If you had to give up one of your five senses, which one would it be? For most of us, eyesight would be at the bottom of the list. We rely on our sense of sight to walk, drive, read, write, recognize loved ones, and identify threats. If you suddenly lost your vision during an emergency, your odds of survival would undoubtedly be low.

Learning to navigate blindly would be a real challenge during a survival situation.

Those of us who have poor eyesight know all too well how difficult it can be to go about daily life without corrective lenses — either glasses or contacts. In an emergency, these items can be lost, damaged, or become inaccessible. Disposable contact lenses will eventually be used up and thrown away. If you're prepared, you'll have backups of these items or will save up for laser surgery, but it's still wise to have a fall-back plan in case things really go south and you can't see clearly.

Unless you're a trained optician with a full set of working equipment, it's not exactly feasible to make a new set of lenses that match your eyes. However, there's another much simpler option: pinhole glasses. Instead of concave or convex lenses, these glasses use tiny holes to allow through very narrow beams of light, much like the pinhole camera you probably made in elementary school science class. This effectively increases depth of field and gives you sharper vision.

Off-the-shelf pinhole glasses contain evenly-spaced pinholes in opaque plastic. Photo: Wikipedia

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If you're curious about the value of this pinhole effect, you can test it easily at home. Just grab a sheet of dark paper and poke a pinhole through it. Then take off your corrective lenses and hold the paper with the pinhole just in front of your eye. Your vision will be far from perfect, but you should still see a dramatic improvement. More pinholes will allow in more light and provide peripheral vision.

Another method of testing this pinhole effect is to form a loose fist, and hold it up to your eye like you're holding an invisible telescope. Tighten your grip until only a pinhole of light is visible, and watch as once-blurry objects come into focus.

Like eyeglasses or contacts, pinhole glasses are only a temporary fix for poor vision. However, these are much easier to improvise in an emergency — just black out some cheap sunglass lenses and carefully punch some holes. You can even make them out of aluminum foil, as long as you don't mind looking like a low-budget version of Cyclops from X-Men. Either way, improvised pinhole glasses can give you a fall-back option in case your glasses or contacts are unavailable in an emergency.

Written by Patrick McCarthy