Most Divers Who Cannot See Solve It the One Way an Eye Doctor Would Not

A dive mask has to seal against your face, which is precisely where the arms of a pair of glasses go. That geometric fact has pushed several generations of short-sighted divers toward contact lenses, usually without anybody raising an objection.

There is an objection. It is not the one most divers expect, it is not about the lens popping out, and it is worth knowing before your next trip.

Is it safe to dive in contact lenses?

It depends entirely on which kind, and the difference is physical.

Soft lenses rarely cause trouble underwater. They are permeable enough to let gas pass through, so nitrogen absorbed under pressure escapes without leaving anything trapped against the cornea. Divers Alert Network treats them as broadly workable.

Rigid gas permeable and hard lenses are a different matter, and DAN advises against diving in them. Under increasing ambient pressure they can suction painfully onto the eye. Worse, gas can become trapped between the lens and the cornea, producing bubbles that blur vision at exactly the depth where you would like to read a gauge. Neither problem is an emergency on its own. Both are unpleasant distractions at a moment when your attention has other work to do.

So the standard advice, if you are diving in soft lenses, is to close your eyes if your mask floods or you have to remove it, because an open eye in moving water is how a lens leaves. And carry glasses on the boat, because a diver who has lost a lens and cannot see the dive plan has a problem the sea does not care about.

The risk almost nobody mentions

Here is the part that changes the calculation, and it has nothing to do with the lens falling out.

Acanthamoeba is an amoeba that lives in water. Fresh water especially, but water generally. It can infect the cornea, and Acanthamoeba keratitis is a genuinely serious condition: painful, difficult to treat, and capable of costing sight.

It is rare. But research cited by DAN found that 85 per cent of cases occurred in contact lens wearers who had worn their lenses while swimming or diving. As the ophthalmologist Robert Sanders puts it in DAN's own guidance, any water is prone to bacteria.

The mechanism is unremarkable, which is what makes it easy to ignore. A contact lens sits directly against the cornea and holds whatever gets underneath it in prolonged contact with the eye. A splash of seawater in your face is trivial. The same water pinned against your cornea for the rest of a dive is not the same exposure at all.

The practical rule that follows: if water enters your mask while you are wearing lenses, take them out afterwards. Not that evening. Afterwards. And do not reuse them. Daily disposables are the sensible format for divers for exactly this reason, since throwing a lens away costs less than the alternative.

What about a prescription mask?

This is the option most divers assume is exotic and expensive, and for a lot of prescriptions it is neither.