it was acuity, then field, that best explained driving cessation, not stereoacuity. That analysis was conducted in patients with glaucoma, who are not in the situation of having only one eye: it points to a direction, it does not measure the risk for a driver who sees out of only one eye.

Compensation, for its part, is documented indirectly. In drivers with glaucoma assessed on a closed circuit with eye-movement recording, those who made the widest saccades achieved the best driving scores — a link absent in controls. Actively scanning with the eyes is therefore not just a consolation: it is a serious lead, which the authors of this work — thirteen patients and ten controls — propose evaluating as a possible form of rehabilitation. This does not remove the need for a dedicated medical opinion, because vision in one eye only is treated specifically under French driving-licence regulations. And whatever the context, three situations mean you should not get behind the wheel and should see a doctor that same day: a sudden drop in vision, the sudden appearance of a blind area in the field of vision, double vision. If any of these signs comes on suddenly together with another neurological symptom — weakness on one side, difficulty speaking — in France, call 15 or 112; elsewhere, dial your own country’s emergency number.

INDEPENDENCE

Giving up driving: what it really costs

This chapter comes last, though it should often come first. A Cochrane review on visual screening of older drivers makes the point bluntly: stopping driving comes with negative emotional consequences, depression and loss of independence. A neurology review adds that, in peripheral visual field impairment, difficulty driving leads to stopping, stopping to loss of autonomy, and loss of autonomy to depression.

The figures rise with severity, without tracking it neatly. In a Japanese cohort of open-angle glaucoma followed for three years, driving cessation affected 1.3% of controls, 5.3% of mild glaucoma, 22.7% of moderate glaucoma and 18.2% of severe glaucoma — the last two groups numbering only 22 and 11 people. In a Canadian series, 19% of patients had stopped driving, with a marked gap by severity — 33% against 8%. At meta-analysis scale, driving cessation is associated with glaucoma and, even more strongly, with age-related macular degeneration.

One nuance remains that changes the tone of the conversation: many drivers adapt on their own, and well. A US naturalistic-driving study of 473 left turns shows this clearly: drivers with a visual deficit showed fewer problematic behaviours than the others, which the authors attribute to this acquired caution. The purpose of a consultation is therefore not to take away the car keys: it is to support an adaptation that, more often than not, has already begun.

REGULATIONS

What the law says, and why you won’t find a figure here

France has legal visual requirements for obtaining and keeping a driving licence, covering visual acuity and visual field among other things. These are not the same for a standard licence as for a heavy-vehicle or professional licence, the latter being considerably stricter, and they provide for special cases, including that of vision in one eye only. We deliberately do not reproduce them here: a threshold taken out of the conditions in which it applies helps no one, and it is the approved doctor who weighs it against your own situation. The reference text is the French Order of 28 March 2022, which sets out the list of medical conditions incompatible with driving, or compatible subject to conditions; it is public and can be consulted on Légifrance and Service-Public.fr. The threshold that applies to the French Category B licence is also given on our page about visual acuity.

The second point is just as important: it is not your ophthalmologist who decides. Fitness to drive is for a doctor approved by the prefect, or a medical panel, to decide. The ophthalmologist’s role is to supply the measurements — acuity, visual field, sometimes more — and to explain what they mean. A retired neurosurgeon published his own case: at 81, he had a visual field quadrant amputation that did not interfere with any daily activity, and that he only recognised thanks to his own profession. Self-assessment, on its own, is not enough.

Finally, these thresholds themselves are debated. A comparison of European rules shows that they amount to a lowest common denominator between member states, and that the relevant limit for visual field remains undetermined. A recent study applied Swiss, Swedish, Norwegian and British criteria — four European countries that invoke the same standard, though not all are members of the Union — to the same 243 patients: fitness rates ranged from 65% to 86% depending on the country. And the Cochrane review found no study demonstrating that visual screening of older drivers reduces accidents.

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This article is intended for information purposes and does not replace a medical consultation. Indications, expected benefits and risks depend on each individual situation. For any question concerning your vision, consult an ophthalmologist.