Dry eye in an air-conditioned city

Dry eye is among the most frequent reasons people come to an optometrist, and among the most frequently self-treated with whatever is available at the pharmacy. It is worth understanding, because the treatment that helps depends on which kind you have — and because the commonest kind is not actually a shortage of tears.

The counterintuitive symptom

Watery eyes are a classic sign of dry eye. When the surface dries out, it is irritated, and irritation triggers a flood of reflex tears — which are watery, poorly composed, and spill over rather than coating the eye properly. So the eye is both streaming and dry at once.

The rest of the picture: grittiness, as though there is sand in the eye; burning or stinging; tired eyes by the afternoon; intermittent blurring that clears when you blink; discomfort with contact lenses; and, often, symptoms that are worst in the morning or after a long stretch of screen work.

Two mechanisms

The tear film has an aqueous layer, which is water and the substances dissolved in it, and a thin oily layer on top that stops the water evaporating.

Aqueous deficiency is not producing enough of the watery layer. It is associated with age, with some medications — antihistamines, certain blood pressure drugs, antidepressants, hormonal contraceptives — and with autoimmune conditions.

Evaporative dry eye is producing enough tears but losing them too fast, because the oil layer is inadequate. This is by far the commoner form, and it usually traces to the meibomian glands in the eyelid margins becoming blocked or their secretion becoming thickened.

The distinction matters. Artificial tears added on top of a tear film that is evaporating too quickly give twenty minutes of relief and no more, which is why people work through bottle after bottle without improvement.

Why Lagos is hard on the tear film

Air conditioning is dehumidifying by design, and most offices run it all day. Ceiling and standing fans move air across the face continuously. Harmattan brings dry, dusty air for weeks. Traffic pollution irritates the ocular surface. And a working day at a screen halves the blink rate — blinking is what spreads the oil layer, so less blinking means faster evaporation.

That combination is close to a recipe for evaporative dry eye, and it explains why so much of it turns up in practice here.

What helps

Warm compresses and lid hygiene, for the evaporative form. Sustained warmth over closed lids for several minutes softens the thickened oil so the glands can clear, followed by gentle massage along the lid margin and cleaning with a lid wipe or dilute baby shampoo on a clean cloth. Done consistently over weeks, this is more effective than any drop. Done once, it does nothing — which is why most people conclude it does not work.

Artificial tears, chosen deliberately. Preservative-free if you use them more than four times a day, because the preservatives themselves irritate the surface with frequent use. Thicker gel formulations last longer and blur more, which makes them suitable at night.

Environmental changes. Direct the fan away from your face. Position the screen slightly below eye level so the lids cover more of the eye. Take breaks. Blink deliberately and completely — a genuinely effective intervention that costs nothing.

Reviewing medications with whoever prescribed them, if a drug you take is a known contributor.

Treating the underlying lid disease. Blepharitis and rosacea are common and treatable, and dry eye that does not improve usually has one of them behind it.

What to avoid

Whitening drops that "get the red out" work by constricting blood vessels. They treat the appearance and not the cause, and stopping them after regular use produces rebound redness that is worse than the original. They are not a dry eye treatment.

Steroid drops have a legitimate short-term role in inflammatory dry eye, prescribed and monitored. Used casually and long-term they raise intraocular pressure and accelerate cataract. They are not something to borrow from a relative.

When to have it looked at

If symptoms persist for more than a few weeks despite the measures above, have the ocular surface examined. Dry eye is diagnosable in detail — tear film stability, tear volume, gland structure, surface staining — and the diagnosis determines which of the treatments above is worth your effort. Persistent dry eye can also damage the cornea, which is a better reason to have it assessed than the discomfort alone.