Driving in Lagos, and the vision it requires

Driving places demands on vision that ordinary life does not. Lagos adds several of its own: unlit stretches, oncoming headlights at full beam, potholes that appear late, pedestrians and okada riders emerging from the periphery, and a great deal of night driving in traffic.

Several of the visual functions that matter here are not measured by reading a letter chart, which is why people can pass a sight test and still find driving difficult.

What driving actually uses

Distance acuity — reading signs, seeing a stationary obstruction in time. This is the one the chart measures.

Visual field. Peripheral vision is what detects the pedestrian stepping out and the vehicle changing lane. Advanced glaucoma, a stroke affecting the visual pathway, or a retinal condition can remove substantial peripheral field without affecting acuity at all. This is why glaucoma matters for driving long before it affects reading.

Contrast sensitivity. The ability to distinguish an object from a background of similar brightness — a dark figure at dusk, a grey road edge in rain. Early cataract degrades contrast sensitivity well before it affects chart acuity, which is why someone can read the chart perfectly and still find the road ahead indistinct.

Glare recovery. How long it takes to see again after oncoming headlights. Also degraded by cataract, and by an untreated or poorly made prescription.

Depth perception, which depends on both eyes working together. Judging following distance and closing speed.

What the common complaints mean

"Headlights dazzle me more than they used to." The commonest cause is early cataract scattering light inside the eye. Uncorrected astigmatism and scratched or uncoated spectacle lenses also contribute.

"I can see fine but I am not comfortable at night." Often a small uncorrected prescription that matters only in low light, when the pupil is large. Sometimes reduced contrast sensitivity.

"I keep being surprised by things at the side." This one deserves attention rather than reassurance. Peripheral field loss is silent, and glaucoma is the commonest cause.

"I have started needing to get very close to read signs." Usually a straightforward refractive change.

Practical measures

Have an examination, including the retina and the visual field where indicated. Keep the prescription current. Anti-reflection coating on your lenses genuinely helps at night — it reduces the reflections bouncing between lens surfaces that spread headlight glare.

Keep the windscreen clean inside as well as out; the interior film scatters light considerably. Dim the dashboard. Do not look directly at oncoming headlights — look towards the left edge of your lane and use peripheral vision to track the other vehicle.

Do not wear sunglasses or "night driving" tinted lenses after dark. Yellow-tinted night driving glasses are widely sold and do not improve night vision; they reduce the total light reaching the eye, which in darkness is the opposite of helpful.

Commercial drivers

Anyone driving for a living — commercial buses, taxis, ride-hailing, haulage — is carrying other people's safety and should be examined annually rather than when something becomes noticeable. Long hours, much of it at night, in a city where lighting is inconsistent, is the demanding end of the spectrum.

Employers arranging periodic vision screening for drivers are doing something straightforwardly worthwhile, and the chapter's members can arrange it.

Monocular drivers

People with sight in only one eye can and do drive safely, having adapted their depth judgement over time. Two things matter: protecting the remaining eye with impact-resistant lenses, and having it examined regularly, because there is no spare.

The honest bit

Vision declines gradually and the driver adapts gradually, which is why the person least well placed to judge whether their sight is still adequate for driving is the driver. If family members have started commenting, or if you have begun avoiding night driving without quite deciding to, have an examination. Most of what is found is correctable.