Sunglasses are eye care, not an accessory

Ultraviolet light damages the eye cumulatively. Not dramatically, not on any particular day, but steadily across decades — and Lagos, at six degrees north, has high UV year round, with no seasonal respite.

What the exposure does

Cataract. UV exposure is an established risk factor for cortical cataract in particular. Cataract remains the leading cause of blindness in Nigeria, and although it is surgically treatable, the surgery has to be available, affordable and reached in time.

Pterygium. The fleshy, wedge-shaped growth that creeps from the corner of the eye across the cornea. It is strongly associated with UV exposure, dust and wind, and it is common enough here that most people have seen one without knowing what it was. Small ones are cosmetic; larger ones distort the cornea, blur vision, and may need surgical removal — after which they often recur.

Photokeratitis. Effectively sunburn of the corneal surface, from an intense short exposure — welding without a shield, or strong reflected glare. Painful, and it arrives some hours after the exposure. It heals, but it is entirely preventable.

Macular degeneration. The evidence linking lifetime UV exposure to age-related macular degeneration is suggestive rather than settled, but it points the same direction.

Eyelid skin cancers. The eyelids are thin skin in a highly exposed position, and a meaningful share of skin cancers occur there.

The thing most people get wrong

Dark lenses that do not block UV are worse than wearing nothing.

Your pupil responds to visible brightness. Put a dark lens in front of it and the pupil opens. If that lens is not blocking ultraviolet, you have widened the aperture and let more UV into the eye than you would have with bare eyes squinting in the sun.

Tint and UV protection are separate properties. A completely clear lens can block all of it; an opaque black one can block none.

What to look for

• UV400, or "100% UV protection". This is the only specification that matters. If a pair carries no marking and the seller cannot tell you, assume it has none.
• Coverage. Light reaches the eye from the sides and from above. A wraparound shape or a larger lens does substantially more than a small one, and a wide-brimmed hat adds as much again.
• Polarisation for glare — reflections off water, wet roads, car bonnets. It is a comfort feature, not a protective one; polarised lenses without UV protection are still a bad pair.
• Tint depth to suit the use. Mid-to-dark grey or brown for general outdoor use. Grey preserves colour relationships most faithfully, which matters for driving.

Price is a poor guide in both directions. Inexpensive sunglasses from a reputable source are frequently properly UV-rated; expensive fashion frames from an unknown stall may not be. If in doubt, an optometrist can measure a pair's UV transmission in seconds.

Children

Children's lenses are clearer and their pupils larger, so more UV reaches the retina than in an adult eye — and their lifetime exposure is only beginning. A significant fraction of total UV exposure is accumulated before the age of eighteen. Sunglasses and hats for children are not fussiness.

This sits alongside the point that time outdoors protects children from becoming short-sighted. The two are not in conflict: the answer is to go outside, with protection, not to stay in.

At work

Welding, grinding and cutting produce intense UV and require proper shielding, not sunglasses. Drivers, traders, artisans and anyone else working outdoors through the day carry a much larger cumulative dose than most people and benefit most from a decent pair.

If you already wear a prescription, sunglasses can be made to it, or you can have a photochromic lens that darkens outdoors. Ask your optometrist which is more practical for how you actually spend your day.